DRV8886AT: OFF time too long

Hi Aoyama-san,

"there is a ripple using Auto tune dynamic decay a little bit.
It seems a tBLANK is long. But the tBLANK is fixed as 1us."

This is probably due to the back emf of the motor, more than the blanking time. Zooming in to measure the xOUT1 and xOUT2 voltages will confirm this.

"When using Auto tune ripple control, the tOFF is long as 100us. It is audible frequency.

The customer are worried about PWM frequency down to audible frequency.

Is there any impact on sound noise of a motor?

I think there is no impact on sound noise because a motor coil is affixed and no viblation.

Could you give me any idea?"

The 100us shown in ripple control is not tOFF. Please zoom in to the area and capture the xOUT1 and xOUT2 voltages also. This will help identify which mode the device is in (drive or decay).

If the device is PWM'ing in the audible range, there could be some impact on noise. Also connecting the motor directly to the frame can increase the sound. Adding an isolator between the motor and frame can help.

Hi Rick-san,

Thank you for your reply.
I will ask the customer capture the xOUT1 and xOUT2.
I will let you know when I get results.

Best Regards,
Naoki Aoyama

Hi Rick-san,

I got results of evaluation.

I understood the tOFF is not too long using Auto tune ripple control.

I got results of evaluation using Auto tune dynamic decay, too.

DRV8886AT_xOUT.pdf

Do you have any opinion?

Regards,

Naoki Aoyama