GPIO Power looping back to Vcc

[bhargav i]

Hi Team,

We have observed that without power supply we are seeing 1V power at board Vcc. Without giving power supply to board.

Why is this happening?

We measured GPIO pins at Evaluation board, we are seeing 3.3V high. when we connected our board with out power supply immediately we observed 1V across Vcc.
Why is this happening? Some of these lines are looping back the voltage to Vcc line.

Could you please check it with high importance.

May be similar to this,we have observed that the UART lines also carrying voltage to Vcc.

Board should not advertise any thing without power supply but with UART to USB connector it is starting advertising and Vcc measured 3V, UART lines carrying 3.3V looping back the voltage to Vcc.

Please let us know, does all the GPIO lines have protection diodes inside nRF chip across Vcc and GnD , which are making a path for VCC?

[awneil]

What else do you have connected to the board?

Yes, it is common that powered-up external peripherals can feed power back to an unpowered part - nothing specifically to do with Nordic.

When designing systems in which parts can be powered-down, while other parts remain powered-up, this is always an area that requires careful attention...!

[bhargav i]

Then how generally this issue would be addressed?

[awneil]

Make sure there are no reverse current paths; eg, using switches or blocking diodes, and/or enduring signals are in the correct states before powering down ...

[bhargav i]

At the end, we must power up the device first before connectiong GPIO lines from PC?

[ketiljo]

It's the ESD protection diodes that causes this. When the voltage on a GPIO pin is VDD + 0.3 V, they start to conduct and will lift VDD and power the device. This is why the max voltage on any pin is VDD + 0.3 V

So make sure you don't exceed this limit at any time.