Tool/software:
Hi,
Could you please let us know the below queries
1) Whether the Mosfet PWM switching frequency : 30kHz is fixed?
2) If it is not fixed, how to calculate the PWM frequency which is required to calculate the power dissipation of IC
3) Any internal dependency between Step frequency & Mosfet PWM frequency?
Regards
Soumya
Hi Soumya,
1) Whether the Mosfet PWM switching frequency : 30kHz is fixed?
The DRV8899-Q1's PWM frequency will very, depending on the supply voltage, motor parameters, and set tOFF time.
2) If it is not fixed, how to calculate the PWM frequency which is required to calculate the power dissipation of IC
The PWM frequency can be calculated with fPWM = 1 / (tPWM_ON + tPWM_OFF). tPWM_ON is determined by the voltage on VM, the set full scale motor current (IFS), and the motors parameters. TOFF has 4 settings which can be set in the CTRL2 register bits 4 and 3. In the case that smart tune is used, TOFF will be determined by the current ripple.
hopefully this image from the datasheet is a helpful representation of how the tPWM_ON and tPWM_OFF can affect the PWM frequency.
3) Any internal dependency between Step frequency & Mosfet PWM frequency?
The MOSFET PWM frequency is not directly dependent on the step frequency.
Regards,
Joshua
Hi Soumya,
The formula for tPWM_ON is provided in section 3.2 of our Sensorless Stall Detection With the DRV8889-Q1 app note.
Regards,
Joshua
