Ref80 - A competition to ADR1001? - Page 1
Forum section: electronics / general

author: branadic
author_rank: Super Contributor
timestamp: September 23, 2024, 05:23:24 pm
content: "REF80 is a buried zener, internal heater compensated voltage reference. The device is designed with an extremely low temperature drift and long-term drift. REF80 is also a low noise device."https://device.report/m/158081276c8014e611d4be1e2e7e80c15bf10773f92c56a97763852ea16d52fd.pdfHas TI really worked on a competition to ADR1001? HP3458A reading in figure 2-3 indicates a zener voltage of 7.577 V.-branadic-

author: mendip_discovery
author_rank: Super Contributor
timestamp: September 23, 2024, 05:43:48 pm
content: Quote from: branadic on September 23, 2024, 05:23:24 pmoooh, that sounds interesting. I guess AD have kinda dropped the ball a bit with the ADR1001 as they have only managed to produce a new ref much like the old one but not as good (YMMV).Looks like this is very early info so will wait to see what happens.EDIT:Looking at the site there is a REF70,https://www.ti.com/lit/ds/symlink/ref70.pdfLong-term stability: 1k hrs: 35 ppmCoefficients: 2ppm per deg Ceven newer is the REF54,https://www.ti.com/product/REF54

author: iMo
author_rank: Super Contributor
timestamp: September 23, 2024, 06:21:20 pm
content: Let us wait on REF90.. With the opamps and 5V/10V dividers in the oven.What is interesting to see is the pcb layout of the eval kit - how are the slots around the package arranged..

author: jbb
author_rank: Super Contributor
timestamp: September 24, 2024, 12:15:11 am
content: Having another vendor for high precision references would be welcome.I wouldn’t expect a drop-in replacement, but having a competitor to Analog Devices in the game is a good thing.

author: laichh
author_rank: Regular Contributor
timestamp: September 24, 2024, 02:49:59 am
content: Identical file was found on ti.com domain:https://www.ti.com/lit/ug/snau304/snau304.pdfFrom the schematic in Figure 4-1, this REF80 doesn't have the derived output (+5 V, +10 V...) like the ADR1001, only the zener output at ~7.6 V is available.Traditionally, TI's alternative is often (if not always) cheaper than ADI. ADR1001 1ku listed price on ADI is $66.34, I would expect this REF80 to be range between $35 ~ $50 each.

author: ArdWar
author_rank: Frequent Contributor
timestamp: September 24, 2024, 05:22:09 am
content: Interesting, the pinout is MostlyCompatible™ with ADR1001.Is this TI's first foray into buried zener technology? I don't think their other references are buried zener (LMx99 don't count)

author: Andreas
author_rank: Super Contributor
timestamp: September 24, 2024, 05:35:13 am
content: What about REF102 (Burr Brown Division)?

author: 3roomlab
author_rank: Frequent Contributor
timestamp: September 24, 2024, 06:31:59 am
content: nicethe slotting they use is so smalllike size of the 2.54mm pin (~ 0.4mm ?)* mr imo is right, more like 1mm slot

author: Kleinstein
author_rank: Super Contributor
timestamp: September 24, 2024, 07:23:13 am
content: Quote from: Andreas on September 24, 2024, 05:35:13 amThe REF102 is a nice 10 V reference, but the metal case seems to be no longer available.How good the Ref80 will actually be is still unclear. There is not even a preview data-sheet. It may as well be more competing with the LCC version or the ADR1399.The slightly higher voltage is a bit odd and rather high for zener plus PN junction.

author: iMo
author_rank: Super Contributor
timestamp: September 24, 2024, 12:36:07 pm
content: Quote from: 3roomlab on September 24, 2024, 06:31:59 amThe pitch of the package pins is 1.27mm. Thus the slots are aprox 1mm wide, imho.The slots' layout seems to help with the mechanical stress as well.So let us copy that layout for the ADR1001 as well..

author: Kleinstein
author_rank: Super Contributor
timestamp: September 24, 2024, 01:20:10 pm
content: The slots are for mechnical stress and to keep the thermal loss low, though much of the heat loss can still be via the copper traces. It thus makes sense to have separate drive and sense pins for the output and also separate grounds for the reference and the heater.

author: iMo
author_rank: Super Contributor
timestamp: September 24, 2024, 01:27:09 pm
content: Quote from: Kleinstein on September 24, 2024, 01:20:10 pmI've been planning the pcb for 2y alreadyand perhaps the other owners do too, let us continue in the ADR1001 thread and let us design the pcb finally..

author: laichh
author_rank: Regular Contributor
timestamp: October 01, 2024, 05:28:06 am
content: A dedicated page for REF8EVM is now available on ti.com.https://www.ti.com/tool/REF8EVMStill no DS was found.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 02, 2024, 01:41:17 am
content: Page is now up, with datahttps://www.ti.com/product/REF801-99 $84.841100-249 $82.289250-999 $68.5101,000+ $63.790

author: laichh
author_rank: Regular Contributor
timestamp: October 02, 2024, 02:56:31 am
content: Well, in summary, the REF80 is about half the TC & double the noise vs. the ADR1001. Can't tell about the long-term stability as the chart provided is only up to 1000 hours.Parameter| LT LTZ1000ACH| ADI ADR1001| TI REF80| UnitReleased| 1987| Jan-2024| Oct-2024 (Preview)| YearZener Voltage| 7.2| 6.6| 7.6| VNoise (0.1~10 Hz)| 1.2 @ 5 mA| 0.6 @ 4 mA| 1.2 @ 15 mA| µVpp (Typ)Temp Coef| 0.05| 0.2| 0.05| ppm/°C (Typ)Price (1ku)| $59.92| $66.34| $63.79| USD

author: floobydust
author_rank: Super Contributor
timestamp: October 02, 2024, 04:09:35 am
content: I have an issue with piling on the output capacitance in order to achieve that datasheet glory low noise number.The EVM ref output film caps- one SMT, the other Wima the only through-hole part really for total 20uF+0.22Ω seems heavy handed. Sigh.That doc is looking pretty sloppy for August, TI lazy copy'n'paste errors galore:It's not a REV54EVM, isn't is a REF8EVM?"4.2 PCB Layouts""REF54EVM is a two layer board."Uh no, figures 4-4, 4-5 show layers 3 and 4. Isn't it a REF8EVM? Who gets paid to do such low quality editing work."4.1 Schematics""The schematic for the REF8EVM is illustrated in Figure 3-3"Uh no, figure 4-1 shows the schematic.Heater voltage can be 10-42V for 75-18mA hot TSET=115°C for around 0.75W

author: Andreas
author_rank: Super Contributor
timestamp: October 02, 2024, 04:26:52 am
content: Quote from: laichh on October 02, 2024, 02:56:31 amAlso interesting the zener current vs. noise.with best regardsAndreas

author: ArdWar
author_rank: Frequent Contributor
timestamp: October 02, 2024, 04:39:32 am
content: What kind of temperature control are they using?Fig 9-2 hints something two stage, not fully linear, and VREFZ is gated before OPSTBL is asserted?Quote from: Page 9They put digital mgmt inside?Now instead of worrying about RTSETdrift we worry about how good the sample and hold circuitry holds its value?

author: Kleinstein
author_rank: Super Contributor
timestamp: October 02, 2024, 11:41:21 am
content: For the temperature there seem to be only 4 discrete temperature to chose: 115 C, 105 C, 95 C and 85 C. So all relatively high.Looks like a digital solution for the set temperature. The actual regulation is likely still analog even though a long time constant is also attractive to realize digital.The supply current for the zener part is also quite high (15 mA) and thus quite some self heating and much below 85 C may not be that practical anyway, if the thermal resistance is high.Overall it's a power hungy solution.The DS numbers look good for the long term drift, but not so much with the noise. The shown noise is relatively high at the shown higher frequencies and the true LF noise below the 1/10 Hz may not be that bad. The actual drift will also depend on the PCB, though no critical external parts.

author: tszaboo
author_rank: Super Contributor
timestamp: October 02, 2024, 12:07:40 pm
content: Quote from: ArdWar on October 02, 2024, 04:39:32 amIt's likely not a sample and hold circuit. TI uses this in many ICs now: They sample a voltage divider (external resistor) on startup and then set up a DAC based on this sample. That's why you have ICs (for example voltage regulators) where there are specific values for external resistors which set up specific values of voltages. And it allows very low power consumption, since you can shutdown the sampling of the resistor, which is clearly not a requirement here.The IC is interesting. The eval board is a bit MEH. They put a lot of effort to isolate the heat generated by the part from the rest of the PCB, insead of concentrating on air currents and thermouple effects. It also seems to use regular banana plugs, not even gold plated ones. Also, LM317I don't think the engineer putting the ref board together has put too much tough into it.

author: macaba
author_rank: Regular Contributor
timestamp: October 02, 2024, 02:28:43 pm
content: To answer the thread title, "Ref80 - A competition to ADR1001?"Not really.Three things that stand out to me: zener noise to supply current figure-of-merit is bad. >300mA inrush on power up is bad & no mention of a 10 ohm, or something, resistor to limit it. The price is a little high when holistically considered against competitors. There will be other (good & bad) things also but those jumped out at me today.On the positive side though - it's evidence TI have a team who can design this level of reference and that can only be a good thing going forward. For those reading this - thanks, I hope you get approval for more products like this.

author: dlebed
author_rank: Regular Contributor
timestamp: October 20, 2024, 03:18:38 am
content: Since ADI chose not to sell (!) me the ADR1001 for whatever reason, I decided to entertain myself with REF80, which I managed to get my hands on.I only was able to build a barebone prototype board, but should be enough for basic measurements (assuming you have a low noise power supply).Here are my results so far, after spending couple hours testing it.- it's currently missing the thermal insulation (it's on its way)- output filter cap is C0G + 2 x X7R for now, will need to replace X7R with film capI decided to run the reference at max. temperature setpoint (115C) for a month to speed up aging, then I'll change the setpoint to 85C.My first REF80 at 115C settled at 7.568V.External case temperature is just a little shy of 90C.As you can see from thermal images below, board cutouts are quite effective and help with thermal isolation of REF80.I went against datasheet recommendations and put a symmetrical round copper pour under the REF80 itself to spread the heat evenly (it anyway will be thermally insulated).TopBottomI'm running both heater and bias at 15V, the total current with well insulated REF80 is 32mA @ 15V (0.5W) (this is again 115C heater setpoint with ~25C ambient).Measuring it with a few 3458a's and DMM7510 there is clearly an expected downward aging trend seen even over couple hours.I have quite a few ideas in mind of what to do with it, so I will post updates here. I'll try to measure output impedance and post results soon.Unfortunately, I don't have a good noise measurement setup, so I could not make any meaningful noise measurements yet.If anyone has suggestions for specific tests to try with it, please let me know, and I'll see if I can give them a shot.Here are the design fileshttps://github.com/dlebed/ref80-basicP.S.You can order the board on oshpark if you wanthttps://oshpark.com/shared_projects/kTTHxNFD

author: aronake
author_rank: Frequent Contributor
timestamp: October 20, 2024, 03:43:36 am
content: Quote from: dlebed on October 20, 2024, 03:18:38 amIf ADI do not want to sell a ADR1001, maybe you can try Mouser:https://www.mouser.com/ProductDetail/Analog-Devices/ADR1001AEZ?qs=ZcfC38r4PosJwibAPZPq6Q%3D%3D17 in stock now.Seems you live in USA, and if you do not click the boxes that you intend to use it for military purposes or resell it to some evil country, there ought to be no problem buying. I got 2 ADR1001 and one evaluation borad sent to Hong Kong which should be pretty high up on the evil list.

author: dlebed
author_rank: Regular Contributor
timestamp: October 20, 2024, 04:22:03 am
content: aronake, you supposedly could buy ADR1001 much cheaper from ADI directly, but somehow they've cancelled my order.Right about that time I stumbled upon REF80, so I just decided to try this new beast instead.Maybe later I'll buy ADR1001 from Mouser, but I need to finish my LTZ1000 and REF80 designs first

author: iMo
author_rank: Super Contributor
timestamp: October 20, 2024, 08:14:53 am
content: Quote from: dlebed on October 20, 2024, 03:18:38 amThe cutouts - I would prefer the shape as in the kit DS - that helps with the mechanical stress a bit, not sure your design is more effective in this regard..Aging at 115C might be significant, imho, my ADR1001 spent some 2 days at around the same temperature (by my mistake, call it fast burn-in) and it moved down with the voltage as well. Also I would not run it at 115C for a longer period, however.PS: internal 115C with the case 90C sounds a bit odd, the temperature difference should be much higher, imo.

author: Andreas
author_rank: Super Contributor
timestamp: October 20, 2024, 10:00:22 am
content: Quote from: dlebed on October 20, 2024, 03:18:38 amHello,for me the most interesting test would be how the environment humidity (swelling the of the PCB by humidity) influences the SMD package.2 steps:- power the REF80 24/7 until the readings stabilize.- power off for about 2 weeks or longer (in my location this would be best in summer when the air humidity is high).Check wether there is a jump in readings after 2 weeks pausing and how long does it need to restore to the old value.with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: October 20, 2024, 11:16:27 am
content: Or put it into your fridge for some time, the humidity there is usually high..

author: Kleinstein
author_rank: Super Contributor
timestamp: October 20, 2024, 11:38:39 am
content: The possibly humidity effect is indeed one of the points to check. A low temperature would only extend the time needed for the humidity to enter the plastic parts. Some 2 weeks at normal room conditions, maybe a more humid (e.g. >= 50RH) box if needed would be better.The ceramic case itself should be pretty resistant to humidity, but the PCB can swell a little and the mechanical stress can than have an effect.The copper fill on the backside may slow down the entry of humity a little.Possible hysteresis from some time at room temperature can be from humidity, but also from thermal stress and similar. If too large one may have to run the reference hot 24/7 to really get a stable value. Here it does not really matter if the effect is more humidity or thermal stress relaxation.If the reference is used powered on 24/7, the humidity effect may not be that bad, has the hot part naturally has pretty low RH.With the rather high power consumption it may not be that attractive to have it powered all the time.A number that could be interesting could also be the current consumption with the different temperature settings. So to judge on the overall heat loss / thermal resistance.

author: dlebed
author_rank: Regular Contributor
timestamp: October 20, 2024, 06:20:44 pm
content: As for the cutouts, they also intended to help with mechanical stress, but there are 2 not so obvious things about my design:- I left a small board bridge on the right that could easily be cut, in that case none of main board flex will be transferred to the reference- I plan to put a square "cage" around the reference (parts are on the way), it should stiffen the reference PCB area and help with with mechanical stress reduction if you don't cut the bridgeIf you cut the link on the right (there are no traces going through it), reference will be pretty much mechanically isolated.The only problem might be is vibration and resonance...I cut that bridge on one of the boards and the reference island looks quite stiff and solid, so I think that bridge could be removed in future board designs from the beginning.Mechanical resonance issues (if there are any) during transportation could probably be solved by adding some foam padding at the bottom.Now, regarding the case temperature and thermal resistance.As you clearly see from thermal images, huge difference in thermal emissivity between different parts of the package makes contactless temperature measurement challenging.I made a couple of measurements with a thermocouple today:- GND pin temperature is 92C- top of the lid is ~83C (it's hard to get good thermal contact with it)Thermocouple measurements are very close to thermal imaging camera measurements.I use emissivity coefficient of 0.95 for all of my measurement, but looks like if you only look at ceramic temperature (as all metals has very low emissivity anyway) and assume ceramic emissivity to be 0.9 instead of 0.95, then thermocouple measurements match exactly to the ones I got with thermal camera.At the time of measurement there was no thermal insulation, the reference was consuming 38mA@15V = 0.57W.So these temperature differences assuming 115C die temperature gives roughly next thermal resistance numbers:Rjunction-lead = (115 - 92) / 0.57 = 40 C/WRjunction-case = (115 - 83) / 0.57 = 56 C/WThat's not that great (compared to LTZ1000A), but as you can see from the thermal images, with good enough cutout design all that high temperatures are pretty much isolated to the reference itself.As you can see from image below, temperature at the board bridge connecting board to the reference island is around 40C. Board itself is at about 31C and ambient is around 26C.

author: dlebed
author_rank: Regular Contributor
timestamp: October 20, 2024, 06:37:13 pm
content: Thanks for all the ideas on how to test its humidity resistanceI'll do it once readings stabilize. I just want to go though accelerated aging first, then lower the oven temperature and do all of the stability checks.I also will check for power consumption at different heater setpoints for sure, I was planning to run it at 85C once it settled anyway.So far, it lost 8ppm over first 16 hours at 115C.BTW, my power consumption numbers are quite different from TI's datasheet numbers.They claim it will burn 0.75W just for the heater + another 0.225 W (@15W) for bias for 115°C setpoint, totalling in 1W @15V/25°C.In my case, it only burns 0.48W @15V if thermally insulated (plastic boxes from top and bottom) and 0.55W if it just sits in open air with no cover.Since all of that 15mA bias current contributes to heating, lowering bias supply voltage will likely have no effect on the power consumption.So, with that 0.55W power consumption in open air at 26°C ambient,θJAbecomes (115-26) / 0.55 =162 °C/W, which issomehow even better than what ADR1001's datasheet eval board numberof 140 C/W claimed to be.P.S. I'll also try to measure its unheated tempco and heated tempco later.

author: floobydust
author_rank: Super Contributor
timestamp: October 20, 2024, 06:46:08 pm
content: I guess the challenge will be insulating the REF80 and minimizing conduction heat losses through the PCB traces.I think where this goes is the LTZ1000Adie-attach technology that insulates... "hey we at TI should develop that" lol."hey we at ADI should not have fired the guys who know how to make that goop up" lol.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 20, 2024, 06:49:59 pm
content: The mechanical stress has multiple components. The stress from the outside PCB and mounting holes is one part. Here cutting the thin link would help. However there is also the difference in the thermal expansion, e.g. between the ceramic case and PCB directly under the chip. Another part is humidity inside the PCB material that makes the material swell a little and this way create some stress. So it is not only the outer stress, but already the PCB just below the chip that can cause stress. Ideally there would also be some cuts / holes to reduce that stress at least.The ref80 really wants the thermal insulation / temperature gradient at the PCB level, not inside the ceramic.The relatively high temperatue compared to the typical LTZ1000 / ADR1000 circuits adds to the power needed. For the final use case I would definitely mainly consider the lowest temperature setting unless there is a special problem with this. One can't get very low as the reference part already uses more power. For high thermal resistance (good PCB ) and a bit higher environmental temperature one may have to lower the supply voltage - still not that much reduction possible from 15 V.The required power will depend on the PCB and added isolation - the DS numbers may be for a simpler PCB with less cuts / more copper.

author: iMo
author_rank: Super Contributor
timestamp: October 20, 2024, 06:58:03 pm
content: The ADR1001 has got the same package, but its Rth_JA=120C/W.It seems the REF80 is missing the glass balls there, imho..At 120C mine was perhaps 40-45C at the lid (finger method) as I can remember.PS: when looking back in my thread - it took 50mA (@15V) current with my wrongly set 120C..

author: dlebed
author_rank: Regular Contributor
timestamp: October 20, 2024, 07:04:21 pm
content: θJA is a function of board design as well and in my case it is about 160 °C/W, which is even better than the ADI's ADR1001 numbers...My board is quite small though.I really need to make the same board for ADR1001 (need to source ADR1001 first though) to do apples to apple comparison for them...I know that the PCB itself could create mechanical stress for the ceramic-packaged reference and I was thinking on making the reference island from flex PCB (polyimide)...The problem is to make it mechanically sound and to be able to make a good connection to main PCB without getting any thermal EMF issues though.

author: Andreas
author_rank: Super Contributor
timestamp: October 20, 2024, 07:15:41 pm
content: Hello,another parameter would be board thickness.I usually use 1.0 mm instead of the normal 1.6 mm for my cirquits.with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: October 20, 2024, 07:18:31 pm
content: ..or for example a complete pcb with a reduced thickness of say 0.4mm and the cutouts like in the ref80 dev kit..PS: the thinnest is 0.4mm in jlcpcb and 0.2mm in pcbway for example..PPS: and Noopy needs to get one chip as well, of course..

author: floobydust
author_rank: Super Contributor
timestamp: October 20, 2024, 07:36:29 pm
content: Leadless packages have no leads to take up thermal expansion stress.https://www.sciencedirect.com/science/article/abs/pii/S0026271422000567discusses the CTE difference between LCCC ceramic and FR-4:Ceramic package substrate CTE: 5 to 7x10−6/°CFR-4 PCB CTE: 14-17x10−6/°C (looks like almost triple)Mentions using an 0.3mm FR4 PCB spacer to lessen the stress and solder joint cracking- which is a known problem with the ceramic SMT packages. Solder height is also a big deal.https://www.analog.com/media/en/technical-documentation/application-notes/4326543067473486309AN652_0.pdfa little more in mems applications that also use the package.

author: dlebed
author_rank: Regular Contributor
timestamp: October 21, 2024, 03:05:43 am
content: I wanted to stick with what OSH Park could offer as their materials are top notch (much better than JLCPCB).Since FR4 is not really conducting heat very much I went with 1.6mm 1oz stackup.I could give a try with theirs 0.8mm 2oz and maybe also make some hybrid flex design to see if flex PCB could be the ultimate savior for LCCC ceramic packaged references.

author: dlebed
author_rank: Regular Contributor
timestamp: October 21, 2024, 03:38:26 am
content: Actually, one mystery that will needs to be solved is if I figured out the sense/force pins correctly (they're not particularly well documented).Maybe if I decap one, it will be easier to tell...Any idea what kind of solder could be used to attach the lid? Is it better to heat it up to ~250-270C or try to put a blade in between the lid and package?

author: Andreas
author_rank: Super Contributor
timestamp: October 21, 2024, 04:49:57 am
content: perhaps not in the datasheet.but in the reference board description.with best regardsAndreas

author: dlebed
author_rank: Regular Contributor
timestamp: October 21, 2024, 05:24:22 am
content: Andreas, yes, I figured that out and implemented that in my design, but on the GND pins it's less clear as there are 3 GND pins on the reference side. They likely have different connections/functions, but it's not documented in datasheet/reference board.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 21, 2024, 08:07:07 am
content: For the ground pins there are some informations in the data-sheet. Pin 13 is the ground for the control circuit power, so the amplifier and maybe the heater regulator. Pins 14 and 15 are the ground for the zener reference itself. These 2 may very well be equivalent, just 2 separate links / bond wires. The likely purpose is to use one to sink the current (so connected to power ground) and the other to sense the output voltage (e.g. act as the precision ground for the rest of the circuit).Alternatively one pin connects to the precision ground and the other gets a constant current of some -15 mA, so that ideally there is no current in the precision ground link.For the PCB shown one may consider to interrupt the link between the pins 14 and 15, so that the 2 seprate links to the outside are used separately: pin 14 as sense and pin 15 for power ground.

author: dlebed
author_rank: Regular Contributor
timestamp: October 21, 2024, 03:49:27 pm
content: Kleinstein, yes, you're getting some idea that they're different, but without them updating the datasheet or die analysis it will be hard to tell for sure.Maybe I'll probe resistance between these GND pins to see if it reveals something.BTW, here is a day 2 of 115C aging test. It lost ~2.5ppm over second 24 hours.Initially it was relatively stable, but as you can see, later the obvious popcorn noise started to appear.Noise amplitude is ~0.3ppm short term and up to 0.5ppm worst case over 15 minutes.How that is related to the oven temperature is yet to be determined.

author: iMo
author_rank: Super Contributor
timestamp: October 21, 2024, 04:27:55 pm
content: Interesting:QuoteIt looks like there are only couple of discreet Temperature setpoints..

author: iMo
author_rank: Super Contributor
timestamp: October 22, 2024, 12:05:41 pm
content: Quote from: Kleinstein on October 21, 2024, 08:07:07 amThat may work with the ADR1001 too, there are 2 grounds (2 separate bond pads and bond wires on the same internal GND trace) for the reference part as well afaik..

author: laichh
author_rank: Regular Contributor
timestamp: October 23, 2024, 02:32:02 am
content: Quote from: iMo on October 22, 2024, 12:05:41 pmThe die picture by Richi's Lab shows exactly that.https://www.richis-lab.de/REF29.htmThe above picture was taken from 2022 ADR1001 engineering sample. Mass production ADR1001 chip in 2024 shows the same too.https://www.richis-lab.de/REF45.htm

author: dlebed
author_rank: Regular Contributor
timestamp: October 26, 2024, 07:08:55 pm
content: I got all the pieces and this is how the reference box supposed to look like (screws will be changed to nylon) + the PCB bridge was cut.I ran ~100 on-off cycles (15 min on @115C, 5 min off) to see what level of hysteresis is there and if it will level off with time.There is a clear change in output voltage and it drifted upwards (vs downwards aging drift) by about 1ppm.Upd: with an extended stack height the total power consumption is down to 0.46W @ 15V in open air at 25C ambient and 115C heater setpoint.Adding intermediate polyamide (flex PCB) separator in the middle (as shown in photo saves ~3% power).

author: dlebed
author_rank: Regular Contributor
timestamp: October 26, 2024, 08:02:01 pm
content: And here is one last update on the output impedance.Unfortunately, I don't have sense/force GND separation as the pin mapping is unclear so far, so there is ~0.04 Ohm trace impedance contribution in the measured values.So, it's pretty clear that the output impedance is about 0.8 Ohm for loads up to 7mA.

author: iMo
author_rank: Super Contributor
timestamp: October 26, 2024, 08:42:43 pm
content: I measured roughly 0.008 Ohm (1mA) at ADR1001 buffer's output set to 5V and 1.7ohm at 10V (that 1R7 was lowered in the latest chip revision).

author: dlebed
author_rank: Regular Contributor
timestamp: October 27, 2024, 12:17:59 am
content: Well, REF80 is not as bad as ADR1001 10V output was implemented initially, but not really great. So a buffer opamp most likely will be needed if any kind of load needs to be driven by REF80's output.Here is also an update on humidity sensitivity.I made a quick check by first placing the reference over the boiling water for ~30 minutes.Obviously, the PCB was saturated with water after that, but it might not be enough for water to penetrate the REF80's package deep enough.After that I powered it for an hour with the same 115C heater temp and it stabilized at a value that is within 0.5ppm of what it was before the exposure to humidity.Since I saw a popcorn noise at some points that could make output jump up to 0.5ppm peak-to-peak, I would not say that humidity exposure make any measurable change to the output voltage.I could imagine that many cycles of temperature and humidity cycling could affect it, but it's quite hard to to automated humidity cycling at home.Here is the startup graph with board being soaked with water vapor. Ambient RH is ~37%.

author: Andreas
author_rank: Super Contributor
timestamp: October 27, 2024, 07:37:57 am
content: Hello,it takes weeks, not hours until you can tell something about humidity.Look for acrylpolymers which are used in humidors to generate a high humidity environment.with best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: October 27, 2024, 07:45:13 am
content: The ceramic case of the REF80 should not have a direct effect from humidity. The point is humidity in the PCB causing mechanical stress and that effects the reference. 30 min in the steam is some time for humidity to enter, but it may still not be saturated even though things get faster at high temperature.The higher temperature at the ref. chip below the reference also speeds up the recovery. This can be a plus for the heated ceramic case. The humidity effect would settle relatively fast. Closer to room temperature the time constant is otherwise more in the days to weeks. It may still take a little longer before the humidity effect is fully settled.With the sensitive part heated quite a bit the room temperature RH should not make much of a difference. Heating the PCB by some 60 C would lower the RH seem by the PCB by about a factor of 60. A similar factor is expected for the speed up of the time scale.For low RH sensitivty is can really help to have the link to the opposite PCB side cut, so that stress from the outer, cold PCB part would have very little effect. The difference in the drift from the initial phase and after mounting the heat shield could be from cutting that link.

author: iMo
author_rank: Super Contributor
timestamp: October 27, 2024, 09:04:32 am
content: But still, the largest contributors to the TC/humidity/stability will be the external resistors for scaling to 10V or 5V or 2.5V, if required. A pity TI has not put 2 or 4 those resistors on the chip as well to be hermetic and ovenized..Another product knitted with a hot needle, imho.. Both REF80 and ADR1001 are the competitors in the hot needle knitting competition..

author: dlebed
author_rank: Regular Contributor
timestamp: October 27, 2024, 07:32:44 pm
content: Kleinstein, that was exact my thinking.Just by looking at it, it seems that boiling water vapor is quite successful in saturating the FR4.I'll need to do a weight test next time to see how much water vapor is trapped inside.I did another ~50 rounds of on-off cycling over 12 hours after exposure to 100% humidity and I don't see any long-lasting hysteretic effects so far.The overall drift is ~0.4ppm p-p, with it returning to the starting point with <0.1ppm accuracy.iMo, to me there is still certain advantage as you can place many of these REF80/ADR1001 in parallel and then put an expensive gain-setting resistors only once at the final output.BTW, any thoughts on whether added buffering before averaging does provide any benefit in parallel reference configuration?Even REF80 has significant output impedance (0.8Ohm) and paralleling them (with ~100Ohm series resistors) will affect its output, as long as that output impedance is stable and the offset stays the same, I'm thinking that additional buffering before averaging might not provide much benefit...In this case, you only put a single buffer after averaging and you only put one set of precision resistors to derive all the other voltages.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 27, 2024, 08:52:04 pm
content: There is probably no need for an extra buffer before averaging. How sensitive the averaging to the stability of the resistors depends on the difference in the voltages. The preliminatry specs call for relitively tight tolerance and thus not so critical resistors. On could probably also use more than 100 ohm for averaging and also use the resistance for some RC filtering. So have a capacitor to ground after the resistors.I think it is a bit early to think about averaging. First one may want a little more real world experiance with noise, drift and hysteresis. Averaging can help with noise, but it would not help much with residual TC, hysteresis or common drift.For testing hysteresis from on/off cycles one may have to use a bit longer. 15 min may be just enough for the on time - at least this is judgeing the recovery after the humidity test. It may still need a little more to really see and average the final voltage a little more.The off time is at lower temperature and thing happen slower that. So a real hysteresis test would need much longer off phases, more like 12 hours off. The fast turn on/off testing is more like checking if there is some long term change from many cycles. Just 5 min off may not even be enough to really cool it down all the way.Having individual sclaing resistror can have some advantage too: one could see of different units behave different (e.g. detect more random drift components). It would also allow mixing different reference types with there different voltage. The nice and stable temperature helps for the TC and also the humidity effect, but the rather high temperature acceperates aging. So resistors on the heated chip are a 2 sided thing.

author: floobydust
author_rank: Super Contributor
timestamp: October 28, 2024, 03:15:51 am
content: I am just wondering- why run this ref so hot? I understand a stable temperature is paramount, above highest room temp expected but this seems problematic:REF80 "TSETmust be programmed to 45ºC above the max ambient temperature to make sure that the heater is regulating the temperature properly.""Operating Temperature Range 0ºC to 70ºC, TSET115ºC" {which is pin left floating}But this is not being run outdoors in Saudi Arabia!TSETresistor 800kΩ gives 85ºC.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 28, 2024, 07:11:36 am
content: The temperature is rather high. The 45 deg. above ambient is needed as the device has quite some power consumption on its own from the high zener current. How much headroom is actually needed depends on the thermal design / PCB - it may be even more with good isolation.For the initial testing it helps if the temperature is high and thus many of the effects faster. This may include some noise part (e.g. popcorn like noise). Here faster can be better: shifting noise to higher frequencies, away from the really slow part (e.g. < 0.1 Hz) where it really matters.It could also help for a burn in.For a final use a lower Tset setting may still the better option. Even 85° C is not that low. Still below the 95°C found in LM399 and the LTZ1000 in the HP3458.From the limited data it looks like the REF80 may be good for long term stability, though not so much with the noise.

author: iMo
author_rank: Super Contributor
timestamp: October 28, 2024, 07:47:32 am
content: The zener's power loss may add 15C max.40C inside a meter at 23C ambient could be fairly normal, afaik, with max 35C ambient in a hot day you get close 60C at the zener. Add the 15C min as the ovenizer margin and you get 75C I would set (btw. 70C is the default setting in ADR1001).REF80 allows only 4 temp settings it seems - 115C, 105C, 95C, and 85C (ext resistor value insensitive).ADR1001 allows a cont. range from aprox 40C to 125C (ext resistor value sensitive)..Resistors - with 9 NC pins you may add a large variety of resistors and/or dividers for various voltages on the chip. The output buffer is not that critical to be there. TI should really think about that, otherwise people will not see a price advantage when using the REF80.PS: or a single divider which resistors might be programmable via fuses. You may get 6 bits for the programming (9NC pins -> 3pins for the divider and 6 programming bits == 63 divider ratios??).Or an SPI/I2C interface for an unlimited functionality

author: Kleinstein
author_rank: Super Contributor
timestamp: October 28, 2024, 10:16:38 am
content: The design by delebed seems to be at some 160 K/W (https://www.eevblog.com/forum/metrology/ref80-a-competition-to-adr1001/msg5683639/#msg5683639). With 225 mW of power (15V) this would be more like 36 K of temperature rise from the zener part. Even with 10 V supply one would still have some 24 K above ambient. The 45 K number would have a bit more reserve for even better isolation, higher current and maybe 1 K as actual headroom for the regulator / heater. It is a bit unclear how for down the heater actually works, there could be some 1 mA of min current as well.15 K temperature rise may be for the PCB without cuts.Quite some cut out and thin traces are kind of a requirement for practical use, to reduce PCB stress and keep the power and thus termal gradiens small.I would consider some 70°C as the lower practical limit, as 40 C ambient and 30 K reserver for self heating.I am a bit surprised to not have a lower set temperature option. At least for a well controlled lab environment it could make some sense.

author: iMo
author_rank: Super Contributor
timestamp: October 28, 2024, 06:41:13 pm
content: Yep, you are right, as usual.. But my 15C off the zener (the zener diode itself = 15mA*7.6V) is not much off as well..

author: dlebed
author_rank: Regular Contributor
timestamp: November 02, 2024, 08:13:10 pm
content: I'm continuing filling the characterization gaps from datasheet.Here is a comprehensive picture on thermals.My final physical "reference cell" design (with PCB bridge cut and it fully enclosed) gives thermal resistance of θJA of about 190-195 °C/W (25C ambient data):- Total power consumption at 115C oven setpoint is 15V * 0.031A = 0.465 W (θJA = 194 C/W)- Total power consumption at 85C oven setpoint is 15V * 0.021A = 0.315 W (θJA = 191 C/W)- Power difference between 115C and 85C setpoints is 0.15W, θJA = (115 - 85) / 0.15W = 200 C/WI'm pretty confident with that numbers and results looks promising and it is clearly better than ADR1001's EVK with only 140 C/W of thermal resistance.I also ran it without power supplied to heater (only zener power was on).It burns about 16mA no matter what supply voltage is (expected).Here are some thermal images for comparison (NB measured without top insulation, so thermal resistance will be a bit lower in this case).Without heater, 16mA @ 15V (0.24W), max package temp is ~62CWithout heater, 16.5mA @ 10.5V (0.17W), max package temp is ~51CWith heater, 85C oven setpoint, 21mA @ 15V (0.315W), max package is ~71CSo with all of that said, if you supply zener with ~10V, that will result in ~0.17W, with θJA = 190 C/W, that will result in junction temp of ~57C at 25C ambient.Heater will burn another 0.145W to get to 85C setpoint.The only thing that is unknown is what is quiescent current of heater circuit. If that's low enough, then we can assume that at 25C there is about 25C margin for heater regulation at 85C setpoint.Also, one note on the mechanical stress from the PCB.As floobydust shared before, ceramic package CTE: is about 5 to 7ppm/C and I ordered PCBs from OSH Park and they use Kingboard KB6167F for their normal boards, which has quite low (for FR4) X/Y CTE of 12/15 ppm/C.This means that that the difference in CTE is in 5-10 ppm/C range and the paper floobydust shared states that if CTE mismatch is within 5ppm, then no issues should be seen, so with good FR4 we're borderline OK in terms of mechanical stress from the PCB.I also noticed that OSH Park's "After Dark" boards has even lower TCE of 11~12ppm/C (Ventec VT 447 b substrate),https://docs.oshpark.com/resources/afterdark-substrate-Ventec-VT-447-b.pdfI probably will go with "After Dark" option for final version, I also like the way it looks.P.S. I got 0.8mm 2oz copper boards, will soon test them to see if there is any difference in thermal resistance between 1.6mm 1oz and 0.8mm 2oz.

author: branadic
author_rank: Super Contributor
timestamp: November 03, 2024, 01:40:20 pm
content: Here is my comment on CTE and CTE mismatch:Goal number one for any kind of circuit board is that the CTE of the substrate matches that of the conducting material, otherwise your copper would peel of your FR4 board very quickly. For FR4 this is achieved only in x/y direction, while FR4 shows 4x to 5x higher CTE in z-direction, the reason why boards tend to fail on vias over large temperature excursions.However, as a rule of thumb a CTE mismatch between two materials of <10 ppm is said to cause no trouble in terms of reliability in a certain temperature range (typically -40 ... 85 °C), which does not mean that it doesn't induce stress, which itself can be transferred to whatever stress-critical component you are looking at, in your case the reference die.Having said that, be careful with general statements.-branadic-

author: dlebed
author_rank: Regular Contributor
timestamp: November 03, 2024, 05:59:40 pm
content: branadic, agree, the TCE mismatch issue has many dimensions to it.With copper TCE of ~17ppm/C, FR4 XY TCE of 12-15ppm/C and ceramic substrate TCE of 5-7ppm/C things look more of less fine in XY direction. FR4 is kind of in the middle between copper and ceramic substrate and the difference is not so drastic.You made a good point about vias, though if you look at laminate datasheet, FR4 actually has two TCEs (before Tg and after Tg) and after-Tg TCE is much higher (~200ppm/C vs ~40ppm/C before Tg).It might be a good idea to get rid of all vias around the REF80/ADR1001 just in case.https://docs.oshpark.com/resources/two-layer-substrate-Kingboard-KB6167F.pdfTo me, that means more problems with soldering and not during its use, as long as you don't run components at 150C.Much of the physical stress should result from cooling after soldering (180C -> 25C transition).Reference heating should only help reduce the stress as it gets closer to the point where solder solidified.If you expose the board with reference in ceramic package to temperatures below freezing while unheated, I could see how that could create troubles.That's why I tried to do ON-OFF cycling to see if it will help removing any mechanical strain that might remain after soldering.I was doing 15min ON - 5min OFF cycling to my REF80 for 2-3 days and there are no reliability or drift issues after ~200 cycles so far.

author: dlebed
author_rank: Regular Contributor
timestamp: November 03, 2024, 06:43:58 pm
content: Unheated tempcoI made a few measurements of the unheated tempco of REF80.Spoiler: unheated tempco is about -4ppm/CFirst, I disconnected heater (set to 115C) supply and saw the voltage rise by ~145ppm.My estimates are that the junction temp dropped by 45C, from 115C (heater on) to ~70C (self-heating from 15V * 16mA = 0.24W).This results in a tempco of 145ppm / -45C = -3.2ppm/CHere is the graph showing voltage change after heater supply was disconnected.Here is also a close-up of stabilization right after heater was off. You can see some 0.5-0.7ppm jumps, probably because of thermal stress and thermal equalization going on.All of these sudden 0.5ppm jumps subside within ~10 minutes after turning the heater off and there are no more of such jumps seen over next 24 hrs of running it unheated.After that I changed heater setpoint from 115C to 85C and measured the voltage.Voltage went up by 138ppm when heater setpoint was lowered by 30C (who knows what the accuracy of heater setpoints is), which results in -4.6ppm/C of tempco.Two measurements from above are not too far from each other, so unheated tempco could be assumed to be about -4ppm/C, which is almost an order of magnitude better than ADR1001's datasheet spec of 36ppm/C.Things are starting to get interesting...Here is the plot of it running unheated for 24hr.TBH, my DMMs struggle to agree with each other to that precision...With 1C temperature swing, unheated REF80 output changed only by ~0.6ppm.It's hard to tell if heater circuit gets some power backfeed from the zener circuit and that's what gives it some amount of regulation (though I did not notice any changes in power consumption with it unpowered),or there is some additional thermal compensation going on internally.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 03, 2024, 07:43:27 pm
content: The TC of the unheated ref. voltage is not necessary constant which means a nonlinear temperature voltage relation.With references that work by compensating a positive and negative TC part against each other it is well possible to get to a range where the 2nd order or even higher order parts get relevant. Low TC without heater , more from there to 115 C and even more for 85 C to 115 C would at least be consistent.The rather good TC without the heater is interesting and may indicate some trim to reach a low TC to start with. It could however also be a lucky unit.The steps in the set temperature may not be that accurate, but should still be a reasonable base for a TC measurement. After all it is really about the rough size, not an accurate number for the TC.For the stress between the ceramic case and PCB one has to take into account the the solder joints and to some degree als the FR4 can show stress relaxation. Especially at high temperature the material can not withstand a high stress and the stress can slowly go down. The reference runs relatively hot - enough to expect at least some stress relaxation.With some parts it made a difference that this effect tends to be slower with lead free solder compared to leaded solder. It at least was a concern for the transition to lead free and power cycle for computer chips that run relatively hot. So the type of solder alloy may make a difference.

author: iMo
author_rank: Super Contributor
timestamp: November 03, 2024, 09:19:14 pm
content: Could it be the REF80 contains some digital compensation circuitry as well??The 4ppm/C unheated sounds unbelievable..One indication might be the temperature setting is scanned at the power-on and set fixed till the next power-off, or, the another - "jumps plus minus 0.5ppm"..For that you would need some sequencer logic at least, imho.A combination of a digital compensation (ie. based on a lookup table and calibrated at factory - there are many NC pins for a programming) and the ovenizing on top of that would be a nice combo, indeed..Noopy can tell, sure

author: Noopy
author_rank: Super Contributor
timestamp: November 04, 2024, 03:54:53 am
content: Quote from: iMo on November 03, 2024, 09:19:14 pmI´m already monitoring the availability!

author: dlebed
author_rank: Regular Contributor
timestamp: November 04, 2024, 03:56:29 am
content: iMo, TI uses tempco compensation in their bandgap-based references, new TI's REF54 specified at 0.8ppm/C tempco:https://www.ti.com/lit/gpn/REF54"Due to temperature curvature correction to achieve low-temperature drift, the temperature drift is expected to be non-linear."It makes sense to add a piece of digital logic, calibrate it and then apply compensation, though in that case you probably 1 step away from providing exact 10V output, why not do that as well, if you anyway calibrating it and applying compensation?

author: dlebed
author_rank: Regular Contributor
timestamp: November 04, 2024, 05:29:42 am
content: Kleinstein, I checked heater power off behavior with another unit (Unit B is on 0.8mm/2oz PCB).Behavior is almost identical (change is ~158ppm vs 145ppm for Unit A), so, it does not look like only Unit A was a lucky one.The only difference is that this time it stabilized very smoothly, without any jerking.It's highly likely that all of my current REF80's are from the very same wafer, but you still could get different outcomes if dies are from different corners. Maybe they got a whole "lucky" wafer?BTW, the REF output voltage spec indeed seem to be very tight. Unit A vs Unit B output difference is only 450ppm (0.047%) or 3.4mV.Unit A is 7.5682526V, Unit B is 7.5648139V.BTW, there is another test I made: I ran supply voltage sweep from 10V to 16V with heater disabled.I did not record the current, but I did a spot check and it was fairly stable at about 16mA, this sweeps the power consumption (dissipation) from 0.16W to 0.25W.Assuming thermal resistance is ~200C/W, this power difference should result in ~20C die temperature difference for 10V vs 16V.There are two sweeps: first was long (10-16V, 0.1V step, 300 sec each), then quick (10-16V, 0.1V step, 60 sec each).The output difference is only ~13ppm p-p.In this scenario tempco seem to be even lower, around 13ppm / 20C = 0.65ppm. As you mentioned, tempco is non-linear and this sweep mostly covers Tj of around 50-70C.P.S. thinner PCB of Unit B (0.8mm vs 1.6mm) did not help with thermal resistance because it comes with thicker copper (2oz vs 1oz).As expected, thermal resistance seem to be ~5-7% worse compared to Unit A (1oz copper) as most of heat loses are carried over copper in my design. The only remaining thing to check is if there any difference in terms of mechanical stress for 1.6mm vs 0.8mm.I finally got a macro lens for thermal camera, here is a crisp thermal image of Unit B.

author: dlebed
author_rank: Regular Contributor
timestamp: November 04, 2024, 06:36:10 am
content: My final test for today is to run unheated reference with external heater as I don't have any climate chamber to run nice temp. sweeps.Plot shows data right from power-on, note how small the power-on settling deviation is (~5ppm).Test was as follows:1. Power on unheated reference with 10V power supply2. Let it stabilize sitting on a heat plate (heat plate is cold at this point)3. Turn on the heat plate and let it stabilize at 100C4. Let it sit at 100C for a couple minutes5. Turn off the head plate and let it slowly cool downTo me that initial overshoot followed by undershoot when heater was enabled looks like a control loop response.Temperature swing was 25C -> 100C and then cool down, having only ~110ppm p-p REF change over 75C span is quite impressive and it seems that there is some compensation going on internally.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 04, 2024, 09:03:51 am
content: It is somewhat likely that the chip uses some form of digital trim. Ti uses this with quite some new parts, e.g. with OP-amps like OPA205, OPA192. The discrete steps for Tset also points to some internal digital circuitry.This would be some one time adjustment as a last step of production. The main difference to laser trim is that it can be done after the case is closed and possibly even an initial burn in. I would only expect a crude trim of the unheated TC - though they may have gone a bit too far, possibly considering an unheated version and allowing fine adjustment may not be that much more effort.I don't see any way to have a TC compensation to automaticly adjust at every turn on - if at all it may take a little time for the set values to become active. However this should be more on the µs scale and thus too fast to see in the curve.The transient from turning on the heater could be an effect of temperature gradients from a rather fast warm up from one side. Regulator overshoot would be at the hot plate, not the reference.The step from 7.5 to 10 V would need long time stable gain, like good resistors. The digital correction could help with getting exactly 10 V when new and maybe a little with the TC (is anyway less an issue with the heater). However it would not help with long time drift. The gain adjustment would make stability even a bit more difficult.

author: iMo
author_rank: Super Contributor
timestamp: November 04, 2024, 09:21:38 am
content: Quote from: dlebed on November 04, 2024, 03:56:29 amProviding 10V output (or 5V or 2.5V) requires more laser-trimmed long time stable resistors and some opamps/buffers, perhaps that is the reason why they did not do it yet. One interesting thing is the temperature setting is not "linear" like the ADR1001 got, but only in 4 discrete steps (my understanding). And the Iz is set internally as well (in ADR1001 you set Iz with an ext. resistor). Like something inside - ie. the additional compensation - is adjusted for those 4 temp settings and Iz current only (actually 5 temp settings when counted the heater is off). But perhaps they only wanted to eliminate the TC influence of the external temperature and Iz setting resistors..PS: we may conspire here.. ..till Noopy gets the gadget under his scalpel..

author: dlebed
author_rank: Regular Contributor
timestamp: November 04, 2024, 05:14:27 pm
content: Kleinstein, yes, indeeed the undershoot part of plot is caused by the hot plate regulation (it was late yesterday and I somehow missed that).Initial overshoot is then could be just the way tempco behaves.

author: dlebed
author_rank: Regular Contributor
timestamp: November 05, 2024, 05:24:29 am
content: I was able to get one part sacrificed to be able to figure out actual pin functions.Here comes the "low resolution" die photo. Is there anybody who has equipment to make better die photos in the US?Meanwhile I'll try to see what I can do to get higher resolution photos. Any hints are appreciated (that's my first die photo, will try to play with polarizer).

author: Noopy
author_rank: Super Contributor
timestamp: November 05, 2024, 05:45:24 am
content: I want to take pictures!!!But I'm located in Germany... :'(

author: floobydust
author_rank: Super Contributor
timestamp: November 05, 2024, 05:47:43 am
content: Ahhh all that gold. And a few N/C pins are bonded out pin 1,2,6 I think. Hmmm.Three fat wires across the middle of the die... ? edit: this surely must put TCE stress on the die due to the dissimilar materials.Anyone see glass spheres? Is the lid magnetic?

author: Andreas
author_rank: Super Contributor
timestamp: November 05, 2024, 05:53:56 am
content: Hmm,does not look to be symmetrically regarding the heater:it would be interesting wether the chip output voltage is sensitive to tilting (orientation in room) like the LM399.with best regardsAndreas

author: dlebed
author_rank: Regular Contributor
timestamp: November 05, 2024, 06:10:44 am
content: This is probably the best I can do for today.

author: dlebed
author_rank: Regular Contributor
timestamp: November 05, 2024, 06:11:17 am
content: And side view...

author: iMo
author_rank: Super Contributor
timestamp: November 05, 2024, 06:23:02 am
content: Quote from: floobydust on November 05, 2024, 05:47:43 am1,2,6 are NCs wired out..4,5 - 2x 2bond wires - ref_out - perhaps S and F?The 3 diagonal look like groundThere are 4 die pads similar to ref_out not bonded - perhaps the second output voltage?Interesting the 4x13 structures in the middle..Much more detailed shots would be required to see the digi parts, if any..

author: dlebed
author_rank: Regular Contributor
timestamp: November 05, 2024, 06:24:32 am
content: floobydust, yep, tons of gold, actually the solder is also 80% gold, seehttps://www.ti.com/lit/an/slvaeu0/slvaeu0.pdfQuoteI don't see any glass spheres TBH, maybe they're way smaller than on ADR1001, who knows.And the lid is magnetic, yes.

author: dlebed
author_rank: Regular Contributor
timestamp: November 05, 2024, 06:30:47 am
content: Isn't that look like a digital logic?BTW, I measured "diode" voltage across different pins and pins 14-15 (REF_GND) are dead short, but pin 13 (GND) connection to pins 14-15 is not so simple, it's 0.473V in one direction (GND+, REFGND-) and 0.63V in reverse direction at 10uA current.

author: iMo
author_rank: Super Contributor
timestamp: November 05, 2024, 06:45:37 am
content: On the first glance it seems there must be digital logic, simply because the temperature setting mechanism (the external resistor is "sampled" with comparators or a simple ADC and the value has to be memorized then in some digi logic). The digi compensation would require a sequencer or a small MCU as well, if any. There could be anything on the chip when made with small enough node..

author: Kleinstein
author_rank: Super Contributor
timestamp: November 05, 2024, 10:20:33 am
content: The digital compensation / trim would not need a sequencer or so. One would still need some form of a seriel interface to program / trim, but for the later function it would work like some digital trim pots or DACs, likely with a write once memory directely connected. So the DAC/digipot setting are written once during a trim step and than stay the same all the time (except for the set temperature one).The are still quite a lot of structures. So there could be addional functions (some may not work as planed) and likely also test structures.The additional 4 bond pads and struckture around look really very much like the output - so maybe a 2nd amplifier output of some kind.Pins 1,2 and 6 that are NC but bonded out may well be for the trim program step.The 2x2 bond wires are still odd. If the 2 pins (4+5) are sense and drive this would not make much sense. If the have drive and sense seprate for pins 4 and 5 this would be quite some effort and a possible offset between the 2 outputs would be an issue. The 4 pads still look separare, not a single large area.The glue to attack the die looks like it has struckture inside - so glass beads are possible, just to small to resolve.

author: dlebed
author_rank: Regular Contributor
timestamp: November 05, 2024, 05:04:09 pm
content: This is official, the part will go to Noopy for further microscopical investigation

author: magic
author_rank: Super Contributor
timestamp: November 05, 2024, 05:48:54 pm
content: Quote from: dlebed on November 05, 2024, 06:30:47 amYep, what you see here are densely packed north-south traces in the top layer, and the layer below should be west-east.Looks like typical CMOS logic with plenty of transistors there.

author: floobydust
author_rank: Super Contributor
timestamp: November 05, 2024, 06:01:56 pm
content: A digital compensator could be a synchronous state machine, meaning there is a clock oscillator somewhere. I don't think they're using just combinational logic.I dislike the three fat jumpers, gold CTE is 14.2 and I would expect the die to see a little strain from those, across the diagonal.dlebed thank you for taking off the lid, to help let the genie out of the bottle

author: Kleinstein
author_rank: Super Contributor
timestamp: November 05, 2024, 07:00:37 pm
content: The diagonal gold wires would not cause much stress: the wires are bend and can thus move with relatively low force. The Ref chip run at an essentially constant temperature and thus a constant stress. Gold is relatively high melting point and not showing much stress relaxation at moderate temperature.It is till odd to have the gold wires over the chip.For normal operation there is no need for any clocked operation - just combinatorial should be enough to just check if there is a possible adjustment for the trim settings. This could be permanently disabled after programming it anyway.

author: iMo
author_rank: Super Contributor
timestamp: November 05, 2024, 07:28:38 pm
content: My guessThere are 4 heaters around a block of "13_zeners_with_ser_13_diodes" in parallel (a naive assumption coming from the "standard 7V+0.6V model" perhaps), a temperature setting machine and the oven control (with perhaps a digi temp compensation), on the left is a dual opamp output buffer (for two output voltages)..

author: Noopy
author_rank: Super Contributor
timestamp: November 18, 2024, 04:49:48 am
content: Now let´s take a closer look.The designation of this REF80 begins with an X, which indicates that it is an engineering sample.Of course you know the pinout.Here we can see that the reference potential is routed to the two contacts of the package with two bondwires each. The NC contacts 1, 2 and 6 are also connected to the die.The three bondwires running from top left to bottom right on the die are very striking.Balls were first bonded to the lower right bondpads of the transverse bondwires and the bondwire was immediately cut off again. The bondwire was then attached to a bondpad at the top left with a ballbond and guided to the bottom right. The wire was then attached to the ball with a wedgebond. This procedure is necessary because wedgebonds cannot be applied directly to bondpads without further ado.The thermal conductivity coefficient from the die to the package is not yet specified in the datasheet. A high thermal resistance would be desirable so that the temperature of the reference is influenced as little as possible by temperature fluctuations in the environment. At first glance, the material used to attach the die to the package could be a polymer. In detail, however, the surface looks rather metallic.The edge length of the die is 1,8 mm. On the surface, there are testpads in two sizes in addition to a few uncontacted bondpads. One of the testpads is only slightly smaller than the bondpads. On closer inspection, there are a few very small testpads, especially in the upper area.Both images are also available in higher resolution:https://www.richis-lab.de/images/REF01/51x08XL.jpg(43MB)https://www.richis-lab.de/images/REF01/51x09XL.jpg(54MB)A very angular Texas Instruments logo is shown in the top left-hand corner of the die. The same applies to the copyright symbol in the bottom left corner. The design is obviously from the year 2023. In the upper right corner, the characters A11100 are shown in different layers. The REF80 actually appears to have 6 metal layers. Accordingly, each character could stand for the revision of a metal layer. The character sequence REF8014 in the bottom right-hand corner could represent an internal designation.The REF_GND potentials are treated very differently on the die. Pin 15 is routed further into the center of the circuit, while pin 14 contacts a bondpad at the edge. The GND potential is located directly underneath.You can see in detail that the two REF_Z potentials on the die are also processed separately. The two upper bondpads (pin 4) are connected to a wide line. The two lower bondpads (pin 5), on the other hand, only contact a thin line. The upper two bondpads are probably connected to the output driver and the lower two bondpads form a feedback path with which the voltage can be regulated directly at the output pin. Between the left two bondpads there is a structure that could be a resistor. At least such a connection would be logical in this context.A group of four bondpads is placed in the bottom left-hand corner of the die, which are very similar to the REF_Z bondpads in the top left-hand corner. Here, however, all four bondpads are connected to each other. Nevertheless, there is also a structure between the two left-hand bondpads as with the REF_Z contacts. The purpose of these four bondpads remains unclear.As the REF80 is very complex, many structures and potentials cannot be assigned. The REF_GND potential is routed to the other corner of the large structure in the middle of the die with a bondwire. It is clear to see that great importance has been attached to symmetry in this area. The output driver of the REF_Z potential is also transmitted to the opposite corner. The REF_Z feedback leads a thinner line to the thick frame surrounding the central elements. There are four identical blocks in the center of the die.Each of the four central blocks consists of three different elements. There are 2 round elements and 14 larger rectangular elements, with one of these rectangular elements placed slightly to the side. It is not possible to say with absolute certainty, but it seems quite plausible that the two round elements are buried Zener diodes. The metal layer gives the impression that the two Zener diodes are connected in series. The rectangular elements could then be the bipolar transistors that compensate for the temperature coefficient of the Zener diodes. The transistor placed slightly to the side could then be used for temperature measurement.It could be that four of these reference voltage sources have been integrated in order to connect them in parallel and thus reduce the noise. However, given the complexity of the REF80, a more complicated mode of operation is also conceivable.The four brownish elements in the bipolar transistors could be the emitter surfaces.Bondwires run over the Zener diodes in the center of the REF80, which is why it is difficult to depict them optimally. However, several of these elements are integrated on the die. In the center is a round structure surrounded by four frames in the various metal layers.It appears that free areas in all layers have been filled with dummy structures. This is necessary to ensure that manufacturing processes affect the surfaces as evenly as possible. At the same time, however, it is noticeable that recesses have been made in these dummy structures above many circuit elements.The heater lines run from the bondpads to the central structures, where they form a frame. It is not possible to see where the heaters themselves are located, but it can be assumed that they are arranged symmetrically around the central elements.Large resistance surfaces are integrated in the left-hand area of the die. At first glance, it appears that a laser alignment has taken place there. However, a closer look reveals that the patterns on the resistors are not the traces of a laser. Stripes of a different layer run under these resistors.Several differently constructed resistors can be seen here.There are a large number of thin, vertical lines on the left-hand side of the die. Horizontal lines can be seen in the layer below. It could be that a control logic is located here.The low-lying lines seen here appear to be dummy structures. However, they are surprisingly inhomogeneous.Here, the dummy structures in the top layer have been generously omitted over two elements, but the dummy structures are still present in a deeper metal layer.Some recesses are very small. The small structures there are difficult to image sharply.https://www.richis-lab.de/REF46.htmI haven´t touched the REF80 yet. What should we do?1) Nothing - sometimes waiting for new things to do is not the worst idea.2) Strip the bondwires and clean the die to get better pictures - probably not necessary3) Strip the layers - I can´t do real delayering but I can strip everything down to the substrate. Of course after that it is dead.4) After 3) we could try to analyse the die attach "mechanicaly".

author: dlebed
author_rank: Regular Contributor
timestamp: November 18, 2024, 05:30:10 am
content: Finally, Noopy, you did a great job!After looking at GND connection, I believe now I have idea about the pin roles.It seems to me that:- REF_GND (15) is FORCE- REF_GND (14) is SENSE- GND (13) is power GND for Zener supply (connected to GND circle running at the edge of the die)As I mentioned before, resistance between two REF_GND pins is < 1 Ohm, so they're shorted on chip.GND (13) is a separate pin and is not directly tied to REF_GND.As for the next plans, what about soldering it on a board and probing unbonded pad voltages (before destroying it)?Maybe at least 4 big ones that resemble REF_Z ones...

author: iMo
author_rank: Super Contributor
timestamp: November 18, 2024, 07:29:31 am
content: Yep, try to run it and perhaps we will see the light show..Great pictures!PS: is that shot with your new uscope?

author: Noopy
author_rank: Super Contributor
timestamp: November 18, 2024, 07:46:04 am
content: Quote from: dlebed on November 18, 2024, 05:30:10 amThanks!Quote from: dlebed on November 18, 2024, 05:30:10 amI agree with you. Except with pin 13. Or at least I´m not sure about what you wanted to say. In my view pin 13 is more for dirty things like logic supply.Quote from: dlebed on November 18, 2024, 05:30:10 amUnfortunately I can´t probe the die. I could try but usually the pads are to small (for me).But I´m not sure it will help much. I assume the "additional REF_Z contacts" are inactive since they are shorted together. I assume you would need a different mask set for activating them.Quote from: iMo on November 18, 2024, 07:29:31 amThanks!Unfortunately I can already tell you that there is no light in the REF80. :'(I powered it up and took a very long exposure just to see if there is any light anywhere but everything was dark black.Perhaps there is not enough current/light or the huge amount of layers are damping it too much.Yes, that´s my new optical equipment and here it is really necessary.

author: iMo
author_rank: Super Contributor
timestamp: November 18, 2024, 07:58:18 am
content: No light may mean the zeners are ideally made, no defects, no impurities, no recombination centers..

author: dlebed
author_rank: Regular Contributor
timestamp: November 18, 2024, 08:14:38 am
content: QuoteNoopy, well, after reading the REF80 datasheet again, you might be right (unless they've messed up with pin definitions in datasheet).I made a different version of board to bring all the GND pins separately and reveal where the Zener current flows (according to datasheet it should be pin 15).We'll see what's going on in a couple of weeks once I get the boards back.

author: dlebed
author_rank: Regular Contributor
timestamp: November 18, 2024, 08:30:09 am
content: Update on tempco.I put my first reference (85C heater setpoint) into enclosure and added LDOs to make power clean and stable.I put a heater under enclosure (pure convection - without physical contact), let it heat up, then turn off the heater.Enclosure temperature changed by 15C (23C .. 38C).VREF changed by 2.8ppm, resulting in -0.18ppm/C tempco. It's on the higher side, but still within datasheet spec of max 0.2ppm/C.My setup does not have any fancy pure copper connections though, mostly gold-plated banana plugs +Pomona tellurium copper binding posts.The good news is that the VREF returned to the same point where it started to within 0.05ppm, so it seems the entire device does not have any apparent hysteresis.Here is the VREF output change over time.And here zoomed baseline voltage and return to it.

author: lichen867
author_rank: Newbie
timestamp: November 18, 2024, 09:36:19 am
content: a couple of weeks....in China, usually i draw the PCB file tonight, and send to JLC, then i will get my PCB on my desk at night the day after tomorrow. ..and total cost 2.5 $.

author: Noopy
author_rank: Super Contributor
timestamp: November 18, 2024, 02:29:28 pm
content: Quote from: iMo on November 18, 2024, 07:58:18 amOh, so they have built perfect zeners? Nice!

author: AnalogTodd
author_rank: Regular Contributor
timestamp: November 18, 2024, 03:17:15 pm
content: Quote from: Noopy on November 18, 2024, 02:29:28 pmThe perfect fab has finally been achieved! {/sarcasm}Yeah, I'd be willing to bet that with six layers of metal the light is just being blocked.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 18, 2024, 04:26:17 pm
content: The 2 round spots really look like 2 diodes in series. 2 Zeners in series would be a bit odd, as this would need zener diodes with much lower voltage ( < 4.8 V) that have a negative TC. This would mean a very different configuration, like 2 x 4.2 V Zener and a PN junction subtracted.The zener diode part could has well be hidden in the center, under the large metal top layer.

author: Noopy
author_rank: Super Contributor
timestamp: November 18, 2024, 04:57:04 pm
content: I agree with you.The whole circuit is insanely complex compared to the LTZ1000 concept. God knows what TI did to achieve the specs.As soon as we are sure that there is nothing more to look at, I can strip the upper layers. Perhaps we will see what is covered by the metal layers.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 18, 2024, 06:17:11 pm
content: Part of the complexity is likely some digital trim parts. So some shift registers, non volatile memory and DACs (possibly string DACs). The set temperature is also set digital from an initial resistor reading.Even the TC without the heater seems to be quite good and thus suggests already some trim here.The LTZ1000 also still need 2 external OP-amps - so that part is only the simple part.

author: iMo
author_rank: Super Contributor
timestamp: November 18, 2024, 06:31:04 pm
content: When you open and look/zoom deeply into that 53MB large jpeg you may clearly see several 8bit and 12+bit buses running on various places.. Looks like there is the logic everywhereThere are large greenish circles everywhere inside that large metalisation in the middle where we expect the zeners - what is that?

author: floobydust
author_rank: Super Contributor
timestamp: November 18, 2024, 07:03:50 pm
content: TI patent pendingBuried zener diode voltage reference with digital correctionbut they show it for a battery pack cell monitoring application? I can't see that level of precision required there, or the strain gage etc. it seems over hyped.But it shows how they do it.

author: Noopy
author_rank: Super Contributor
timestamp: November 18, 2024, 07:29:51 pm
content: Quote from: Kleinstein on November 18, 2024, 06:17:11 pmWell you are right, nevertheless, the REF80 looks extremly complex.Of course it´s understandable and as long as the specifications are ok, why not. Nevertheless...Quote from: iMo on November 18, 2024, 06:31:04 pmI have seen these circles too. It´s hard to say what we see here.Quote from: floobydust on November 18, 2024, 07:03:50 pmLooks interesting. I will have to take a closer look...

author: Echo88
author_rank: Frequent Contributor
timestamp: November 18, 2024, 09:00:26 pm
content: So many NC pins and digital logic, is there a chance it can run Doom?

author: iMo
author_rank: Super Contributor
timestamp: November 19, 2024, 08:42:47 am
content: You may try to look at the Vcc line with an oscilloscope. When the MCU inside is running you will see some activity on the line (the Icc current will change with the activity, remove any capacitors on the Vcc line if any).Like put there into the Vcc a small value resistor, say 50ohm, and watch the voltage on it (perhaps XX millivolts - it could be you would need to use an amplifier, you may couple it directly via a 50ohm coax, the o'scope input best set to 50ohm, be careful - not to blow up the 50ohm input).. Do power the REF80 from a battery such it is floating against the o'scope..PS: It is called "Glitching" or "Side-Channel Analysis"..

author: magic
author_rank: Super Contributor
timestamp: November 19, 2024, 09:25:41 am
content: Quote from: floobydust on November 18, 2024, 07:03:50 pmThe circuit of fig. 2 produces an output voltage lower than zener voltage, so at 7.6V nominal output the latter would need to be unusually high. That being said, this topology can work with any zener voltage higher than 5V (positive TC) so it's not impossible.Those PTAT generators are also quite noisy, but a 7V zener is 10x less sensitive to that than a bandgap reference.

author: Noopy
author_rank: Super Contributor
timestamp: November 19, 2024, 07:22:52 pm
content: Quote from: iMo on November 19, 2024, 08:42:47 amI could try to measure the current but I would prefer some optical analysis.Without the metal layers we would see how much logic is there.Quote from: magic on November 19, 2024, 09:25:41 amBut the supply voltage of the REF80 is allowed to be as low as 10V. So if there are two zener diodes in series each will have to be below 5V. ...and I don´t think they integrated a boost converter.

author: iMo
author_rank: Super Contributor
timestamp: November 19, 2024, 07:50:41 pm
content: Quote from: Noopy on November 19, 2024, 07:22:52 pmYou have to acquire an ion beam etcher to get rid of all those small squarish dingsbums hiding the logic..

author: Noopy
author_rank: Super Contributor
timestamp: November 19, 2024, 08:01:02 pm
content: Quote from: iMo on November 19, 2024, 07:50:41 pmI think I need some bigger donations...But the complete delayering usually shows some interesting structures too.

author: floobydust
author_rank: Super Contributor
timestamp: November 19, 2024, 08:56:23 pm
content: I think there's a clock oscillator running inside it somewhere. The output noise might show a spur if an FFT is done on it, with the output cap removed.

author: daqq
author_rank: Super Contributor
timestamp: November 20, 2024, 08:30:49 am
content: Quote from: iMo on November 18, 2024, 06:31:04 pmIt would be funny if you connected the unconnected bondpads, and got a nice SPI driven DAC with an OTP memory

author: Kleinstein
author_rank: Super Contributor
timestamp: November 20, 2024, 08:49:15 am
content: I don't see scratches on the unused bondpads. So they were likely not used for testing. Chances are high the trim process is via the 3 NC labeled pins (and maybe also some otherwise used ones) that already have a bond wire. The point of digital trim is that it can be done after the package is closed and if needed a short initial burn in / tempering. SPI like interface, OTP memory and DACs is definitely what I would expect.

author: Noopy
author_rank: Super Contributor
timestamp: November 20, 2024, 12:25:16 pm
content: Quote from: floobydust on November 19, 2024, 08:56:23 pmYes, since there is logic there is probably also a clock generator.Quote from: Kleinstein on November 20, 2024, 08:49:15 amI agree with you. That´s the most likely szenario since we don´t see laser tuned resistors or fuses.

author: iMo
author_rank: Super Contributor
timestamp: November 20, 2024, 02:29:24 pm
content: Quote from: daqq on November 20, 2024, 08:30:49 amOr, do wire a terminal to the pins and perhaps you get a splash screen asking for password, and after entering "REF80" you get "Enter the required output voltage [1.xxxxxxxx to 10.xxxxxxxx, or type "help"] > "

author: Kean
author_rank: Unknown
timestamp: November 21, 2024, 01:46:58 am
content: Quote from: iMo on November 20, 2024, 02:29:24 pmPDVS2mini on a chip. Yes please!

author: Noopy
author_rank: Super Contributor
timestamp: November 21, 2024, 07:12:06 pm
content: And now? Should we apply some HF?

author: floobydust
author_rank: Super Contributor
timestamp: November 21, 2024, 07:55:57 pm
content: Are their any FLASH or EEPROM memory cells on the die?I'd expect a copy and paste of some small MCU, compared to the high NRE costs of designing a state-machine from scratch.The correction functions (in the patent) are 2nd order parabolics for temperature and voltage, coefficients stored in a matrix. Third-order is also shown. So it's a bit of math.I can't see this corrector doing clunky switching of FET switches as a DAC- although step-changes with temperature were thought to be die stress creaks in Reply#63but I could be wrong.

author: Noopy
author_rank: Super Contributor
timestamp: November 21, 2024, 07:59:15 pm
content: There is a good chance of findt memory cells after removing the metal layers...

author: iMo
author_rank: Super Contributor
timestamp: November 21, 2024, 08:52:03 pm
content: Quote from: Noopy on November 21, 2024, 07:12:06 pmCould you apply the HF such you etch the layers extremely slowly step by step, making shots after each step?

author: Noopy
author_rank: Super Contributor
timestamp: November 21, 2024, 08:54:13 pm
content: I will try do take some pictures from time to time but the etching process is very uneven. Otherwise delayering would be easy...

author: iMo
author_rank: Super Contributor
timestamp: November 21, 2024, 09:03:16 pm
content: Let the owner of the chip decide.. GO/NOGO..

author: Noopy
author_rank: Super Contributor
timestamp: November 21, 2024, 09:06:27 pm
content: I have bought it, it's mine......but I'm very grateful dlebed sold it to me.

author: Noopy
author_rank: Super Contributor
timestamp: November 22, 2024, 04:07:09 am
content: Just to clarify what I can do and how I do it:I have HF (Armour Etch) and HCL. That should be good enough for silicon oxide and aluminum.Here you can see how I try to delayer a ADR1000 with its two metal layers:https://www.richis-lab.de/Howto_Decap_HF.htmEtching the upermost passivation layer is ok. While etching the second metal layer the first metal layer gets dissolved too. There are always openings through which the acid advances quite fast. And there are still silicon oxide "hills" standing around.Unfortunately under the first metal layer there is a layer which can´t be removed. It is either a barrier layer and/or a layer that optimizes the junction between silicon and metal.In the end I just can work with underetching the silicon oxide to remove everything, silicon oxide, metal, barrier, polysilicon,...The REF80 is much more complex so I don´t think it will be easier to remove one or two metal layers. But taking a look at the substrate can be very interesting like you can see here with the ATtiny10:

author: dlebed
author_rank: Regular Contributor
timestamp: November 30, 2024, 08:44:55 am
content: I finally got my GND measurement boards (with all GNDs routed separately). It took about two weeks as I've waiting for "After Dark" OSHPark's PCBs.Here is the summary of my measurementsI put small resistors between each power and ground node to measure current between them.NB: Current measurements might be affected by thermal EMF (shunt voltages were at most a couple mVs), so it's not ultra precise, but 100uA and 1mA are easily distinguishable.Looks like pin names are assigned more or less correctly.Findings:- There is almost no current that goes into GND pin (13), only about 100uA - this might be a digital ground, indeed- Pin 15 is main Zener ground, all 14mA goes through it and not through pin 14- Pin 14 seems to be GND sense, <100uA current flows there- Pin 4 is Zener + Force- Pin 5 is Zener + Sense (~130uA flows there when idle)When 1mA load is attached between pins 4 - 15 (proclaimed Force +/-), then current flowing into Pin 14 (GND_Sense) does not change at all, current into REFZ_Sense (5) drops by ~60uA.When 1mA load is attached between pins 5 - 14 (proclaimed Sense +/-), then current starts flowing from Force pins. Amount of external current is different: entire 1mA flows between GND sense/force, but only 0.72mA flows between REFZ sense/force.So we're probably looking at something like 10 Ohm resistance (3mV at 0.3mA) between REFZ sense (5) and force (4) pins.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 02, 2024, 10:13:58 am
content: It is a bit surprising to get 2 so different Ref GND pins. There is not much headroom at the low side for any amplifier or active circuit for the pins 14 and 15. Much of the imbalance could be from the 4.7 ohm resistor to measure the current.It is a bit surprising to see so little current to pin 13. I would have expected a little more, more like 1 mA for the amplifiers.

author: magic
author_rank: Super Contributor
timestamp: December 02, 2024, 10:33:54 am
content: Can the buffer sink current? What happens to GND and supply currents then?There seems to be no load regulation spec, not sure what to think about it.

author: iMo
author_rank: Super Contributor
timestamp: December 02, 2024, 01:35:19 pm
content: The output load capability could be checked easily by loading the output by 3-4 resistors while measuring the output voltage. The excel will show you the slope with the output resistance then (like the "1R7" in case of the first ADR1001 samples).PS: the load shall be lower than 1mA (DS), so for example load it w/ 330k, 100k, 33k, 10k..

author: Noopy
author_rank: Super Contributor
timestamp: December 02, 2024, 02:42:45 pm
content: I have some more information regarding the REF80:A look at the publicly advertised processes from Texas Instruments suggests that the HPA07 process was used in the REF80. (I´m not sure about that!) This process dates back to 2003 and is referred to as “High-Performance Analog CMOS”. The HP180, which is based on the AN180, would also be conceivable. It is described as “extremely low-noise, high precision”. However, the HPA07 is also available as HPA07HV, where it allows up to 36V. The HP180 only allows 24V. This makes the HPA07HV somewhat more likely. The maximum heater voltage of the REF80 is specified as 42V. In my view it is possible that the HPA07HV can handle the 42V with additional measures.The minimum structure width of the HPA07 is 0,3µm. Special isolation structures are available to shield sensitive circuit parts from potentially interfering circuit parts. MOSFETs, JFETs, NPN and PNP transistors can be integrated. The transistors have a very low noise level. The process offers metal-to-metal capacitors, IMD capacitors and titanium nitride polysilicon capacitors. In addition to polysilicon resistors, precision thin-film resistors can be used, which can also be tuned with a laser process. Polysilicon fuses and memory cells are available for configuration, including OTP EPROM and EEPROM. The top metal layer can be a particularly thick copper layer.In the following pictures, layers of the integrated circuit have been removed piece by piece. This is not a professional delayering. For this reason, the removal of the layers is inhomogeneous and some structures can only be removed by underetching. Nevertheless, new interesting insights are gained.Initial state:https://www.richis-lab.de/images/REF01/51x08XL.jpg(43MB)After 12min HF:https://www.richis-lab.de/images/REF01/51x26XL.jpg(42MB)After 5min HCL:https://www.richis-lab.de/images/REF01/51x27XL.jpg(45MB)After 12min HF:https://www.richis-lab.de/images/REF01/51x28XL.jpg(45MB)After 12min HF:https://www.richis-lab.de/images/REF01/51x29XL.jpg(47MB)After 12min HF:https://www.richis-lab.de/images/REF01/51x30XL.jpg(45MB)After 96min HF:https://www.richis-lab.de/images/REF01/51x31XL.jpg(47MB)Many areas are surrounded by relatively thick frames. These are most likely the special insulation structures offered by the HPA07 process. Some elements can be clearly assigned to CMOS and bipolar transistors. The structures that can be seen here have an unusual asymmetry. They probably form so-called DEMOS, Drain Extended MOS.In the book Silicon Analog Components by Badih El-Kareh and Lou N. Hutter, there is a comparison of DEMOS and LDMOS transistors. Lou Hutter was involved in the development of many processes at Texas Instruments.In the left-hand area, a logic structure was already expected due to the wiring in the top metal layer. This is confirmed at the substrate level (blue). Above and below the control logic are two very similar blocks (cyan). Two rows of resistors and two rows of transistors are integrated in each block. Judging by the optical appearance, this could be a kind of simple DAC.Under the four bondpads, which provide the reference voltage, there are some larger elements (yellow). Exactly the same elements can also be found under the four bondpads in the lower area. It therefore appears that this is actually a second output.A very large area in the lower section of the die is covered with capacitors. The capacitors were realized in the metal layers and have already disappeared here. Underneath are some kind of strips. These appear to be further capacitors.In addition to many smaller transistors, several larger transistor groups are integrated (red). The heater voltage is supplied in the top right-hand area and this is also where the output is located, which indicates when the set temperature has been reached. It is therefore not surprising that there are large transistors in this corner. Below the frame structure, which distributes the heater current, there are thin, long rows of transistors. It can be assumed that these transistors fulfill a task as part of the heating function. Outside this frame, four slightly larger blocks are arranged symmetrically. These could be the output stages for the reference voltage output. A certain amount of power loss is to be expected there, which is better distributed as symmetrically as possible. The smaller transistor strips inside the frame could be current sources for the four reference voltage sources.The double lines that are typical for logic circuits can now be seen on the substrate (yellow). Some of the polysilicon strips that represent the gate electrodes have remained. While the logic within the double lines has a chaotic inhomogeneity, repetitive structures stand out on the left (cyan). These are most probably memory cells containing correction values. It appears that the memory cells are located in the middle and are flanked on the right and left by circuit parts via which the cells can be selected, written to and read out.Here you can see the transistors and Z-diodes, which most likely supply the basic reference voltage. The many small elements that resemble dirt are the remains of the contacts between the layers. In more modern processes, these vias are lined with metals that do not dissolve and then remain as sleeves or cylinders.The area on the right now also shows what is under the large cross-shaped metal surface in the middle. These are relatively simple structures.In an intermediate step, it can be seen that a series of resistors were located in a higher layer. The resistors have surprisingly complex contacts and are embedded between the metal layers.With the information obtained, the following assumption can be made. The voltage for heating the REF80 is fed via the metal layer to a frame of transistors that regulate the heating power (yellow). From there, the current is conducted to resistors (red) that surround the four reference voltage sources (green). A great deal of effort was put into the design of the heater resistors, presumably to distribute the heat as homogeneously as possible and to prevent electrical interference. Temperature sensors (purple) close the control loop.https://www.richis-lab.de/REF46.htm#etch

author: iMo
author_rank: Super Contributor
timestamp: December 02, 2024, 03:40:32 pm
content: So.. do we need all this in order to generate 7V DC.. ?

author: Noopy
author_rank: Super Contributor
timestamp: December 02, 2024, 04:13:28 pm
content: It seems they tried to achieve a precision voltage reference by throwing everything they have onto a wafer.The usual way you build analog precision parts today.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 02, 2024, 04:19:25 pm
content: Chances are that some of the circuit is not used, especially the part connected to the 2nd output with the unused band pads / 2nd output.Having many units in parallel and average is a way to get symmetry and this way get less sensitive to temperature gradients across the chip.One a chip there is essentially no extra costs for 10 small transistors compared to 1 larger one with 10 x the area. It may even be easier as the small one are the more standard sizes for the process.The digital trim part also needs quite some transistors / memory cells, but should not use much area. Much could be known working blocks taken over from other designs (e.g. OP-amps or ADCs). So this looks complicated, but could be easy for the designers.The analog temperature regulation may need relatively large capacitance. The LTZ1000 uses quite large external capacitors in the temperature regulation. There can be a few ways to reduce it, but it still needs relatively large time constants.

author: iMo
author_rank: Super Contributor
timestamp: December 02, 2024, 04:44:21 pm
content: The REF81 will be with 2 outputs:OUT1 .. 7.6V Vref as it is todayOUT2 .. via 8/10 bit serial input configurable (simple serial bitbanging), say 0.5V -7.6V in 8 or 10bit resolution

author: dlebed
author_rank: Regular Contributor
timestamp: December 03, 2024, 07:07:47 am
content: QuoteI already did that before (see my previous posts in this thread), my initial design with suboptimal GND connection had about 0.8Ohm output impedance.Once I split GND I was able to see output impedance drop to about 0.4Ohm at 1mA load.

author: dlebed
author_rank: Regular Contributor
timestamp: December 03, 2024, 07:21:47 am
content: REF80 noiseWhile my LNA is under construction, I got an LNA from trtr6842 (thanks!), so now I was able to measure REF80's noise compared to .... US Cal Club's 10V FX Reference that happen to visit meLNAhttps://www.eevblog.com/forum/metrology/diy-0-1-to-10hz-noise-amplifier/What I can say, it performs up to spec and is actually better noise-wise than FX Reference.Here is the baseline noise from the LNA itself (inputs shorted).REF80 Noise40uF film capacitors on REF output, LTC3045 LDO as to filter out input supply noise, 15V supply voltage for heater/reference.US Cal Club FX ReferenceNo modifications done, warmed up for multiple days already.Summary:REF80has about 1.3uV p-p noise @ 7.6V (0.17ppm p-p) - datasheet states 0.16ppm p-p typ.FX LTZ1000has 3.09uV p-p noise @ 10V (0.3ppm p-p)

author: iMo
author_rank: Super Contributor
timestamp: December 03, 2024, 07:45:46 am
content: The LTZ FX noise (3.1uVpp @10V) looks rather high - at the 1399 level, imho..

author: Andreas
author_rank: Super Contributor
timestamp: December 03, 2024, 09:19:25 pm
content: Hmm,for me it looks like there is a oscillation within the signal (mains hum?)Can you do a FFT of the measured signals? (hope you have stored them).Why do you use 0.5sec/div in one of the measurements?(for measuring 0.1-10 Hz you need minimum 10 secs total aquisition time).I would also use minimum 1000 kpts total aquisition (for having a high resolution FFT).with best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: December 03, 2024, 09:31:49 pm
content: An FFT on the noise data would make sense. I see little need in using 1M points. If the sample length is fixed the extra points would only give extra points for higher frequencies and there is little use in these. It would make sense to use a time window well more than 10s for the FFT, as the low end tends to be noisy. Some randomness can be an issue anyway if there is popcorn noise with a relatively low transition rate, like with most LM399. So one would look at the pp noise over many 10 second windows and than average the pp values (one could argue about averaging as power).The FX ref. seems to have quite some popcorn noise with mulitple levels.

author: dlebed
author_rank: Regular Contributor
timestamp: December 03, 2024, 11:40:13 pm
content: FFT I originally attached was incorrectly labeled as REF80 while being an FX LTZ.I will recapture the FFT for both the FX and REF80 and post the results.I did that in peak hold mode to average aver time, I will pay more attention to settings this time.Maybe I will eventually just use DMM7510 as a digitizer + some python for it to get better results.

author: dlebed
author_rank: Regular Contributor
timestamp: December 04, 2024, 06:48:25 am
content: Andreas, I used 0.5sec/div only for quick inherent noise estimation for the LNA itself (with shorted inputs).As you can see the noise is an order of magnitude lower, so I did not spend much time capturing that.Doing longer capture won't really change the the overall picture.As Kleinstein mentioned, from time domain picture it's pretty clear that FX LTZ reference has quite a bit of higher frequency noise content, while REF80 is more smooth and does not have as much noise at higher frequencies.TBH I have not yet checked this particular FX reference box schematic to see where this noise could be coming from (amplifier? resistors?).I did a few longer FFT runs with the scope and the noise spectral density different is indeed there.REF80 FFT30 minutes averaging, p-p mean value (20 sec interval) over 30 minutes is 1.34uV for 7.6 VREF output (0.17ppm p-p), so no change from my previous shorter measurement.Absolute maximum noise span over 30 minutes is (0.9-(-0.9)) = 1.8uV, which is 0.23ppm p-p.FX LTZ100 FFT8 minute averaging, p-p mean value (20 sec interval) over 8 minutes is 3uV for 10V VREF output (0.3ppm p-p), is aligned with my previous data.Absolute maximum noise span over 8 minutes is (1.858-(-1.866)) = 3.7uV, which is 0.37ppm p-p.Noise SpectrumAs you can see, REF80 has a different noise spectrum in 0.1-10Hz range with a clear peak (~ -148dBV) at around 0.1-0.2Hz region and average noise level of ~ -159dbV in 0.5-10Hz region.FX LTX reference on the other hand has pretty much flat noise spectrum plot in 0.1-10Hz range with a level of ~ -148dBV.

author: iMo
author_rank: Super Contributor
timestamp: December 04, 2024, 07:42:14 am
content: When comparing with the ADR1001 - here is the noise in 0.1-10Hz I measured with my simple noise tester -> 1.6-2.3uVpp @10V in 10 independent 12secs long measurements, its 10V output buffered by the OPA189..https://www.eevblog.com/forum/metrology/adr1001-ovenized-voltage-reference-system/msg5154198/#msg5154198

author: dlebed
author_rank: Regular Contributor
timestamp: December 04, 2024, 08:30:35 am
content: Here isLM399result measured with the same setup for the sake of completeness.Buffered 7V output (ADA4523-1) over 12 minutes gave mean 3.68uV p-p over 20 second interval, resulting in 0.52ppm p-p and 7.2uV absolute span (~1ppm p-p).Nothing special, well known popcorn noise is present.Y axis scale is different from the plots above.

author: Andreas
author_rank: Super Contributor
timestamp: December 04, 2024, 08:06:27 pm
content: Hmm,but how is the behaviour near the mains frequency?A transformer within 50 cm can create a significant peak even outside the bandpass filter frequency.with best regardsAndreas

author: dlebed
author_rank: Regular Contributor
timestamp: December 05, 2024, 06:08:12 am
content: Andreas,Here is behavior including mains frequency (60Hz).LF LNA with shorted inputsThere is 54.5Hz small peak there, this seem to be something inherent to the setup.REF80FX LTZ1000REF80's Power SupplyREF80 and LTZ references are powered by different power supplies, both are linear.REF80 power comes from a custom built DIY PSU based on LT3081, its noise is aligned with LT3081's datasheet (27uV RMS), it's based on low-leakage shielded transformer.There are also a few CLC filters in REF80's power supply chain.All captures made with the same setup.NB: FX's noise p-p level dropped from ~3uV p-p yesterday to ~2.1uV p-p today, I did not change anything and REF80's noise remained the same.

author: floobydust
author_rank: Super Contributor
timestamp: December 05, 2024, 07:20:13 am
content: Don't forget to examine for mains 2nd harmonic at 100/120Hz when using full-wave bridge rectification.I'll use a simple signal tracer, an audio amplifier out of a LM386 $2 on Ali/eBay and listen to the noise.You might hear hum, powerline hash, cell-phone/WiFi/cordless phone RF TX chirps, microphonics, LED/fluorescent lighting, AM radio, oscillations etc.Saves a lot of time and you can also get a better idea of a lab's noise sources.

author: Andreas
author_rank: Super Contributor
timestamp: December 05, 2024, 08:11:57 am
content: Quote from: dlebed on December 05, 2024, 06:08:12 amWith magnetic stray from transformers small changes in distance can have a large influence.With each new measurement series I do a noise floor measurement and a check for mains frequency.with best regardsAndreas

author: laichh
author_rank: Regular Contributor
timestamp: April 09, 2025, 02:41:11 am
content: TI revised the datasheet from preliminary to production release in Mar-2025.https://www.ti.com/lit/ds/symlink/ref80.pdfThe 0.1 to 10 Hz noise is now 0.12 ppm(pk-pk), which is 0.9 uVpp typical.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: April 09, 2025, 03:40:49 pm
content: Quote from: laichh on April 09, 2025, 02:41:11 amMouser and Texas only sells those by batch/roll of 250 units...

author: nwind
author_rank: Regular Contributor
timestamp: June 02, 2025, 02:21:45 am
content: Did anyone figure out the way to get REF80 without buying 250pcs?

author: Rubo
author_rank: Regular Contributor
timestamp: June 02, 2025, 02:50:49 pm
content: You can buy the evaluation module REF8EVM for $199 directly from TI.https://www.ti.com/tool/REF8EVMor from DigiKey for $238.80https://www.digikey.com/en/products/detail/texas-instruments/ref8evm/26436292Looks like the have 2 in-stock.I've been thinking about getting one, since the actual chips aren't available yet.

author: iMo
author_rank: Super Contributor
timestamp: June 02, 2025, 03:00:18 pm
content: ..or somebody may organize a group buy..Btw., what is the idea behind the selling 250 quantities only?Perhaps they have got the chips in containers for 250 chips (like 10x25) only and nobody wants to mess with packaging single quantities? Lack of skilled resources perhaps??

author: Kleinstein
author_rank: Super Contributor
timestamp: June 02, 2025, 03:11:46 pm
content: It is kind of normal that Ti only sell full containers - so like the 250 pieces. It would normally be the job of distributors like Digikey / Mouser to take one and split them up. Even there it is a big sum and a rather special chip with possibly not that much demand.The chip still has a case that is not that convenient and the heater needs quite some power. The noise specs are not that great for the power and costs. On the upside the long term drift claims are quite good, but this still needs to be proven with a few more designs and batches.I still have some hope that Ti may offer smaller quantity orders to get things started.

author: iMo
author_rank: Super Contributor
timestamp: June 02, 2025, 03:29:17 pm
content: Quote from: Kleinstein on June 02, 2025, 03:11:46 pmSure, the greediness of the distributors caused they have no personnel for actual work left anymore, thus they just move the entire containers/boxes/tapes/rails, it seems..

author: nwind
author_rank: Regular Contributor
timestamp: June 09, 2025, 12:57:00 pm
content: I've got dev board from TI and in first ~15hrs it lost ~20ppm at 85C (soldered 805K as R2).Isn't it too much?There are some jumps in plot as well.My setup is kind of horrible since I was eager to power it up and start aging process, but ...TI dev board and documentation desired to be better as well especially for power connection.ADI did a better job for ADR1001

author: nwind
author_rank: Regular Contributor
timestamp: June 09, 2025, 12:58:59 pm
content: I'll post some graphs later.

author: TUMEMBER
author_rank: Regular Contributor
timestamp: June 09, 2025, 03:15:49 pm
content: Quote from: Kleinstein on June 02, 2025, 03:11:46 pmNot really related to metrology but to the specifics of the situation.Even DigiKey is some uncomfortable pimple on the ass for TI. The quantities they are able to order "don't pay off". This is production aimed at the "automotive" market, where the order batch for the "control module" project will amount to about a million or more. They want to sell not to a single supplier but to the entire corporate group, Volvo or VW alone does not count, but an association of a dozen or so brands "enters the game". It is exactly like with the household appliance market (dishwashers, refrigerators, washing machines and all that crap). Recently, the Whirpool brand disappeared in Poland, because it was "absorbed" by the Beko brand - the same in all the guts of these devices, but the "decor" is different, so a different brand. It is better to buy a batch of 10 million guts than 100 thousand - the unit cost is lower, and the profit from the sale of the final product is higher.

author: nwind
author_rank: Regular Contributor
timestamp: June 09, 2025, 03:53:13 pm
content: Quote from: nwind on June 09, 2025, 12:58:59 pm

author: Noopy
author_rank: Super Contributor
timestamp: June 09, 2025, 04:07:02 pm
content: Quote from: TUMEMBER on June 09, 2025, 03:15:49 pmIn principle I agree with you but here the situation is somewhat special. The automotive industry doesn´t need a ultra stable reference like the REF80. In my view the niche for such references is quite small. Quite often the references of the usual microcontrollers are good enough. If not there are cheap references which are good enough for most of the other circuits. As soon as you need a REF80 you also have to put quite some effort (and money) in the rest of the circuit too. Of course there are applications for the REF80 but I assume that they won´t sell huge batches every year.With that in mind smaller quantities could be interesting and a good promotion since companies can easily buy 10 or 20 to build and test a circuit that will later perhaps become a product. On the other hand getting samples is usually no problem especially when you can tell them about a possible product.

author: Andreas
author_rank: Super Contributor
timestamp: June 10, 2025, 08:41:13 am
content: Quote from: nwind on June 09, 2025, 12:57:00 pmDepends: (on some LM399 I saw several ppms drift within first week of operation).The question is: does it stabilize?initial drift may be influenced by many things:- soldering shift from production (now equalizing)- humidity equalisation between epoxy PCB and new environment. (creating stress to the chip).- reaction between chip and bonding material (which might not be finally cured).- ....And maybe also warm up or humidity equalizing drift by your instruments (they should be fired up minimum 1 week before use to settle).Unfortunately the time scale on both instruments is different so they cannot be compared.Are the "jumps" synchronous on both instruments or are they related to one of the instruments?with best regardsAndreas

author: nwind
author_rank: Regular Contributor
timestamp: June 10, 2025, 06:36:13 pm
content: Andreas,Jumps are too high and erratic and REF80 isn't LM399.There is something wrong with the setup or this particular dev board.Instruments are running non stop for days and I never seen with them anything like this with ADR1001 or ADR1399 boards.

author: nwind
author_rank: Regular Contributor
timestamp: June 10, 2025, 09:23:37 pm
content: As an example exactly same setup in the same location and similar ambient conditions with ADI ADR1001 dev board.4uVp-p not 80 and pretty much very stable.34465A is much more drifty with ambient temp changes than Hioki.

author: Andreas
author_rank: Super Contributor
timestamp: June 13, 2025, 07:58:00 am
content: Quote from: nwind on June 10, 2025, 06:36:13 pmHello,what I see in the zooomed part of the picture is ~15 uV Jump = 2 ppm.This is not unusual for a (bad) buried zener (popcorn noise due to impurities of the silicon).But you are right: for use in an instrument as reference I would discard this device.(select for < 0.5 ppm popcorn noise so skip every 2nd device see attached example for AD587)The question is where it comes from: The reference chip itself or from a defective output capacitor (cracks).What happens when you apply some (dosed) force to the pcb (slightly bending).with best regardsAndreas

author: rsjsouza
author_rank: Super Contributor
timestamp: August 12, 2025, 07:15:12 pm
content: Quote from: nwind on June 02, 2025, 02:21:45 amJust add one part to the cart?

author: Rubo
author_rank: Regular Contributor
timestamp: August 12, 2025, 09:40:06 pm
content: Quote from: rsjsouza on August 12, 2025, 07:15:12 pmFrom where? Are they in stock now?I'm going to answer my own question. Yes, they are available on TI websiteP.S. Order placed

author: Noopy
author_rank: Super Contributor
timestamp: August 17, 2025, 07:23:13 pm
content: Not for us in the EU?

author: Hydron
author_rank: Super Contributor
timestamp: August 17, 2025, 11:05:15 pm
content: I looked on Friday and no stock at TI, annoying as I was placing another order anyway

author: Rubo
author_rank: Regular Contributor
timestamp: August 21, 2025, 01:30:19 am
content: Well... It's here...Now I need to figure out a way to test it while avoiding soldering to it (it will be a last resort).I was thinking of finding some thing like this:https://www.mouser.com/ProductDetail/Yamaichi-Electronics/NP404-02412-1?qs=j1jvDfvplqKXtnpSrNW9%2FA%3D%3DIf anyone has any suggestions I would appreciate them greatly.Sorry for the shit picture, have been having issues with my phone.

author: tszaboo
author_rank: Super Contributor
timestamp: September 15, 2025, 02:19:30 pm
content: Quote from: nwind on June 09, 2025, 12:57:00 pmWell technically it's within specification, since specification is N/A.If you ask me, it should be close to 3ppm. Unless they did some creative accounting, and 3ppm is done with calculation like this:"some had +100PPM drift, some -97PPM so we wrote +3 typical, which is statistically correct"I also don't like figure 6-1 where instead of plotting 20 different devices, they just went with an average.BTW, did you guys see the new release? REF81

author: iMo
author_rank: Super Contributor
timestamp: September 15, 2025, 03:30:40 pm
content: Yep, the REF81 is the competitor to the ADR1001.. (I wrote somewhere we have to wait a bit..)..PS: btw., they made the same mistake as ADI did with the output resistor divider - wired internally to the output of the buffer..

author: Simmed
author_rank: Frequent Contributor
timestamp: September 15, 2025, 03:43:29 pm
content: Quote from: tszaboo on September 15, 2025, 02:19:30 pmohcould it be that there is REF82 ?

author: Jacques
author_rank: Contributor
timestamp: September 17, 2025, 03:54:47 pm
content: Quote from: tszaboo on September 15, 2025, 02:19:30 pmThat is oneanemic datasheet, even for a preview part. It's a pity the minimum temperature setpoint is so high with these new temperature-regulated ADI and TI references. (I doubt they'll outperform an LM399 with a high-quality resistor network in practice.)

author: iMo
author_rank: Super Contributor
timestamp: September 17, 2025, 04:58:42 pm
content: REF81 will do 85/95/105/115C (provided it has got the same heater settings as the REF80 one), the ADR1001 can do from aprox 40C..120C (set by a resistor)..Quote from: Jacques on September 17, 2025, 03:54:47 pm

author: Jacques
author_rank: Contributor
timestamp: September 17, 2025, 07:36:45 pm
content: Quote from: iMo on September 17, 2025, 04:58:42 pmYeah -- I assumed the REF81 will allow for the same discrete temperature setpoints as the REF80. For the ADR1001, it's a substantially wider range than I (mis)remembered.