Hi All, talking about datasheet for Atmega328p, for analog comparator the input offset voltage is specified as Typ = <10mV, Max = 40
So I understand that normally it will be less than 10 but can go up to 40 in some cases and will vary a little bit chip to chip, but my question is: Does this value change much with chip aging, temperature cycling, etc.
For example I have Atmega328p on the protoboard, powered from battery through liner regulator at regular room temperature, etc. I measure input offset voltage for analog comparator and is 8.5mV, can I expect this particular chip have this input offset voltlage forever or it may change up to 40 let's say 1 year down the road?
Does this value change much with chip aging, temperature cycling, etc.
That's a "good question".
Everything that's analog will vary with time & temperature and randomly. There will be short term variations (noise) and longer term variations (drift). But, I wouldn't expect it to change much... If it's 8.5 now it will probably never hit 40. I wouldn't expect it to very by a factor of 2, but those are just guesses.
40 is not just the chip-to-chip manufacturing variation but it includes ageing and all other effects. If you took the "worst" chip from the production line and tortured it with the maximum voltage and temperature for years, it probably wouldn't reach 40.
Of course the manufacturer cannot test every combination for years at a time so many values like this are calculated or estimated.
Min and max are usually across the full operating temperature range of the chip, its worth checking any footnotes to the specifications for such details. Variation with temperature can be surprisingly large for some parameters.
If you always design for the worst-case specification, you will have fewer unpleasant surprises!
You need to study the data sheet and as stated design for worse case. Many of the parameters are not necessary measured but are by design. In your statement design for 40, and be happy when it is less. As long as it is less then 40 the part has met its specifications and is good. It is your responsibility to take this into consideration in your design. I question how you made your measurements, at that voltage you need specialized equipment, at as minimum you need at least 4 digits to the right of the decimal point, preferably 5. Also critical is the mounting parameters, circuit boards have leakage, capacitance, etc. As you get into this you will begin to understand how a chip can be damaged but still appear to work. If the internal leakage went to 80 most applications will never know but this will continue to degrade and it will fail, momentary or 20 years probably somewhere in between. This is typically the path ESD takes and why we use grounding equipment. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil