Maximum voltage on default state pin on nRF52840

[GT]

Hi,

We are using nRF52840 MCU in High voltage configuration with DCDC enabled. We would like to measure the battery voltage which varies between 3.7 to 4.2 using a simple voltage divider as shown below.

We would like to set the BATEnable pin to low using MCU(current sink on GPIO) when we would like to measure the voltage at BATsense using internal ADC, and at other times, we plan to set both BATsense and BATEnable pin to default state(which will be floating). By this configuration we assume that there will be no current drawn by this circuit when no measurement is performed.

But when we are not performing the measurement and when  the battery is full charged, the floating pins will have a voltage of 4.2. (which will be equal to VDDH)

Is this ok from hardware perspective?  will this cause damage to MCU?

Regards,

GT

[Turbo J]

GT said:

the floating pins will have a voltage of 4.2. (which will be equal to VDDH)

No, it won't. There is a diode from the pin to VDD, which will start conducting waaay sooner.

Your circuit won't work without a proper high-side switch (e.g. p-channel mosfet).

[Dmitry]

GT said:

We would like to measure the battery voltage which varies between 3.7 to 4.2 using a simple voltage divider as shown below

Is there a reason not to use channel 0x0D (VDDH/5) of SAADC to measure VDDH?

[Kenneth]

Many good comments here already, you can also check out this blog post:
https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/measuring-lithium-battery-voltage-with-nrf52 

But when we are not performing the measurement and when  the battery is full charged, the floating pins will have a voltage of 4.2. (which will be equal to VDDH)

Is this ok from hardware perspective?  will this cause damage to MCU?

 This is not okey no, it may cause EOS over time.

[GT]

Yes. Because VDDH is not equal to battery voltage during charging.

[GT]

Thank you. We have now changed the design.