nRF5340 IO pin injection current

[dyoung.mpd]

Hi,

I have an nRF5340 design that uses the ADC to monitor an external voltage.  In some operating scenarios the external voltage may be present prior to VDD at the nRF5340.  The monitored voltage is divided down using two 100K resistors before it is connected to the nRF5340 (refer to attached image).  The monitored voltage has a maximum value of 4.2V at the input to the resistor divider.

Is there a maximum current that can be safely injected into an IO pin of the nRF5340 and does it vary by IO pin type?

Are there other potential faults that could occur if current is injected to an IO pin prior to application of VDD such as a corrupted boot sequence or lockup of the SOC?

Thank you for your support.

Sincerely,

Doug Young

[Kazi Afroza Sultana]

Hello Doug,

"In some operating scenarios the external voltage may be present prior to VDD at the nRF5340" - This is not good as it is out of specification (https://infocenter.nordicsemi.com/topic/ps_nrf5340/chapters/recommended_op_conditions/doc/recommended_op_conditions.html?cp=4_0_0_9). Maximum voltage (for recommended operating conditions) on a pin is Vdd + 0.3 V. When VDD is 0 V, max is 0.3V and the chip will be powered via the ESD diode. Maximum ratings (VDD value is -0.3 to 3.9 V) are the extreme limits to which the chip can be exposed for a limited amount of time without permanently damaging it. Exposure to absolute maximum ratings for prolonged periods of time may affect the reliability of the device. So, it will not be a good design.

Thanks.

BR

Kazi