Need more 25kHz PWM pins

Hello there!

I'm making a fan controller for my PC based on the Atmega328p microcontroller (basically an Arduino Nano). MY problem is that I want to control 6-8 fans independently but the chip only has 6 PWM outputs and I can only adjust the fr4equency f 4 of them.

I've tried to use some PWM expander over I2C but I cannot find one that can go up to 25kHz. (the standard PWM frequency of 4 pin PC fans)

Do you have any suggestions to solve my problem?

Have you tried the PCA 9685?

I've looked at its datasheet but it says: "Each LED output has its
own 12-bit resolution (4096 steps) fixed frequency individual PWM controller that operates
at a programmable frequency from a typical of 24 Hz to 1526 Hz with a duty cycle that is
adjustable from 0 % to 100 % to allow the LED to be set to a specific brightness value."

It's good for LEDs but not quite so for standard 4 pin PWM fans.

You don’t HAVE to PWM 4-pin fans at 25khz.
The problem is that a lower frequency COULD introduce noise (whistles).
Did you try PWM pin 5 or 6 on an Uno (~1khz).