Protection diodes on NRF52832: max current

[Bwalker]

I'm developing an application using the NRF52832. Im using the ADC, and there may be times where the NRF52832 has 0V on its supply pin, but the voltage on the ADC pin is nonzero. I plan to put a resistor in series with the ADC input to limit the current through the protection diodes, so my question is, what current are these diodes rated for? I know that for most AVR devices, the limit is 1mA, but I assume it's lower for nordic?

[haakonsh]

Hey Bwalker,

We don't have a defined spec, but 1mA on ESD diodes is way too much, 1µA should be fine. 

Cheers,

Håkon.

[Bwalker]

Hi Hakon,

Do you think 10uA would be ok? 1uA is slightly too low for what I'm hoping to do.

Thanks,

Ben

[haakonsh]

Just to be clear, the maximum allowed GPIO voltage is VDD + 0.3 V. If VDD is at 0V the maximum allowed input voltage is 0.3V. If VDD is at 3.9V the maximum allowed input voltage is 3.9V. See Absolute maximum ratings. 

The reason I cannot say that 10µA is okay is because I honestly do not know. This is outside our tested and verified specification. 

If VDD is floating, a 5V input on a GPIO will result in the ESD diode conducting a current into the VDD net, thereby powering anything in that net at 5V - 0.3V = 4.7V, including the nRF52832 who will consequently break. You can try to limit the current going into the GPIO, but we cannot make any guarantees that the nRF52832 will perform to spec. 

[Bwalker]

Hi Hakon,

In this case, VCC is actually grounded, so the only real issue will be the diode current.

Thanks,

Ben