DRV11873: To control the BEMF of DRV11873

Zhonghui Xu

Part Number: DRV11873
Other Parts Discussed in Thread: DRV10970

Hi team,

I got a question from customer.

"I am researching BLDC motor through your DRV11873.
In order to operate the BLDC motor at low speed using DRV11873, the PWM signal is being transmitted to DRV11873 using STM32. When the motor is operated in that way, when the PWM signal is transmitted, the motor initially rotates at high speed and then at a speed that corresponds to the PWM signal. Referring to the data sheet, I think we can rotate from the beginning at a speed that fits the PWM signal by analyzing the BEMF in some way, but I am leaving an inquiry because I want to ask for a detailed explanation.
Also, the current minimum speed is about 120 RPM, and I would like to know if I can rotate the motor at a lower RPM."

Thank you very much for your help.

Best regards,

over 1 year ago

0 Vishnu Balaraj over 1 year ago

TI__Mastermind 24405 points

Hi Zhonghui,

Did you try configuring FS pin low for low speed motor operation?

Regards,

Vishnu

0 Zhonghui Xu over 1 year ago in reply to Vishnu Balaraj

TI__Expert 5445 points

Hi Vishnu,

I just got feedback from the customer.

"I set the FS pin to low and tried to operate the BLDC motor using the PWM of DRV11873, but also when I started, I rotated at high speed for a while and then to the RPM that fits the PWM."

Best regards,

0 Anthony Lodi over 1 year ago in reply to Zhonghui Xu

TI__Mastermind 18480 points

Hi Zhonghui,

Thanks for the reply! Vishnu will look over this and try to get back to you by the end of the week.

Regards,

Anthony Lodi

0 Vishnu Balaraj over 1 year ago in reply to Zhonghui Xu

TI__Mastermind 24405 points

Zhonghui,

Motor speed initially overshoots because the device spins the motor in open loop to build sufficient BEMF and then enters closed loop and settles to the commanded speed.

Regards,

Vishnu

0 Zhonghui Xu over 1 year ago in reply to Vishnu Balaraj

TI__Expert 5445 points

Hi Vishnu,

Thanks to you, I understand that the initial speed of the motor cannot be helped.
Then is there no way to operate the motor at a speed below 120 RPM?

Best regards,

0 Vishnu Balaraj over 1 year ago in reply to Zhonghui Xu

TI__Mastermind 24405 points

Zhonghui,

Sensored motors work great at low speeds. Can you check DRV10970? This is a sensored trapezoidal control device.

Regards,

Vishnu

0 Zhonghui Xu over 1 year ago in reply to Vishnu Balaraj

TI__Expert 5445 points

Hi Vishnu,

Thank you for your answer.
A low speed operation of 100 RPM or less in a sensorless motor is difficult because the BEMF is not sufficiently formed.
Therefore, low-speed operation should be performed using a motor with a hall sensor.
Is that what you mean?

Best regards,