While researching minimum-voltage requirements of Uno, I came across what appear to be two datasheets for the ATmega328P:



Specifically, the power requirements (and processor speed for each power level) differ. How could I know which datasheet applies to the chip I'm using? I'm actually using an Arduino clone:

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  • It seems the first document is only for the 328P, and the other supports more (including the 328P). I would expect the information regarding the 328P is consequent in both versions (or should be). Oct 16, 2019 at 16:23
  • @MichelKeijzers: As can be seen in the photo, I am using a 328P. One of the datasheets states that the microcontroller can run at 1.8v @ 4 MHz, the other states a 2.7v minimum.
    – dotancohen
    Oct 16, 2019 at 16:25
  • 1
    I checked the revision history and the first talks about adding automotive, but sorry, I can't explain the differences. Hopefully adds a correct answer. Upvoted since I'm curious too now. Oct 16, 2019 at 16:28

2 Answers 2


You have ATmega328P-AU. Classic Uno with DIP socket has ATmega328P-PU. Arduino Uno SMD has Atmega328P-MU.

The automotive versions ATmega328P-15AZ and ATmega328P-15MZ have separate datasheet starting in Revision History with

Creation of the automotive version starting from industrial version based on the ATmega48P/88P/168P/328P datasheet 8025F-AVR-08/08. Temperature and voltage ranges reflecting automotive requirements.

  • Just to be sure: -AU does not stand for automotive? What does it stand for?
    – dotancohen
    Oct 16, 2019 at 19:08
  • 1
    the first letter is package form. -P is "Plastic Dual Inline Package", -M is "Micro Lead Frame Package", -A is " Plastic Quad Flat Package". I only read the datasheet
    – Juraj
    Oct 17, 2019 at 4:35
  • Thank you. I've gone through the second datasheet again and still cannot find that information, even when searching for the phrases you mention.
    – dotancohen
    Oct 17, 2019 at 19:41
  • 1
    @dotancohen, page 635
    – Juraj
    Oct 17, 2019 at 19:42
  • I see, thank you. I had no idea how to read that, I was expecting the information in another format.
    – dotancohen
    Oct 20, 2019 at 20:31

I think there is an error concerning the information about supply voltages. At least it's not consistent: microchip has separate websites for ATmega328 and ATmega328p. On the site for the ATmega328p it says: "The device operates between 1.8-5.5 volts". But the datasheet they link on the exact same site says: "Operating voltage: 2.7V to 5.5V for ATmega328p".

This is not just confusing, but contradictory and so I think the only one who can say for sure is the manufacturer.

Actually, the specified supply voltages are determined by the manufacturer by testing at various levels, but the device might operate even below or above this range (of course, a developer has to comply with the specs). The 2.7V rating could be an old spec and in the meantime they might have found out that the device indeed runs fine even at 1.8V. Maybe, they have just missed to apply this change everywhere this rating is mentioned, but that's just a guess.


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