ATtiny85 - fuctions at 3.3V but overheats at 5V

I am running two ATtiny85s side by side with similar code that flashes an LED in morse code. One is on a break-out board attached to the breadboard while the other is simply the ATtiny85 chip wired to V+, ground and using a single digital pin output. The odd thing is that the break-out board 85 works at 5V happily while the bare chip overheats without functioning. Dropping supply to 3.3V disables the break-out board while the bare chip functions correctly (even after a what I thought was a fatal overheating). The fact that the breakout board needs 5V is not a problem.

My search for answers so far indicates the 85 is happy with 3.3V to 5V. I am using the internal oscillator only. I cannot understand the heavy current (heating cause) at 5V when there is no significant current flow on the digital output pin (it drives a LED through a 220R resistor). I suspected some type of self-oscillation or a short, but cannot identify either at work here.

Very puzzling. I appreciate any suggestions for further troubleshooting of the problem using a 5V supply.

What do you mean 3v3 disables the breakout? Attiny can work at 3.3v.

It is always a good idea to have an 0.1 uF bypass cap across the power supply leads, as close to the chip as possible.

mart256: What do you mean 3v3 disables the breakout? Attiny can work at 3.3v.

I meant that the ATtiny on the breadboard does not function at 3.3V. I understand the device is speced for the range of 3.3v - 5.0v, which is why I am puzzled with one device working only at 3.3V and the other device functioning only at 5V running the same code.

Dropping supply to 3.3V disables the break-out board...

BOD is very likely set to 4.3V.

Post a schematic.

Thanks for the ideas. Will add additional bypass caps at the Vcc pin and check on the BOD settings. Will also obtain/build a variable power supply to determine the precise voltage levels at which each device begins to function and stops functioning correctly.