DRV10983: Inductive AVS disabled, but still Voltage Surge is observed at 24V.

Hi Himanshu,

Thanks for posting your question in E2E forum. I believe you are working on a ceiling fan application. Since the inertia of ceiling fans are very high, mechanical energy of the motor is returned to the power supply when there is sudden drop in the speed. Can you enable mechanical AVS function and set AVSMMd to 0? In this mode, AVS is always active to prevent the applied voltage from being less than the BEMF voltage.

Regards,

Vishnu

Hi Vishnu,

Thank you for the prompt reply. Mechanical AvS is useful but since for some applications, I use Flux Weakening to achieve high rpm. In that case the Mechanical AVS does not allow me to work at low speed. To solve it KT has to be changed, which indeed means to design a seperate motor for the application.

Is there anything more that you could help me with this regard.

Himanshu,

I'm not sure on what you mean by "Mechanical AVS does not allow me to work at low speed". Can you provide more details to help me understand this issue? Is the device buffering the speed command to a value higher than the commanded speed? 

Another alternate solution will be to either add bulk capacitors across Vcc and GND or use TVS diode across Vcc and GND to prevent voltage surges at the input. 

Regards,

Vishnu 

Sorry for the delayed reply.

Yes, by low speed I meant that my speed command is as low as 40 but the speed command buffer still is at 100. The KT of the motor is fixed as the same motor is used elsewhere. 

We had already placed bulk capacitors across Vcc and GND of around 100uF nearest to it. We just wanted to know the response if the Bulk capacitors are not present or they are replaced by lower valued SMDs. For that we wanted to get the help of AVS and learn it's behaviour and change parameters if needed.

We removed our bulk capacitors to observe the AVS functionality of DRV but could still see the surges rise upto 46V and in some cases burn down the DRV, even when mechanical AVS with AVS to Vcc was enabled.

Is there anything more from DRV tuning that can help against surges ? And can we use 10uf cap , as suggested by datasheet, to avoid Vcc surges ? 

Himanshu,

Thanks for the details. I believe you see the voltage surge when you apply zero speed command. Can you try changing the closed loop acceleration to a lower value say 0.091 Vcc/s or 0.045 Vcc/s and issue a lower speed command (<15%) before you stop the motor? Decreasing the acceleration/deceleration rate and stopping the motor slowly will help dissipate energy at a slower rate and not cause voltage surge.

Regards,

Vishnu