I'm looking to control PWM computer cooling fans directly from an ATTiny85, the fans want a ~15-25khz PWM signal.
The currant involved in minimal.
How minimal? It's extremely rare to find a motor that can be driven directly from a microprocessor. Or do the cooling fans have a "control line" separate from the power?
At default settings with Coding Badly's excellent arduino port
I got 500hz from pin0 and 1khz from pin1.
Are you running the processor at 16 MHz?
However from reading about AVRs in general it appears that far higher is possible
The ATtiny85 is capable of generating a 64 MHz PWM signal. So "far higher" is a good description.
just not doable through the arduino environment.
The Tiny Core includes a "veneer" that makes changing the timers a bit easier. Confirm the processor speed and I'll try to help.