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stm32L series adc question

Question asked by spectre on Jan 11, 2013
Latest reply on Jan 25, 2013 by Amel N
Hi to all,

I'm using a stm32L152V8 100pin 64k.the question regards the adc peripheral and the gpio of the mcu.

1)I'm putting an analog signal on the PA0 pin configured as analog input(this signal goes from 0v to a max of 3,8V(it's high,but read below)

2)I see that if the signal goes between 0v and Vref+(3.3v) everything works fine
(I read correctly from 0 to 4095 steps in the adc register)

3)When the signal goes over Vref+(but less than 3,8v),I suppose that the clamp diode starts to work and everything works fine (I still read 4095 steps in the adc register)

4)When the signal goes up to about 3,8v,I read in the adc register a strange value.So I need to clamp the signal outside of the mcu.

Preamble: I know that I must avoid to put a signal greater than vref+(3,3v),but I want to know if it's normal that the adc register value goes crazy when I apply a voltage around 3,8v on the pin.I've checked if I'm pushing too much current on the pin but it's not the problem.

I do this question because I was used with the st7 series to put signals with a little higher voltage value than vref+ on the pins without problems just using the clamp diodes inside of the mcu.