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

In my product I use certain GPIO pins configured as input with the pull up activated to act as sense inputs connected to momentary switches to control the application firmware.

Recently I had several incidents from my customers and fellow developers where GPIOs became irreversibly damaged.

In each case a GPIO involved was connected to a momentary switch (i.e. a mechanical switch between GPIO pin and GND).

The application worked fine until the point of breakdown, which means the GPIO was correctly configured as input with a pull-up.

After the damage the pin is stuck to GND. The devices affected have an increased current consumption (normal deep sleep current is ~150uA, which goes up to several tens of mAs for damaged chips.

In the application we use one or two momentary switches. On the one the momentary switch is depressed approx. 1% of the time in active mode. The other is depressed 10% of the time. Latter is more prone to an earlier breakdown, i.e. the degradation happens during the on state of the momentary switch, until the point of breakdown.

As using a momentary or latching switch on a GPIO is a standard use case for microcontrolllers, I would like to understand what could possible cause such damage.

The incident is unlikely related to my product and is also reproducible on a reference device (Adafruit nRF52 Bluefruit), therefore dependency on layout of board or influence of additional peripherals I can rule out at this stage.

Parents
  • 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.

Reply
  • 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.

Children
  • 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

  • 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.

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