Electrical – ATMega8 get too hot when connect AVCC pin to VCC!


My ATMega8 gets too hot when I connect the AVCC pin to VCC, either I use a filter or not (I do use ADC). Why?? Anyone got the same proplem? I use a 7905 regulator to create 5V for the MCU, and it also gets hot right after I connect the AVCC pin (before that it only warm up a little). Please help! I burned out a ATmega8!

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Best Answer

The circuit would work almost as-is with another blocking cap at the input of the 7905, but the first change will most likely introduce another GND reference and thus a short via the ESD diodes in the pins.

Note that the circuit is missing the ISP connector which is more likely connected in a debugging environment. This could introduce the above GND/Earth connection which can fry the chip.