In RPM mode when the fan’s speed is near the target speed, that is, when the TACH count is near the TACH target count, the control loop dynamics can often be improved by slowing the rate of change of the PWM dutycycle. This operates as follows: First, set a value for the count “window” and store it in the appropriate Window register. In RPM mode, calculate the difference between the current TACH count and the target TACH count. If the absolute value of this difference is less than the value in the appropriate Window register, the update rate of the PWM duty cycle is slowed to 1 LSB per second. When the current TACH count falls outside of the window, the duty cycle rate of change reverts to the selected value.