DRV8353RS-EVM: Questions about DRV8353RS 3x PWM mode (INLx control)

Hey Ashish,

Ashish Pokhriyal said:

In 3x PWM mode, should the INLx pins (INLA, INLB, INLC) be driven as simple GPIO signals (static 0/1 per commutation step), or are they also intended to receive PWM waveforms?

• In other words, is the recommended usage:

  • INLx = 0 → phase off (Hi‑Z)

  • INLx = 1 → phase enabled, with the actual sourcing/sinking selected only by INHx,
    and INHx alone carries PWM if that phase is the “high” phase in the step?

The INLx pins do not need a PWM signal, you can use the gpio signals to put the phase in active or hi-z  mode, based on the datasheet truth table.

Yes INLx = 0  is hiz and inlx = 1 is phase enabled but inhx determines if on or off

Ashish Pokhriyal said:

In 3x PWM mode, is PWM intended or recommended to be applied only to the high‑side control inputs (INHx) of the sourcing phase, while the corresponding low‑side of the sinking phase is kept continuously on (INLx = 1, INHx = 0)?
Or is it valid / recommended to apply PWM on the INLx (low‑side) inputs as well?

Yes, 3x mode is utilized when you want to only use 3 pwm signals and let the driver take care of the remaining logic. These PWM signals are applied to the Highside inputs.

If you have enough pwm signals and want to have the full control of each mosfet then you can use 6x PWM mode. 

Ashish Pokhriyal said:

NOTE: Does driver itself create a complementary of pwm in 3xpwm mode ?

Yes. See the gate on HS and LS switching in table below:

Best,

Akshay

Hi Ashish,

That will depend on the motor, since that will depend on the inertia required to align the rotor, along with the strength of the permanent magnets on the rotor, along with the load on the motor along with the magnitude of the align current. I would recommend running testing with the motor to determine how long the align current should be applied. The worst case load condition should be considered since this will slow down the time it takes for the rotor to align with the applied magnetic field. You can apply the align current for a certain time and can increase it or decrease it until it fully aligns within the time every run no matter the starting rotor position. 

Regards,

Anthony Lodi

Hi Ashish,

For an overview, you can refer to this video: https://m.youtube.com/watch?v=S28P3ZTD9ws

It is a bit high level, but let me know if this helps.

Regards,

Anthony Lodi

Hi Ashish,

This app note covers sensorless trapezoidal control and should be a helpful reference. Since it was last updated in 2015, the parts discussed are older parts and are generally not the latest recommended parts from TI, but the algorithm information should be helpful.

https://www.ti.com/lit/an/sprabq7a/sprabq7a.pdf?ts=1766763558605&ref_url=https%253A%252F%252Fwww.google.com%252F

Regards,

Anthony Lodi