NRF52840 powering itself from P.02

[riataman]

Hello,

We have a custom boards that powers a NRF52840 module from a 1.8v voltage regulator coming from a 3.6v battery. We also connected the positive pole of the battery to the P02 (AN0) pin with the intention of using the 1/6 gain mode and the internal 0.6v reference to monitor the battery voltage.

We are running into the problem that the whole nrf52840 is powering itself from that 3.6v feeded to P02 (and it's actually outputting that trough the vcc pins too).

It doens't matter if the P02 pin remains reconfigured after reset or the 1/6 SAADC gain is setup.

Would putting the external battery trough a voltage divider to top the voltage at P02 at 0.6v solve this issue? My only concern would be excessive leakage of current trough this divider/pin.

[hmolesworth]

You have a classic phantom power issue, have a look towards the end of this post which provides a description of what is happening. In some ways you might find a better solution is to throw out the 1.8 volt regulator and instead rely on the 1.3 volt internal switcher; the downside is that other devices on the 1.8 volt rail might consume too much power at some higher value but I observed an overall reduction in power on a design I recently completed. The up side is that now you can measure the battery voltage internally without using an external pin and voltage dividers or FET switches

[ketiljo]

Maximum voltage on any pin is VDD + 0.3 V. If you exceed this, the ESD protection diode will start to conduct and you will power VDD via the GPIO.