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Topic: Tension on shutted down gpio (Read 2 times) previous topic - next topic

retrolefty


The protection diodes are rated at 0.5V max forward bias - that's rather less that 20mA I think - or have I missed the right part of the specs?

Vf and Imax are two different specification for the internal clamping diodes. The first tells when it starts to conduct, the second how much current can conduct before damage.

Actually specifying the voltage is a rather poor way of doing this as forward voltage varies significantly across the operating temperature range.

Yea, the Vf spec is of just passing interest, we know that a 5 volt signal will fully turn on the positive clamping protection diode on a input digital pin on a 3.3 volt powered board, what we want to know is how much continous current the diode can withstand, that is the datasheet spec of interest.

Lefty


Matz

So can I protect the analog input only with something such as 10K series resistor? If true is a very good info. In alternative i think to use analog switch but i need something that when is power off go in hight impedance. Do you know some ic like this?

MarkT

Many things can be protected with a large resistor - so long as no appreciable current flow is needed.  A digital input in normal operation takes < 1uA so even a 1M resistor would allow it to function (but much slower than normal - 10k is more reasonable a compromise).
[ I won't respond to messages, use the forum please ]

Matz

And is also ok for and analog input?

winner10920

For an analog input don't go any higher than a 10k resistor but it should work to protect it the same, if you go higher it will negatively affect how fast you can do an analog read, in the datasheet it says best with source impedance <10k ohms

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