External I2C bus communicating when nRF9160 is powered down

[calebsmyth]

Hi,... =)

I am currently working on a design that has an nRF9160 being powered by a 3.7V Li-Po battery and an accelerometer as well as nRF52810. The I2C bus on the design is shared between all three devices and all devices on the design run of a 3V3 power domain. VDD_GPIO on the nRF9160 is set to 3V3 also.

To save ever bit of energy that is possible, from power on the only device that is powered is the accelerometer, we then use one of the interrupt lines on the accelerator to power on the other devices etc one of them being the nRF9160 by means of a MOSFET. On sleep the reverse of this happen by clearing the interrupt on the accelerometer and switching the MOSFET off.

My question is, if the nRF9160 is powered down, not in sleep, completely powered off, and there is activity on the I2C bus, does this have the potential to damage the nRF9160 as the SCL and SDA lines would be switching between 0V and 3V3.

Any questions or comments are welcome.

Thanks in advance

Caleb

[Håkon Alseth]

Hi Caleb

My question is, if the nRF9160 is powered down, not in sleep, completely powered off, and there is activity on the I2C bus, does this have the potential to damage the nRF9160 as the SCL and SDA lines would be switching between 0V and 3V3.

If the nRF is powered off (ie: VDD = 0V) these two I2C lines will try to power the nRF via the protection diodes inside the pad, and thus draw current.

Due to this, you will then exceed the maximum ratings: https://infocenter.nordicsemi.com/topic/ps_nrf9160/abs_max_ratings.html?cp=2_0_0_11

 

I would recommend that you isolate the I2C lines (level shifter that you disable or similar) if you want to continue with this solution.

 

Kind regards,

Håkon

[calebsmyth]

Thank you for your advice Håkon, much appreciated.

Caleb

[Håkon Alseth]

Happy to help. Let us know if you have any more issues or questions.

Hope you have a nice weekend!

 

Cheers,

Håkon