#avr Logs

Dec 06 2020

07:26 AM fstd: so i've put around 6.5V on an ADC input of an atmega8 running at 5V
07:33 AM fstd: this likely to cause any permanent damage? the adc channel seems to still work..
07:33 AM fstd: absolute maximum rating says VCC+0.5..
07:48 AM rue_bed: it depends if the protection diodes just pulled vcc up
08:00 AM fstd: rue_bed: can you elaborate please?
08:47 AM twnqx: fstd: there are clamp diodes in the IC that will push excess voltage into your VCC rail
08:47 AM twnqx: it's more about limiting the current then
08:48 AM twnqx: there's a circuit that uses an AVR stright on 230VAC to detect zero crossings
08:48 AM LeoNerd: Spicey
08:55 AM fstd: twnqx: thanks for the explanation. the 6.5V came from a 1 kOhm source, so I guess I'm good
08:57 AM fstd: holy crap that direct mains connected AVR is an official atmel application note
08:57 AM fstd: so that isn't even a hack?
08:58 AM fstd: (i mean it is connected via an 1M resistor, so if the input impedance is low enough i guess it would end up below the rated maxima?
09:01 AM fstd: ...but no way an adc input would have low enough input impedance..