nRF52840 RESET pin grounded

[RobHel]

Hello. I have designed in the nRF52840 into a product and we've seen this issue on at least two prototypes. The RESET pin seems to get stuck low (grounded) and I can't seem to recover it. Initially I thought perhaps an ESD strike damaged the IC, but now that this has happened twice, I find it less plausible.

In our schematic, the RESET pin is just tied to a programming flex connector, and an IC supervisor. I removed the supervisor but there still appears to be ~760 ohms from RESET to GND

 

I'm unsure if there's anything I should try here, or if it's safe to assume the IC is damaged. 

Thanks,

Rob

[Jared]

Hi Rob!

Some questions:

1. Have you flashed the devices with any fw or are they blank? Is the RESET pin feature disabled in your fw? By default it will be enabled.
2. If you measure directly on the RESET pin pad, is the voltage at 0V or does it float a bit over that?
3. What percentage of devices produced do you see this issue on?  

regards

Jared

[RobHel]

Hello. 

1. FW has been flashed many times on the devices. RESET is enabled (we use it for a low power scenario).

2. Voltage is about 60mV constant.

3. 2 units seen so far of the ~30 or so we've produced 

[Jared]

Hi,

On a non-working board, could you try replacing the faulty IC with a good IC to determine if the problem follows the chip?

regards

Jared 

[RobHel]

Yea I think that is the next step. I'll respond here when that gets done

[Jared]

Great, keep me posted,

regards

Jared