nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Kenneth — Mon, 08 Mar 2021 15:58:19 GMT

I have followed the case from time to time, but the case looked to be a more of a product design issue where you wanted suggestions on how to avoid flyback spikes to exceed the maximum electrical specifications stated in the product specifications. I thought using shotkey diodes seemed like a good suggestion, if you want us to perform a failure analysis on the chip to confirm where damage have occurred this is something we can do (I did also suggest this in my reply a month ago). We will need you to fill out a customer failure report before we can issue a return material authorization. Please create a new confidential case where you start with "Hi Kennneth" and link to this case.

Best regards,
Kenneth

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Protonert — Sat, 06 Mar 2021 21:39:57 GMT

I'm seriously disappointed in how this issue is supported by the Nordic team. Having been working for more than 20 years in the semiconductor industry, among others as Quality Manager, I have extensive experience on how companies serious about their product quality handle systematic issues like this. Doing everything possible to get back samples where such damages are observed and subjecting them to an in-depth failure analysis to be able to assess the root cause is a bare minimum requirement of customers I've been working with.

While other users offered explanations, none was forthcoming from Nordic.

Since the last few messages where we discussed a potential voltage spike due to inductive flyback, several other customers have reported same incidents. Inductive flyback now seems less probable, as the breakdown happened in application too where:

- the wires leading to the momentary switches were twisted

- either no LEDs were used whose wires ran parellel to those of the switch or the used LEDs were of different kind and number, drawing considerably less current.

This so far leaves a design weakness and/or an EOS purely coming from repeatedly changing input voltage on the GPIO pin.

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Protonert — Mon, 08 Feb 2021 21:19:09 GMT

Dear hmolesworth, thanks for your suggestion, it's not a long shot at all, although I do not have so much experience with inductive flyback as you appearently have, this was also our first guess considering a pure external influence. In case the board controls a programmable LED string the most common use case has the GND wire running parallel to the power wire, with the data line in between. It would be quite a challange to twist supply and GND, our customers would not accept such a requirement. It is also not known to us that other chips have similar problems, we used 8-bit microcontrollers from other vendors for similar applications in the past.

As to the inductive flyback, we considered a bit different scenario: suppose the two wires leading to the switch form a loop/circle and the LED string connector gets inside this loop, then during fast power transients voltage could be induced in the loop formed by the switch wires. This could happen considering that in the majority of cases the wiring of the LED strings and the swicthes go in the same direction for a certain lenght.

We tried to replicate this scenario but again it's a game of chances trying to reproduce it as long as we just guess at the root cause.

Nevertheless now having your valuable input I personally would narrow down the search scope to:

1. External influence: inductive flyback external to the board/chip

2. Internal influence: GPIO port logic where both input and output directions are enabled. Here I clearly wait for feedback from a Nordic engineer to help us figure out if such a situation where both input comparator and output push/pull stages are enabled could happen.

Generally speaking I'm amazed how many good inputs are coming from the community. I would be even happier if engineers from Nordic could take a more active role in the search for a potential root cause.

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

hmolesworth — Fri, 05 Feb 2021 16:12:07 GMT

Longshot, but you might consider inductive flyback due to the LEDs; the LEDs themselves have tiny inductance, but not so the interconnect wire which can be significant. Usually in an industrial application long wire runs or coils are run by using non-inductive layout. With a coil (such as a miniature sensor heater) this is done by folding the wire at the halfway point and wrapping the coil so the outward current path matches exactly the return current path. With a long LED string this is also of benefit, run the outward wire (3 volt drive) along (better still twisted with) the return current wire (typically the Gnd). That works only if the string uses an out-and-back pair of wires in a literal string; a star or ring layout is of course not so simple, and an out-only with some kind of distributed Gnd return is also a problem.

So a test; make an LED string using the same number and type of LEDs with a twisted pair supply and return and see if there is still a problem.

Fallback solution if this non-inductive configuration is not possible with your layout - try a reversed-bias schottky diode at the start of the LED string between the driven pin and Gnd. This may work as the inductive flyback spike radiated or conducted when the LED current is interrupted will couple a negative voltage pulse to the push-button lead and (if the push-button is closed) also to the input pin which will turn on the internal schottky clamp diode in the nRF52 and hence cause it to break down. A small capacitor on the input pin may also provide some limited protection.

The schottky clamp diode needs to be on the LED drive and return at the nRF52 end, not the push-button input pin. These notes apply even if there was no problem; inductively radiated noise should preferably be suppressed as they can (and will) affect other devices in close proximity.

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Protonert — Thu, 04 Feb 2021 20:58:29 GMT

Hi Dan, yes I did try a static test, even a cycling one with repeatedly pressing the button. However the chance of reproduction there is meager at best, since the exact root cause can only be guessed at. Same story with the duration of the stress.

The most important question is if such a damage is caused by something intrinsic or extrinsic to the board/controller.

It is hard to tell if the damage can happen with no LEDs attached. The LEDs are not attached to the damaged pins, but are programmed by other GPIOs. Although these LEDs, if there are many of them (we talk about 100-300) can cause considerable currents to flow, that alone does not explain a damage to an unrelated pin.

Yes, your research took you in the right direction, we are talking about Li-Ion powered portable devices. Charging circuit is part of the board. The LEDs are of course powered by the same Li-Ion battery as the board. We never use 5V on such LED strings, they can work reliably even below 3V...

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Dan Halbert — Tue, 02 Feb 2021 14:26:48 GMT

Have you tried a static test where you ground the pins in question, with a test program that sets those pins as outputs with pullups enabled? You could let it sit for a while to see whether the pins fail.

However, you mentioned that there are potentially many RGB LEDs attached. It would be important to do the test above with and without the LEDs attached, and have them doing some kind of dynamic display to vary the display and to introduce transients. Have you seen pins being damaged with no LEDs attached?

Based on my Internet sleuthing, I believe these may be LiPo-powered devices. Are the board and the LED strings powered from the same battery? Is there charging circuitry integral to the product?

If this is not a battery-powered device, I would note that we have seen some 5V supplies that produce substantial spikes when powered up. This can damage the LEDs, though we have not heard of microcontroller output pins being damaged.

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Protonert — Tue, 02 Feb 2021 09:47:52 GMT

Hi Kenneth,

If you wish for your internal learning I can provide a sample with the described damage for your failure analysis.

I can also send over a secured and encrypted channel the schematics and the layout for review (i.e. not in the public chat). However we did that already with no findings which could explain the damage. GPIO's are directly broken out, except a few which are connected to the gate of nMOS power drivers (but alas they are not the ones damaged). The switches simply short the GPIO to GND. We do not have splitted GND domains. Slight GND-bouncing can happen as many application cases use WS2812B neopixels, which depending on the number of LEDs can draw a few Amps. However I expect that this will cause recoverable malfunction instead of outright EOS.

Regarding the sleep current, yes, we have peripherals which also consume current during sleep mode.

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Kenneth — Mon, 01 Feb 2021 17:49:12 GMT

I think the best I can do here at the moment is to offer you a schematic and layout review if you haven't already performed that. It is very important that any GPIO is always within >GND-0.3V and <VDD+0.3V, so make sure that you have not connected inputs somehow to different power domains, though I assume the button here are simply shorting to GND when pressed, so not sure how that can happen. I don't expect you have split ground here any thereby don't have some ground currents, voltage potentials here. Exceeding the stated input range may damage the chip over time (EOS damage). If you want we can perform an failure analysis on the chips.

A sleep current of 150uA was very high, I assume you have external circuitry drawing much of this current?

Kenneth

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Protonert — Mon, 01 Feb 2021 16:07:52 GMT

The device damage happens with the board enclosed in an application casing. Therefore it is not an ESD event. We use ESD protection in our offices. The PCB has even additional ESD protection ICs on the USB. Switch is also not reversed, as it happened in multiple encasings (encasings are individual products the customer want to place the board). The switches also perform their intended function, but after a time - which is hard to quantify, somewhere between hours to months - there is a device breakdown. Therefore I conclude it is a case of a gradual degradation with a hard short circuit to GND at the end.

The board when running in active mode consumes a few tens of mA, depending on the state of the peripherals. But in deep sleep, with all the peripherals disabled, the whole board including the nRF52 consumes on average ~150uA (this chip is designed to be low power). Obviously a damaged I/O pin will increase consumption significantly in addition to being disfunctional.

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Nguyen Hoan Hoang — Mon, 01 Feb 2021 14:32:05 GMT

could that be the firmware crashes (exception interrupt) or go into a loop or something. When the MCU is running constantly, it consumes in the mA range.

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Kenneth — Mon, 01 Feb 2021 14:18:44 GMT

It's kind of the first I have heard this is an issue, for instance we have DK's produced in the thousands with momentary switched without any issue that I am aware of. However, if there is an ESD discharge though the pin, this will very likely damage the pin, so I recommend using an anti-static wrist wrap whenever possible. It's also possible to add an RC network and ESD diodes etc, but I would think this is mostly an issue when the bare PCB is exposed, and not when placed in a final casing. Is it possible you have reversed the switch somehow, such that the case of the switch is connected to the input?

Kenneth

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Protonert — Sun, 31 Jan 2021 11:18:25 GMT

We use the internal 13kohms pull up of the GPIOs, wnich pulls up the input of the coparator to Vdd. The chip is supplied by a 3.3V LDO.

RE: nRF52832 GPIO irreversible pin damage in application when used as a momentary switch sense input

Nguyen Hoan Hoang — Sun, 31 Jan 2021 03:17:16 GMT

At what voltage is the pullup ? What is the operating voltage ? do they match ? The max voltage is 3.6V. If you pullup higher, it is likely to fail over time.