DRV8323: Various PWM modes

Hi David,

Thank you for your question! Let me try to give you some help.

6x PWM: This is the traditional control method for BLDC motors, this control mode allows each of the six inputs to control each of the six FETs. This mode is most useful if you have existing software using a discrete gate drive solution because you can use your existing code with the DRV832x gate driver. Most new developments do not use 6x PWM since they can achieve the same motor control with less inputs using 3x PWM or 1x PWM.

3x PWM: This mode is intended primarily for sinusoidal control (or FOC type control). Each of the three 1/2-H bridges is controlled with one input, allowing for easy "High" and "Low" control of each 1/2-H bridge. In sinusoidal or FOC type control, however, typically there is a pretty sizeable MCU executing the algorithm.

1x PWM: This mode was designed to allow simple trapezoidal control of the BLDC motor. For the simplest control, you can tie Hall Sensor signals directly into the 1x PWM input and control the motor with one PWM signal. Trapezoidal control will not have as high efficiency as sinusoidal or FOC control, but does not require any complex control methods.

Independent PWM: This mode is not really intended for motor control. Most use this control mode when they want to drive several solenoid loads on the output, so they want independent FET control to drive high-side or low-side FETs.

Thanks,

Matt

Hello Chris,

Thank you for your question!

The motor speed is proportional to the applied motor voltage, this is controlled using the duty cycle of the input PWM. So the speed of the motor is proportional to the duty cycle. For example at zero duty cycle the motor is stopped.

The input PWM frequency effects the smoothness of the motor. Anything with a low PWM frequency (<10kHz) may cause noise and vibration (especially below 5kHz or for low inductance motors). However a high PWM frequency causes the external FETs to heat up more due to the increased switching loss. Most of the time an input frequency of 20kHz to 30kHz is chosen because it is above the audible range, causes smooth current regulation, and does not have too much switching loss.

Thanks,
Matt