The Rate of Change Control is a large factor in stable fan feedback in RPM mode. When the MAX31790 is trying to reach a programmed TACH count, it increments the duty cycle. The PWM Rate-of-Change setting in register 0x08 determines how quickly these increments occur. If the increments occur too quickly, there is a risk of overcorrection, which results in oscillations in fan speed. By programming the device for a slower ramp up speed, this decreases the risk of overcorrection.
Selecting a larger value in the Window register can also help to decrease oscillations. When the measured tachometer value is within the "Window" value of the Target TACH value, the MAX31790 slows the Rate of Change to 1 LSB to prevent overcorrection.