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.