ATmega328p not functional bellow 3.45V

Hello everyone,

I’m trying to build a standalone ATmega328p at 3.3V/8MHz.
I managed to burn the bootloder, I can upload sketches, and everything seems OK,
until the supply voltage drops bellow 3.45V!!!

Bellow this voltage the microcontroller seems to stop working.
Find attached a graph with two plots were the black plot represents the supply voltage
and the red plot represents the response of the “Arduino pin 13” (PB5),
while the microcontroller runs the famous “Blink” sketch.

The only external components I use is a 10K pullup resistor at the reset pin and an 8MHz resonator.
I found some relative topics opened in the past
(e.g. http://forum.arduino.cc/index.php?topic=317488.0)
reporting the same problem but I didn’t find a solution.

Is there something I can do to make the 328 work reliably at 3.3V?

Thank you

The only external components I use is a 10K pullup resistor at the reset pin and an 8MHz resonator.

You must have a bypass capacitor directly across Vdd and Vss, typically 100 nF.

However, it may be a clock or brown out detector issue. What are the fuse settings?

You want 2 bypass caps, one between Vcc and Gnd, other between AVcc and Gnd. AVcc should also be connected to Vcc if it isn't already (for reasons unclear to me, some instructions omit that connection, and/or the bypass caps). The bypass caps should be as close to the chip as possible (one of the few commonly encountered cases where layout really matters).

You might try using the internal 8 MHz oscillator, instead of the resonator.

Take a look at the fuse settings. The brownout detector may be set too low.
Nick Gammon has a sketch for reading them

crossroads probably meant to say “set too HIGH”. imo 1.8v works out very well for virtually all situations.

Good catch. Yes, set too High.

It's kind of an odd value for the brown out to kick in though, isn't it?

Post or check your fuses, maybe you are running at 16MHz and it becomes unstable at lower voltages.
3.45V doesn't look like a specced brownout voltage.