No current flowing in GPIO pin?

lpcware — Wed, 15 Jun 2016 19:47:31 GMT

Content originally posted in LPCWare by DodigI on Sun Jun 08 04:12:01 MST 2014
Hello, can someone please explain this phenomena.

A GPIO pin is set as input with pull-up resistor enabled. Power supply is 3.3V. When I short the pin to ground a current of 55uA (60kR calculated pull-up value) is flowing through the pull-up resistor.
However, if I apply a 5V to the pin no current is flowing into the pin?! I would expect a current of ((5V-3.3V)/60kR) to flow, but I measure only 1nA (measured with a very precise source measure unit).

What is the catch here? I'm trying to understand how the ESD protection and 5V tolerant inputs work.. When the pull-up is disabled no current is flowing also, which makes sense if the pins are really 5V tolerant.

Thank you.

Re: No current flowing in GPIO pin?

lpcware — Wed, 15 Jun 2016 19:47:31 GMT

Content originally posted in LPCWare by 1234567890 on Mon Jun 09 00:20:09 MST 2014
The reason ist that the pull-x are no real resistors:
http://www.lpcware.com/content/forum/lpc1114-pull-updown-resistors-value
http://www.lpcware.com/content/forum/internal-pull-resistors

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No current flowing in GPIO pin?

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