DRV8434: PWM modulation frequency confirmation

Hi Allen,

Thanks for your question.

The DRV8434 does not use fixed frequency PWM for current regulation. The PWM frequency will depend on the decay mode used and microstepping mode used as well as which quadrant of the current the output is current waveform is in. 

For all decay modes other than STRC smart tune ripple control decay mode the yOFF can be programmed - see Table 7-8. OFF Time Settings in page-26 of the datasheet. The PWM frequency in these decay modes will be 1/ (tON + tOFF). tON is determined by motor L and R, VM supply voltage, IFS current setting and motor speed - BEMF voltage. 

For STRC decay mode the tOFF is variable which means the PWM frequency will also vary. This also depends on motor L and R, VM supply voltage, IFS current setting, motor speed - BEMF voltage and load torque on the motor. In this mode OFF time settings will set the ripple of the current, see Table 7-7. Current Ripple Settings in page-25 of the datasheet. 

If the customer desires fixed TOFF for PWM current regulation we recommend using the smart tune dynamic decay mode for microsteps and slow decay for increasing and decreasing for full-step mode. 

Allen Lu said:

customer will refer it for setting the filter circuit design

Where would the filter be connected, what type of filter and what is the purpose of this filter? Thank you.

Regards, Murugavel