51822 in the absence of power supply, work

[zcmm]

Hi，I have a question. the PCA10005 board's P0.17(Or other pins) connected to 2.8 v voltage,but the Vcc is not connected,and the PCA10005 GND connect to 2.8V GND.The PCA10005 work(Uart transmit data),and the Vcc is 2.03V.Why ?

[awneil]

You will be getting supply leakage through various internal structures in the chip; possibly also external circuitry.

This is not a good thing to do!

[Ole Bauck]

For example esd protection diodes.

[awneil]

Indeed: e2e.ti.com/.../back-powering-why-are-the-lights-on-when-the-power-is-off