# AVR 1.1V Internal ADC Reference Over-Voltage

If I use the internal 1.1V reference for the ADC, and my Analog input exceeds 1.1V, lets say 2.5V, is that harmful to my microcontroller? Or will ADC value simply clip (to 0x3FF) at 1.1V?

For convenience, I am including an excerpt block diagram from the ATMega328 datasheet.

• Speaking from experience alone, not from datasheet references, so be careful: I've used internal ref and accidentally connected ADC pin to 4 Volts+ for hours. It'll clip, but won't kill the MCU. – Anindo Ghosh Dec 11 '12 at 19:42

• In the section "Electrical Characteristics" it lists the Absolute Maximum voltage on any pin except reset as being Vcc+0.5V. Then however, in the subsection on ADC, it states ADC VinMAX = Vref. So while I agree it seems as though maybe it's okay to exceed Vref, the datasheet is far from clear on the issue... – Peter Gibson Feb 16 '15 at 5:03