How is the LMD18245 chopping frequency calculated?
The RC sets the time the bottom switch is off and current recirculates in the motor winding and decays towards zero. The time the bottom switch is on and current ramps up is the other part of the chopping period. This time depends on a number of factors such as the input voltage, the motor L and R, the off time set by the RC, the current trip point, etc. During the off time, current in the motor winding decays away from the trip point. How long it takes the current to ramp back up to the trip point depends on how far the current decayed, the motor LR characteristics, the input voltage, etc. The LMD18245 only controls the off time.
