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

[Protonert]

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.

[Nguyen Hoan Hoang]

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.

[Protonert]

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.

[Kenneth]

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

[Nguyen Hoan Hoang]

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.

[Protonert]

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.

[Kenneth]

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