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In the manuala is stated that the maximum voltage on any pin is Vcc+0,5. This is clear.
But i am wondering if ther is protection diode inside the controller.
I mean that if ther is protection diode inside, that will limit the voltage level to vcc+0,5.
If this is the case, what is the maximum current that diode can manage.

The background to the question is as follow;
I am measuring some signals with the ADC and the signal is amplified with external operational amplifier (opa). The opa is powered with +10V power supply.
Can i just simply put some series resistance to output of opa and use that resistanse as current
limitter. Or if i have to supply opa with Vcc, to limit the output voltage to Vcc.
If i will power the opa with Vcc i have to use rail-to-rail opa.

- juha -

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Hello juha,

Sorry, but the ESD protection diodes are not meant to carry any current. I recommend designing you system so that this doesn't happen.

Morten, AVR tech. support, Atmel FAE

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Dear Morten,

Neverseless, please, answer on juha's question. I think it is interesting not only for the mentioned reason.

Thank you,
Varuzhan

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Hello again,

The maximum current the ESD protection diodes can stand, is 1mA. We never recommend a designed current flowing through these diodes, as this decreases their capabilities for ESD protection. Such a design will mean running the AVR out of spec, and thus losing our guarantees of its behaviour.

Morten, AVR tech. support, Atmel FAE

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Could you use a fast external clamp diode after the output of the op-amp?

Something like a 1N5819 Schottky diode, placed closer to the pin than the current limiter should limit the forward voltage to VCC+0.3v, which is below the major forward conduction region for the internal diodes if they are conventional PN-junction types.

This is quite a common configuration for medium-power outputs driving inductive loads like motors; it may also work on inputs.

Sean Ellis