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I am wondering what problems might occur if i reduced the voltage from the usual 5v down to 4.2v.

user2105725
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    What does the datasheet recommend? –  Sep 03 '18 at 17:22
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    @vicatcu That question was about running _outside_ of specified envelope. This question is about running well inside it. Not a duplicate. – Maple Sep 03 '18 at 17:23
  • Once again, this is **not a duplicate**. The referenced question was about running the chip in under-voltage condition. This question is about running the chip in valid power envelope per datasheet. – Maple Sep 05 '18 at 17:21

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The "P" in ATmega328P stays for "picoPower", which was Atmel's name for devices working down to 1.8V and possessing multiple power-saving features.

You can safely run the chip at maximum 20MHz down to 4.5V. Below that the maximum frequency starts dropping, approximately linearly down to 4MHz at 1.8V

There should not be a problem running at 16MHz at 4.2V. In fact, simple calculation suggests you can safely run up to 18.3MHz at this voltage.

See "28.3 Speed Grades" in the datasheet

Maple
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