Hello team,
My customer tries to calculate switching loss on DRV8885 with referring to app note, slva504.
To calculate switching losses we need fsw information according to the app note.
Could you let me know fsw value for DRV8885? Is it step frequency for DRV8885?
Best regards,
Sato-san,
The PWM frequency is different than the STEP frequency. For example: customer can stop the STEP pulse and make the output current stay on a certain level. In this case, the STEP frequency is zero. But, the PWM frequency is how many the high side FET and low side FET switching cycles are in 1 second
The PWM frequency is equal to 1second/(output current rising time+output current falling time)= 1 second /(output current rising time + toff)
Since the output current rising amplitude is equal to the output current falling amplitude. So, the output current rising time is related the decay mode setting which is related to the output current falling amplitude in toff. It is hard to give a simple equation since the motor back EMF is related to the motor speed. If the input voltage is high, the motor speed is low and the output current falling amplitude is small (slow decay), the PWM frequency is dominated to TOFF. The maximum frequency is lower than 1/20us=50kHz.
Regards,
Wang Li
