LM399 - die analysis - Page 1
Forum section: electronics / projects

author: Noopy
author_rank: Super Contributor
timestamp: January 17, 2020, 09:57:59 pm
content: Hi all,I have took a closer look on a LM399 shunt reference.Actually it´s a HP-part...You can find the whole story here:https://www.richis-lab.de/REF02.htm(german)A nice die with big structures!Reverse engineering is not a big deal:And here is the buried zener:I found a circuit that´s not in the datasheet:It seems they had to do some fancy compensation.And here the heater-circuit:I wrote a lot about the circuit but it´s too late to translate all that words to english. Please use the google translator and ask me whatever you want.BTW:I also have a PMI REF01:https://www.richis-lab.de/REF01.htmInteresting point: The new ones are ADR01 named REF01.Have fun!…does anybody want to donate me a (dead) LTZ1000?Update: Hey, it seem´s that I´ll get one out of the german mikrocontroller.net-Forum!

author: iMo
author_rank: Super Contributor
timestamp: January 17, 2020, 11:43:52 pm
content: QuoteYes, the Dobkin's paper confirms that.2 burried zeners there.PS: I can send you a MAC199 (TESLA's highest grade LM399 clone) for de-capping if interested.PPS: TESLA's schematics show the missing transistor and resistors, there is even one additional transistor more

author: rhb
author_rank: Super Contributor
timestamp: January 18, 2020, 12:02:22 am
content: What is a 1991 die doing in a 1985 date code package? Where did the device come from?

author: Squiddaddy
author_rank: Regular Contributor
timestamp: January 18, 2020, 12:55:26 am
content: Looks like 199 I to me, not 1991.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: January 18, 2020, 06:22:00 am
content: Quote from: rhb on January 18, 2020, 12:02:22 amThe original part was LM 199

author: Noopy
author_rank: Super Contributor
timestamp: January 18, 2020, 06:43:22 am
content: Quote from: imo on January 17, 2020, 11:43:52 pmA MAC199 would be very interesting! I´ll write you a PN.And thanks for the hint to the schematic of the MAC199 and now I see the Double-Transistor. Will correct that on my homepage!And regarding the "datecode-problem":Thanks for the hint. Didn´t realize that!

author: Gyro
author_rank: Super Contributor
timestamp: January 18, 2020, 10:01:06 am
content: You can find die photos of the MAC199 in this thread:https://www.eevblog.com/forum/metrology/tesla-mac199mae299mab399-and-mac01-teardown-and-tests/

author: Noopy
author_rank: Super Contributor
timestamp: January 18, 2020, 12:10:50 pm
content: Quote from: imo on January 17, 2020, 11:43:52 pmI´m not sure whether that´s really a transistor:The bigger thing above the resistor-lines.In my view that is still a resistor.Well I´m not sure but I see nothing that indicates a transistor.Otherwise it would interact with the other resistors placed in the same well.I´ll try to take a better shot of the area…

author: Cerebus
author_rank: Super Contributor
timestamp: January 18, 2020, 01:40:16 pm
content: To save scrabbling about, here is the die photo of the Tesla chip (a MAB399) from the thread mentioned above:Note that the image links to a higher resolution version of the same image; so click on it if you want more detail.

author: Noopy
author_rank: Super Contributor
timestamp: January 18, 2020, 02:55:54 pm
content: It´s high resolution but not as high as I am able to get it.It seems to have some different structures but without polarised light it´s difficult to clear that up.

author: Noopy
author_rank: Super Contributor
timestamp: January 18, 2020, 05:00:02 pm
content: Quote from: Noopy on January 18, 2020, 12:10:50 pmNo, I don´t think that´s a Transistor...

author: Wimberleytech
author_rank: Super Contributor
timestamp: January 18, 2020, 09:05:28 pm
content: Quote from: Noopy on January 18, 2020, 05:00:02 pmLooks like a resistor to me

author: Noopy
author_rank: Super Contributor
timestamp: January 30, 2020, 10:33:41 pm
content: Hi all!Thanks to imo I was able to take some pictures of a MAC199:https://www.richis-lab.de/REF02a.htmThe structures are very similar but not exactly the same.Tesla had to do quite some mask revisions.In my view like in the LM399 there is no second additional transistor as described in the tesla datasheet.The schematic looks like this:The grey line is disconnected in the MAC199. So whatever the lower transistor compensated it´s not functional in the MAC199.Another interesting point is the die attach. The die is not directly bonded to the package. It sits on top of something which looks like a thinner die:...the LM399 has the same "double-die"...

author: Cerebus
author_rank: Super Contributor
timestamp: January 30, 2020, 10:50:40 pm
content: I can't find anything specific to the LM199/299/399 but it's not uncommon for voltage reference chips to have unconventional die attachments. Differential temperature related movement of the case and die, owing to the different temperate coefficients of expansion of the disparate materials, induces varying strains in the substrate causing drift. So some kind of 'floating' or compliant attachment makes sense for high precision references.

author: Noopy
author_rank: Super Contributor
timestamp: February 07, 2020, 08:33:39 pm
content: Do you remember me saying that in the LM399 there is a additional circuit similar that shown in the datasheet of the MAC199?I claimed one of the two additional transistors isn´t actually there. I was pretty sure that it´s a resistor:Well some days later: It could be a transistor!Probably the brown "resistors" are p-doped. If there is an additional n-doped area under the upper contact than we have a pn-structure. With the n-doped well you get an npn-transistor.Fine!If you don´t want that every structure in the well interacts with the half transistor the well has to be more positive than everything else. The most positive potential is the red one coming from left into the picture. But it seem´s that the well is connected to the second yellow contact of the resistor. Since the role of the transistor is a shorting of the resistor it´s ok to connect the well to the second highest potential, the second contact of the resistor.Fine!It´s more a parasitic transistor and possibly not a very good one but it should work.

author: David Hess
author_rank: Super Contributor
timestamp: February 09, 2020, 12:39:07 am
content: Quote from: Noopy on January 30, 2020, 10:33:41 pmI suspect that was added for strain relief. All precision analog ICs have extra packaging requirements to prevent straining the semiconductor die.I remember an interview where I think it was Bob Dobkin who mentioned a National executive who kept complaining about the extra packaging cost of analog ICs and why couldn't they use the less expensive digital IC packaging which lacked an extra encapsulation which lowered strain. Then later someone actually ordered that change and suddenly all of their linear ICs were failing testing and they had nothing to sell.Quote from: Noopy on January 17, 2020, 09:57:59 pmSchematics often leave out circuits for things like transconductance reduction like common LM324 and LM358 schematics do.

author: Noopy
author_rank: Super Contributor
timestamp: February 09, 2020, 01:26:40 pm
content: Quote from: David Hess on February 09, 2020, 12:39:07 amOften heard about this.It´s interesting that the "better" LTZ1000 doesn´t have a "double-die":Richis-Lab - LTZ1000

author: Cerebus
author_rank: Super Contributor
timestamp: February 09, 2020, 02:18:24 pm
content: Quote from: Noopy on February 09, 2020, 01:26:40 pmThe LTZ1000A has its own proprietary die attach. This differs from the non-A version, the A version being engineered for lower thermal conductivity. It's mentioned on the first page of the data sheet.

author: Noopy
author_rank: Super Contributor
timestamp: February 09, 2020, 02:24:34 pm
content: Quote from: Cerebus on February 09, 2020, 02:18:24 pmI know the LTZ1000A has a special die attach but the datasheet descripes only special thermal properties.Of course it´s possible that it has additional special features...