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DRV8305-Q1: max PWM duty cycle

Part Number: DRV8305-Q1
Other Parts Discussed in Thread: DRV8305


What is max PWM duty cycle of DRV8305-Q1 that can be implemented can be implemented for BLDC motor control?

What limits the PWM duty cycle?



  • Viktorija,

    This depends on both the needed input PWM frequency and duty cycle. There is a minimum time that the device will detect as a input, any less than this timing and the device input deglitch time will ignore the input. At a particular fixed input PWM frequency, that ON time is less the lower in duty cycle you go.

    I don't recall the minimum ON time for the PWM input pins but at less than 200kHz you should be able to get down to low PWM duty cycles without issue since this is what the part was designed for.

    If you have a certain PWM frequency and duty cycle of note I could check this for you.



  • Adam, 

    If customer uses 10KHz switching frequency what is the max/min PWM duty cycle they can implement on DRV8305 for BLDC motor control?

  • Hi Viktorija,

    We are having severe inclement weather in Dallas and multiple team members are without power. Please be patient with our response here.



  • Hi Viktorija,

    I will do my best to respond to your question Monday. Thank you for your patience!



  • minimum duty cycle calculations.xlsx

    Hi Viktorija,

    The minimum duty cycle that the driver supports at a 10kHz frequency depends on several factors, so I have included an excel spreadsheet that can be used to adjust parameters to calculate an approximate minimum duty cycle. The minimum duty cycle depends on the dead time for the device (minimum is 280ns), a 200ns delay between the input PWM command and the response of the gate command, and the rise and fall times for the switching of the MOSFETs. If you have a 250ns rise time and a 150ns fall time, then the minimum duty cycle would be equal to (200ns delay + 280ns dead time + 250ns MOSFET rise time + 150ns MOSFET turnoff time)/(100000ns period)*100% = 0.88% duty cycle. This duty cycle would result in the high side MOSFET turning on for 200ns per period (this is a result of the time between the change on the input until the signal appears at the gate)

    The maximum duty cycle that the driver supports is 100% duty cycle, but if the customer uses less than 100% duty cycle than it is necessary to consider switching times. This would create a maximum duty cycle equal to 100% - minimum duty cycle. Using our example above, they would be able to achieve a maximum duty cycle of 100% - 0.88% = 99.12%

    Please let me know if you have any questions,