The TLV760xx regulators are a nice piece [s]of crap[/s] - Page 1
Forum section: electronics / projects

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 09, 2019, 03:33:42 am
content: Hi all,I just want to say that these regulators are crap. TI already has a complain of a TLV76033 regulator blowing up ant taking other devices with it. I can confirm that I had 5 TLV76050 regulators blowing up and damaging other ICs, even at a very low load, and normally at powerup. Really, don't use them.Anyways, TI assumes all is fine and doesn't give a cent. I'm better off using the TPS70950 instead.Kind regards, Samuel Lourenço

author: djnz
author_rank: Regular Contributor
timestamp: February 09, 2019, 05:32:02 am
content: Just out of curiosity, where were these parts sourced from?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 09, 2019, 10:12:27 am
content: Just out of curiosity, did you scope the input voltage and current to verify that they were within ratings at all times?Tim

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 09, 2019, 12:36:59 pm
content: Hi Tim,The parts were bought from Mouser. All the regulators were supplied with 24V and supplied no more than 16mA (to an expensive AD5551 and a LED).Kind regards, Samuel Lourenço

author: floobydust
author_rank: Super Contributor
timestamp: February 09, 2019, 10:31:57 pm
content: I'm not convinced the IC is a lemon. Although TI is still full of datasheet bullshit "... spikes up to 30 V — for example, appliances and automation applications."Anyone knows this part is a basic LDO in a SOT-23.The IC cannot withstand -ve voltage transients at all.35V max. input which at your 24V leaves little room for overvoltage transients.It's well known the +ve voltage spike from connecting a wall-wart or laptop adapter to a board can kill an LDO. It depends on the input capacitor and wiring inductance.TLV760uses Sziklai and TPS709 uses mosfet.Let us know if the TPS709 fixes your problem, but seeing the rest of your circuit would help before blaming the IC. It must have made alot of smoke.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 09, 2019, 10:34:58 pm
content: Ok, so no.Take those measurements, and there you will find your answers.Tim

author: aheid
author_rank: Regular Contributor
timestamp: February 09, 2019, 10:44:19 pm
content: Probably unrelated, but I got curious. Junction to ambient is listed as 270 C/W, with 16mA @ 3.3V out with 24V in, that'll be about 90 C above ambient, no? Without additional cooling, is this a bit marginal or ok?

author: floobydust
author_rank: Super Contributor
timestamp: February 09, 2019, 10:59:11 pm
content: The little SOT-23 is on a PC board so I would estimate using RθJB Junction-to-board thermal resistance 56.8°C/W16mA out is about 0.33W or 44°C, assuming there is some copper for heatsinking.24V input is high for a 3.3V LDO, high stress on power up charging output capacitors. Output short-circuit current graphs datasheet fig. 11, 12 look pretty awful.It's going to pop.

author: tszaboo
author_rank: Super Contributor
timestamp: February 09, 2019, 11:13:34 pm
content: Just drop in a 470 Ohm resistor on series with the input pin.But why would you not drive the LED directly from the 24V in the first place?

author: aheid
author_rank: Regular Contributor
timestamp: February 09, 2019, 11:25:47 pm
content: Quote from: NANDBlog on February 09, 2019, 11:13:34 pmNot just a LED.Quote from: bloguetronica on February 09, 2019, 12:36:59 pm

author: aheid
author_rank: Regular Contributor
timestamp: February 09, 2019, 11:27:15 pm
content: Quote from: floobydust on February 09, 2019, 10:59:11 pmAh, misunderstood then, thought junction to ambient was via all paths (so board included). Thanks!

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 10, 2019, 02:54:09 am
content: Quote from: floobydust on February 09, 2019, 10:31:57 pmSo, I should know that this part is garbage, then?Quote from: floobydust on February 09, 2019, 10:31:57 pmWho mentioned something about negative supplies here?Quote from: floobydust on February 09, 2019, 10:31:57 pmNot an argument I'm willing to accept. My linear and regulated power supply doesn't make excursions to 35V out of a sudden. 24V for a 35V absolute maximum shows that there is plenty of headroom. I'll soon test the TLV76033 and the TLV76050 on two spare boards, without no downstream components, except a 10uF capacitor and a resistor to drain 16mA. Then, after these regulators are blown (hopefully and most certainly they will), I'll use the TPS70933 and the TPS70955 in their place (provided that I can use some pads and wires for that).As for the rest of the circuit, there was a chance that the INA180 could source some current to the 5V rail, but I confirmed that not to be the case. I took out other components that are in contact with other voltages from the 5V rail, and that still happens.Quote from: T3sl4co1l on February 09, 2019, 10:34:58 pmSee the attachments. Only a short circuit on the supply can cause spikes up to 35V, but that is rare.On the other hand, I've used regulators rated for 16Vbeing fed by 9V DC-DC supplies, and had no problems. The headroom in that case is far smaller and the spikes can surpass 16V easily. But, again, I'm talking about extreme events like short circuits on the supply rails, upstream from the regulator. That is not what happened. I didn't have massive capacitors in my circuit the last times this happened. Anyways, even in that case, the 1uF capacitor that I've used should absorb the spike.Quote from: floobydust on February 09, 2019, 10:59:11 pmYes, 16mA@24V is a bit extreme, but still tolerable. This LDO is advertised for 30V operation, but weak in practice. The SC protection doesn't work as advertised.Quote from: NANDBlog on February 09, 2019, 11:13:34 pmIf you need to do that, then you know you have a crappy regulator. Anyway, a resistor set as described won't save your regulator in a no-load condition. It is best to use a better, more robust regulator.Kind regards, Samuel Lourenço

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 10, 2019, 03:56:48 am
content: Quote from: bloguetronica on February 10, 2019, 02:54:09 amIt's a good caution in case of transients. Stuff come out of nowhere. Surge can be induced from nearby sources (most often, very fast pulses like ESD and EFT), from hot-plugging and accidental shorting, or from the load, or through other equipment connected to the device in question.Never hurts to be paranoid. Not having seen it, just means you haven't probed it in the right place when it happens.QuoteActually, 48V is the expected worst-case for hot plugging; potentially several times more if ceramic caps are involved!QuoteI see positive clipping at ~16V, and the measurement says "19?" because it knows it's clipping (evidently the clipping happens somewhere offscreen). Was the ultimate peak actually 35V?1uF is actually a risk factor, not a helper in this case!We can apply AC transient theory, with a few judicious guesses, and figure out what's happening.Suppose the source is a "9V" wall wart*, say 2m cable, OCV = 12V, nominal load 500mA (so, it's internally probably something like, an impedance-protected transformer, bridge, and 1000uF filter cap with << 1 ohm ESR). The cable is probably small zip cord, which will be around 0.3uH/m, or 0.6uH total.When this is hot-plugged to the EUT, the voltage at the end of the cord is shorted to ~zero by the input filter cap. This draws a rising current through the cable's ESL. The initial rate is dI/dt = V/L, or about (12V) / (0.6uH) = 20 A/us. If the capacitor is 1uF (nominal) and very low ESR (a ceramic would have maybe 0.1 ohm at this effective frequency), it forms a resonant circuit with the cable, so the current rises and, as the current rises, the voltage also rises. If there is no ESR in this circuit, then the resonance will continue to its full peak.Some time later (after 1/4 wave), the voltage is nominal (say 9 to 12V) but the current is maximum, so the voltage keeps going further. By 1/2 wave, it stops at a peak of up to 24V (or, again, more if this is a nonlinear ceramic). Now the output voltage is higher than the source, and current is ramping backwards, and the same thing happens again in reverse.What time scale is this wave? The resonant frequency is:Fo = 1 / (2*pi*sqrt(L*C))or 0.2MHz. The period is 1/Fo, and we can divide that period into whatever fractions of the wave we like. So, 5us total, or 1.25us to reach nominal voltage, 2.5us to reach peak, and so on.What if we include ESR?The source, cable, and input filter cap ESRs are all that matter so far. Any additional load there might be, should also be included, but the LDO for example acts in parallel, so we need to use a parallel-series conversion for that, which may not be representative in the conditions we're considering anyway (in which case, we might as well hand-wave it, or simulate it).The LDO also has a constant-current input characteristic, meaning it doesn't affect the AC waveform most of the time. We can ignore it for now.Now, ESR is generally undesirable for a power supply, right? The purpose of a supply is to deliver a stable voltage, and the definition of resistance is a change in voltage with a change in current! Well, the reality of it is this: nothing can be actually-zero ohms (except superconductors at DC, but there isn't really such a thing as true DC, either, hmm!), so we need to look for how much impedance we can actually handle, and meet or exceed that spec.Of course, an LDO's purpose is to stabilize a potentially messy source, so we shouldn't need to be very picky about it in this case! We don't know what impedance is required, but we do know that a mostly-capacitive impedance (i.e., the suggested 1uF) will do, so we can match that, more or less. (In particular, that impedance will only be critical around the crossover frequency of the LDO's control loop -- this isn't a tip you'll ever see in a textbook or app note, but that's what they're actually doing it for.)So, that said, we can add ESR to the 1uF until we have a well damped resonant circuit. How do we figure that out? Well, it comes down to the solution of a quadratic equation. If the solutions are complex, it resonates; real, it dampens. This happens to cross over at what we call the characteristic impedance:Zo = sqrt(L/C)If ESR > Zo, it's dampened, else, resonant.sqrt(0.6uH/1uF) ~= 0.8 ohms, so we don't need much. And really, relative to a 16mA load? That's going to be more than fine. We could get away with tens of ohms and still have a happy regulator, I would bet.We can connect a resistor in series with the cap, or we can simply choose an electrolytic with around that much ESR. (Tantalum is handy for its built-in ESR -- and is much more stable than electrolytics' ESR -- but is not recommended for heavy supply rails and inrush, so we won't use them here.)And we're done, right?Well, we might take an extra moment to check worst-case conditions. Maybe we need a lower impedance at the regulator anyway (this would definitely be the case for an SMPS regulator!). Maybe we need to support longer cables, or softer supplies. In that case, we might need a bare capacitor in parallel (without much ESR). We can effectively slow it down, by connecting an R+C in parallel with it, where C >= 2.5 Co and R = ESR.To handle longer cables (more ESL), Zo goes up, which means required ESR goes up even more. To counter this, we can grow C proportionally. This also gives us access to smaller ESRs in electrolytic type.In short, don't worry too much about a relatively large cap -- as long as it's got enough ESR. 'Lytics are great for this; you can usually pop in, say, 100uF and not worry about it.*I didn't notice if you mentioned what the typical source is, so I'm using an example here. This isn't a straw-man by any means; drop in the appropriate parameters for another source and see what happens. For example, a 9V battery on a 150mm clip lead, I would expect to see ESR in the several-ohms range, and ESL around 100nH. With Zo = sqrt(0.1uH/1uF) ~= 0.3 ohm, the battery ESR will dominate, and the circuit will just kind of gothudwhen turned on.Tim

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 10, 2019, 04:52:21 am
content: Well, I did more tests. Managed to kill a TLV76050 by shorting the supply upstream several times (killed by a spike, certainly). Tested a TLV76033 in the same way, but it held. Next I've shorted the output and bang, killed it. Tested a second TLV76050 by shorting the output at progressively higher voltages, and noticed the SC protection fails at 19V. Didn't killed any by unplugging and re-plugging the supply.In the case of the TLV70933, the load was a 100nF and a 2.2uF ceramic, a 10uF tantalum, and a 220resistor. In the case of the TLV70950, I've used a 330resistor in place of the 220one, being the caps the same.I can only speculate that the regulator got damaged by a residual current originated by the OPA2180, via the AD5551. The OPA2180 was supplied directly by 24V, while the AD5551 was supplied by the 5V from the regulator. The output of the AD was connected to the input of the OPA. As far as I know, the inputs of an OPAMP can't inject the current back into the circuit, but I might be mistaken.I'll test the TPS70933 and TPS70950 in a latter day. In my case, even if they don't resist the spikes, they will probably be more robust than the TLV760xx, since they can manage some voltage at the output while having no voltage at the input. They have reverse current protection, unlike the TLV760 series.Kind regards, Samuel Lourenço

author: floobydust
author_rank: Super Contributor
timestamp: February 10, 2019, 04:59:17 am
content: 250mA and 500msec/div

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 10, 2019, 05:07:06 am
content: Quote from: floobydust on February 10, 2019, 04:59:17 amUnfortunately, they haven't made a plot representing the capacity of this regulator to output the input voltage when failing. This regulator family is expunged from my current and future designs. I ven deleted the Eagle libraries that I had created previously. It would be a crime not to do so.Kind regards, Samuel Lourenço

author: tszaboo
author_rank: Super Contributor
timestamp: February 10, 2019, 09:23:46 am
content: Quote from: bloguetronica on February 10, 2019, 02:54:09 amA) You are clearly overloading the regulator. "Continuously running the TLV760 into thermalprotection degrades device reliability."B) Yes, it will save it, because it will dissipate the heat instead the TINY LDO that you are using with higher loads, provide short circuit protection, and reduce the turn on transient.C) If shorting the regulator output blows it up... Then dont short it?! Why is this even discussed? It is not standard operation to short the output, a SOT23 LDO is not a CC CV power supply.

author: iMo
author_rank: Super Contributor
timestamp: February 10, 2019, 12:12:39 pm
content: The TIs datasheet calculates (8.1.3) the max power with RThJA=275degC/W, however.With 24V input, and 3.3V/16mA output it gives you 91degC above ambient.When the output is shorted the current could be 60mA (see the Fig.12 for 10V input), thus close to 400degC above ambient..

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 10, 2019, 01:44:49 pm
content: Quote from: NANDBlog on February 10, 2019, 09:23:46 amA - It is possible.B - No it doesn't protect the LDO from surges which, in any case, didn't happened when the AD5551s got fried.C - This was done to assess the reliability of the regulator.Quote from: imo on February 10, 2019, 12:12:39 pmSince the regulator is not floating in mid-air, you should use the junction to board figure of 56.8ºC. You then have 0.3312W of dissipated head, giving you a rise of 18.84ºC above ambient.Anyway, the schematic is attached (the TLV76050 was replaced by the TPS70955, and the respective capacitors as well). You can see that there is no reason why this board failed on power-up.Kind regards, Samuel Lourenço

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 10, 2019, 02:57:05 pm
content: Well, it seems that the TPS70933 is even worse. It requires a 1K resistor in series with the input. Direct to 24V it blows instantly. Ok, back to the TLV760. I wonder if a choke could absorb those spikes. Or perhaps a 220resistor.Kind regards, Samuel Lourenço

author: Warhawk
author_rank: Frequent Contributor
timestamp: February 10, 2019, 04:25:30 pm
content: Look, I don't know what you're exactly doing but I recommend posting this on the E2E forum which is available online and is free of charge. Somebody will start dealing with your issue typically in less than 24 hours. It would be great if you could post pictures of your setup and eventually a circuit diagram. This often helps. (huh, how many times we've seen customers complaining that TI produces shit and then we saw a 2 MHz switcher without a PCB, put together with just a bunch of jumpwires...).It may be a quality issue but I've been using e.g. TPS70933 for some time (last time today!) and have not had a problem yet.PS: Not only TI has a lot of bullshit floating around. It is simply difficult to get qualified staff and customers want LDOs for 1 cent.Best Regards,Jiri, TI

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 10, 2019, 05:30:09 pm
content: Quote from: Warhawk on February 10, 2019, 04:25:30 pmWell, I don't want LDOs for 1 cent, but I want LDOs that won't damage parts. Yes, the TPS70933, the TLV76033 and the TLV76050 were all tested on a PCB. The circuit is available on the 18th post of this thread.By the way, I've used the TPS70933 before. Never had a problem while connecting it to 5V. In your case, did you used 24V?P.S.: Schematic available here too. I'll change the regulator back to the TLV76050, unless I see and advantage using the TPS70950. For sure, I'll have to use a resistor in series with the regulator.Kind regards, Samuel Lourenço

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 10, 2019, 05:46:32 pm
content: I would send some failed devices for decapping and have a good SEM image taken from the die.Even though it will be identified as an “external EOS event”, the relative location of the event within the die can provide additional information about the nature of the failure. Specially if the EOS are always located in the same area.

author: Warhawk
author_rank: Frequent Contributor
timestamp: February 10, 2019, 06:13:23 pm
content: I use TLV70933in the applicationup to 18 V. I needed something with ultra-low standby current. I saw your schematic after I submitted my post and didn't see there anything wrong. What kind of power supply do you use?How long are the wires from the PS to your board? How do you enable the system? (turning on the PS, pressing the output on/off button or just connecting the banana plug?). Do you have any other testequipment (e.g. oscilloscope or a laptop) connected to your board? If so, is your output of the PS connected to the chassis, aren't there any grounding loops?First, I would take measurements on the regulator (Vin-GND, Vout-GND). You have the right scope for it. Just use single shot.Anyway, I really recommend you posting this on the E2E forum.PS: I understand that you're upset and probably frustrated (I am the same blood type) but take measurements first. For example, we have a linear PS from a reputable company in the lab which does spikes up to 60V after turn-on. We probably ship millions of these so I would be really surprised if they were systematically failing at 24-V.Regards, Jiri

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 10, 2019, 06:42:35 pm
content: Well, I'm just plugging and unplugging to an already on power supply. That should pose no issue. I'll try to get some scope shots soon.Kind regards, Samuel Lourenço

author: Siwastaja
author_rank: Super Contributor
timestamp: February 10, 2019, 06:49:56 pm
content: Quote from: bloguetronica on February 10, 2019, 06:42:35 pmThis poses a HUGE issue and will often kill any IC unless you design a correctly damped input circuitry. This is basically an RC snubber.Basics.Tim explained it very well above.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 10, 2019, 07:50:22 pm
content: My explanation seems not to have been read...The other thing that absorbs surge (and prevents reverse polarity) is a TVS diode. You want the TVS's peak voltage rated within the regulator's maximum, which is higher than the TVS's nominal rating by a modest amount. So a 30V regulator might need a 24V TVS.Again, this does nothing for overcurrent, which one should not rely on with such a tiny LDO, or really, in general.Tim

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 10, 2019, 08:08:00 pm
content: Ok, did some experiments by putting a 220resistor at the input. Did some short circuits upstream to the regulator, to create some spikes, and the TLV76050 held pretty well. Raised the voltage to 28V and used another resistor in parallel with the first one, this time it was a 82resistor. Again, it held. So I can assume that the spike issue is solved. A 100resistor works with some margin.Another issue, and that might have fried the AD5551, are the peaks during unplugging. By using 100nF capacitors at the input and the output, as described in the datasheet, I can observe peaks a bit larger than 6V, on some rare occasions after disconnecting. I can reduce those peaks by using 1uF capacitors. See the image attached. After the sample, I couldn't get peaks greater than 5.72V.Quote from: T3sl4co1l on February 10, 2019, 07:50:22 pmYour explanations were read. The 24V in the final application will be provided by an isolated DC-DC converter, which will be soldered onto the board. However, I'll still use a 100resistor in series with the input of the regulator just to be on the safe side. A TVS will serve no purpose there, because if the DC-DC converter outputs a peak, it will fry the diode plus the regulator.Kind regards, Samuel Lourenço

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 10, 2019, 08:12:00 pm
content: Quote from: bloguetronica on February 10, 2019, 08:08:00 pmHow sure are you of this? -- What's the converter's capability? What size diode did you have in mind?I have an application that uses a switching converter to dump six hundred watts into a trio of SMC sized TVS diodes. They take this abuse for almost a full second before simply getting too hot (I have thermal protection in the circuit). TVS diodes aredamngood at their job.Tim

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 10, 2019, 08:54:12 pm
content: Quote from: T3sl4co1l on February 10, 2019, 08:12:00 pmI think that this application doesn't need to have that. The DC-DC converter itself is well regulated. If something goes wrong, then the whole board is toasted. Anyway, I'm planning to use the resistor and perhaps a 1206L005 in series with the input of the regulator. It is a bit of over-engineering, but if the board comes with the 5V rail shorted right after soldering, I won't get damaged components. A TVS will be used, for sure, but only at the input of the board, along with a nice big PPTC fuse and a SCR crowbar.Kind regards, Samuel Lourenço

author: floobydust
author_rank: Super Contributor
timestamp: February 10, 2019, 10:31:00 pm
content: I would say almost every voltage regulator experiences overcurrent on start up while charging the output and load capacitance.Are we saying this IC shouldn't have to protect itself? It seems to be using die temperature for current limit...I've had some SMPS IC's fail due to input dV/dt being too fast. Like ignition key-on in a car, or plugging a banana jack to a bench power supply, it's a fast rise.Sometimes I wonder why yet another linear voltage regulator IC rolls out. Do you really need 573 parts in your portfolio?Linear Tech App Note 88Ceramic Input Capacitors Can Cause Overvoltage Transients. On a 24V wall-wart, spike is over 40V, and TVS, snubber etc. tried.

author: tszaboo
author_rank: Super Contributor
timestamp: February 10, 2019, 10:44:10 pm
content: Quote from: bloguetronica on February 10, 2019, 05:30:09 pmFYI, the LDOs dont damage the parts. The lack of input protection damages the part, and the lack of inrush current control.TI tells you this, there is nothing wrong with the part. The way you connect it that is the problem.http://www.ti.com/lit/an/slva670a/slva670a.pdfIf the 10uF capacitor has for example 0.1 Ohm internal resistance, then your regulator has to source 3.3A, which is a little bit more than it is capable of.

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 10, 2019, 11:07:49 pm
content: Quote from: floobydust on February 10, 2019, 10:31:00 pmCompletely out of the context. Precisely the opposite, it should protect itself and the load. When I see comments like this, I don't even bother reading the rest. However, the graphs were insightful.Quote from: NANDBlog on February 10, 2019, 10:44:10 pmI can confirm that a 22resistor in series and a 1uF capacitor in parallel after that seems to do the trick. Even a 4.7resistor and the same capacitor will help protect the regulator. It is a fact that this board, unlike other boards I've made, doesn't have a big electrolytic capacitor to help filter the spikes (I can't have one in the final application).Kind regards, Samuel Lourenço

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 10, 2019, 11:35:46 pm
content: Quote from: bloguetronica on February 10, 2019, 11:07:49 pmQuite in context -- if you want the regulator to do everything, you'll need to find one that's rated to do everything.If you just need a teensy little point-of-load regulator, you'd choose the one in question here.If you want something more robust, consider an old fashioned regulator (the power rating is higher, and the reliability is well understood), or something automotive qualified (often rated for high peak voltages, negative input and so on, and generally high reliability -- again, within ratings at least).No one part is suitable for everything, don't try to force fit something that doesn't belong. Just keep shopping, read datasheets very carefully.Tim

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 11, 2019, 12:40:22 pm
content: Ok, it seems that the resistor in series with the input does the trick. It limits the inrush current going to the regulator. The short circuit protection also works.Although, in the final application, this section will be supplied by a 8W DC-DC converter, I'll keep the 22resistor for two reasons:- The pass transistor Q2 is prone to cause transients when the load is a variable CC load;- The DC-DC converter will cause transients if it enters hiccup mode for some reason.The schematic for the test module is attached. I hope that there is no other phenomenon, like currents going from the OPA2180 input upsetting the AD5551, or the voltage regulator, and causing it to fail.As a final note, I stand corrected and the TLV760 series regulators are not a piece of crap. The inrush current to that 10uF niobium cap was taking its toll, along with the transients.Kind regards, Samuel Lourenço

author: Warhawk
author_rank: Frequent Contributor
timestamp: February 11, 2019, 02:51:22 pm
content: I am happy you could solve it. I simply love the world of electronics (no irony).Please consider changing the thread name. It hurts our sales

author: hans
author_rank: Super Contributor
timestamp: February 11, 2019, 04:05:47 pm
content: Let this be a lesson why you should always fully condition inputs and outputs to your boards.On your last schematic I still see that 24V line going directly to an OPA2180 amplifier, with some small capacitors attached. If you're confident those won't create nasty spikes during hot plugging (cable = L, cap = C, LC tank oscillator, as Tim pointed out already), then keep it like it is.... But I would connect that opamp after your 22R/1uF filter. It also will filter against mid-frequency ripples on your power supply.Input protection (ESD and TVS diodes) plus EMI filtering seems to be absent. Although this board only contains linear components, you don't want any oscillations or incoming switching noise be amplified to the outside world.

author: JPortici
author_rank: Super Contributor
timestamp: February 11, 2019, 04:21:00 pm
content: Quote from: bloguetronica on February 10, 2019, 02:57:05 pmYou must be doing something wrong, or i must be extremely luckyI found the TPS709A series to be reliable and capable to handle any stress i could induce in an automotive environment (I chose it because of the reverse voltage protection, i'm not always powering the boards from VBAT)

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 11, 2019, 05:13:31 pm
content: Quote from: hans on February 11, 2019, 04:05:47 pmThe idea is to test this as close as possible to what will be used in the final implementation. But probably, I'll have to use a PI filter after the DC-DC converter. The 22R resistor is there, as will be in the final application, just to protect the regulator. I think the issue might be caused by inrush current, and not by inductive spikes alone. In summary, a PI filter to smooth the voltage going to the whole system, and a local 22R resistor just for the regulator.Quote from: JPortici on February 11, 2019, 04:21:00 pmDid you tested that with 24V? Yes, the wrong I was doing consisted of not limiting the inrush current and neither filtering out the inductive spikes on power up.Kind regards, Samuel Lourenço

author: hans
author_rank: Super Contributor
timestamp: February 11, 2019, 07:39:52 pm
content: Quote from: bloguetronica on February 11, 2019, 05:13:31 pmThe 22 ohm resistor provides damping for the LCR setup that includes your board, wiring and input capacitor of the regulator.You can view this as the inrush current of the capacitor charging up it's voltage also simultaneously "charging up" the inductor's current. Namely, the inductor current will rise because the input potential is higher than the output. Once the capacitor voltage has stabilized, the inductor current has "charged up" to it's maximum, since both sides are now equal. However, for the "charged up" inductor current to dissipate, the inductor needs a negative voltage in order to do so. Since your bench power supply will probably be incredibly low impedance (it's not going to change), the voltage on the capacitor will increase. This "discharge cycle" of the inductor can cause the capacitor voltage to spike up to 2x it's nominal applied value. This is somewhat lessened by any quiescent loads applied on the circuit, so it's rare to see an actual 100% overshoot, but nonetheless it's something to take into account.If you hot plug this 30V (35V max) regulator into a 24V supply, you can expect that it will damage the regulator. Trust me, I've been bitten by this bullet very hard once that costed me about half a dozen fancy regulators and 2 prototype boards.The poles for a series LCR circuit are -R/2L +/- sqrt(R^2 - 4L/C). If you want a over-dampened system (i.e. no overshoots), you'll want to have R^2 - 4L/C > 0. With L=3uH (guessing you used roughly 3 meters of cable) and C=1.2uF, you get R^2>10, so a 3.3 ohm resistor should be sufficient. I read that you tested a 4.7R resistor also worked fine in protecting the regulator.See the attachments for the circuit in LTspice, then simulation with all series resistors 100m ohm (voltage source, inductor and capacitor), then final simulation with L1 having a series 3.3 ohm resistance. R1 simulates any small load that might be present, but honestly does little in this case.Counterintuitively, another solution would be to not use a ceramic capacitor, but a "crap" electrolytic capacitor instead.I don't think that the in-rush current on the output of the regulator is going to damage it. Namely the absolute max specs says that the output current is "internally limited". The device is thermally protected against long overloads. In my experience you will need to very grossly overload a part for it to fail instantly, and applying over 10V it's nominal rating can certainly cause it to very quickly degrade (i.e. a few power cycles) or instantly fail.

author: bloguetronica
author_rank: Frequent Contributor
timestamp: February 11, 2019, 09:11:06 pm
content: Thanks Hans! That is very useful. Probably, the PI filter I'm planning to use downstream to the DC-DC converter will be another reason to use the resistor. Although it will smooth out the switching from the converter, it will probably exacerbate the potential issue.Kind regards, Samuel Lourenço

author: Warhawk
author_rank: Frequent Contributor
timestamp: February 13, 2019, 10:01:54 pm
content: I would consider a TVS dide there too.