3.6V on nRF51822 GPIO,14uA sink current ok?

[Dylan]

I'm attempting to use a GPIO configured as no-pull to determine if a 5V line is connected to the board for charging a battery. I have the 5V line going to a GPIO through a 100k resistor. Bus power to the nRF51822 is 3.3V, and I measure 3.6V at the GPIO... so 1.4V dropping over the 100k means the GPIO is sinking 14uA. It's a low amount of current to sink through the overvoltage protection diode, and the datasheet indicates a Vmax of VDD + 0.3 on the GPIO. Even though it's not advised to leave pins at max voltage for long periods of time, I feel that the constrained current would make it relatively safe. Does anyone have any insights or experiences around this?

Thanks!

[Ole Bauck]

If the spec says max VDD+0.3, then don't go over it. Yes the protection diode will sink the current to VDD, but that doesn't mean you can do it.

Why not use a voltage divider from the 5V source such that 3.3V is seen on the pin whenever the 5V source is there?

[Dylan]

I agree with you. That is my preferred design, but this has been a discussion with a colleague and I wanted to get some outside opinions on the matter. Thank you for your input.