nRF52832 one of output (p0.15) lost its power

[Damian]

Hi!

I have noticed strange problem with one of GPIOs - P0.15. We have tested 50 devices based on nRF52832 and 3 of them have problem with P0.15 after few days.

P0.15 pin we have connected with two 0603 small SMD LEDs with 100 Ohm resistors in series. Pin works as source for LEDs and is configured as output with drive mode NRF_GPIO_PIN_S0S1. Total current draw from pin is 2,72 mA in this configuration, voltage on this: 2,92 V. nRF supply voltage is 3,3 V. The LEDs are turned on only for 30 ms, every around 2 s.

After few days, LEDs does not provide appropriate light level in 3 of 50 devices. They have only about 5 % of its initial lightness.

Replacing nRF in device solved problem. When I solder damaged nRF to new PCB problem still occur so this is proof that problem lies in nRF.

I have made some more precise investigation and figure out that maximal outputted voltage on P0.15 falls to 2,36 V without any load in damaged nRF. When I take new nRF52 and solder into my device i have 3,3 V in same pin configuration. When I changed output drive to NRF_GPIO_PIN_H0H1 output voltage from this pin rises to 2,92 V without any load. In new nRF52 with NRF_GPIO_PIN_H0H1 also I measured 3,3 V.

This P0.15 pin lost some part of its power, without any interaction from our side. Anybody have any idea what is the reason of this problem? We have to know the reason because this really affect our product further development. This is serious problem when pin lost its power by itself.

Thank you for your help in advance.

[AmbystomaLabs]

I think you should double check some of your assumptions.

With 100 ohm series resistance and 2.72mA per LED then Vf is about 2.7V. While blue and green LED's generally have a high Vf, red and yellow are normally around 2v. A good sanity check would be to measure the current going into your complete circuit. Should be about 2x2.72mA plus nRF current of maybe 1mA.

Also the manner in which you are driving the LED's is not recommended practice. While the nRF can drive about 5mA per GPIO in high drive mode, you cannot haul 5mA x 20 gpio across the device. There is a limit to how much current you can drag through the core of the nRF.

The recommended practice is the have the gpio active low with the LED current coming from external source that is the same voltage as nRF input. Then the drive current doesn't have to go through the nRF.