max current for AVR IO protection diodes ?

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c_mcu_faq
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Posted by c_mcu_faq: Sun. Feb 12, 2006 - 12:04 PM
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in DS no information.

any ideas ?

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AVR Microcontrollers, megaAVR and tinyAVR
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Nuno
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Posted by Nuno: Sun. Feb 12, 2006 - 12:16 PM
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In an application note it is mentioned that it is 1mA. I don't have a link but it had to do with "crossing zero detection" of mains.

Edit: it's app note AVR182, page 3:
"The series input resistor is a 1 MΩ resistor. It is not recommended that the clamping
diodes are conducting more than maximum 1 mA and 1 MΩ will then allow a maximum
voltage of approximately 1,000V."

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c_mcu_faq
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Posted by c_mcu_faq: Sun. Feb 12, 2006 - 02:29 PM
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Thanks !

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ScottKroeger
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Posted by ScottKroeger: Sun. Feb 12, 2006 - 03:44 PM
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"in DS no information. "

In every data sheet's "Absolute Maximum Ratings" section, there is a spec for maximum "DC Current per I/O pin". It is generally in the range of 10s of mA. The collective input current for all I/O pins, plus the device operating current, must not exceed the "DC Current Vcc and GND pins. You must also make sure that your power supply won't float to excessive voltage if you source current into Vcc from I/O pins. As these are absolute maximums, I recommend derating by some amount.

The 1mA 1Mohm comment was taken out of context and may mislead you into compromising your design. I would not advise using a 1Mohm input resistor unless you really have 1000V input signals. Such high value input resistors will make the input pins highly susceptible to noise.

Limiting input current to 1mA under normal operation is probably not a bad idea, but if you are dealing with temporary fault conditions and wish to ensure no hardware damage (but potential software upset) the absolute maximum ratings are safe limits.

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