DRV10983: Big steps in RPM when making small changes to the speed command

Hi Ari,

Thanks for posting your question in MD forum. This is not how the device is supposed to operate. Relation between input duty cycle and output speed is linear. Can you tell us how you measured the speed in RPM? Did you read the speed from the register or measured using a tachometer or measured the frequency of PWM signal in FG pin?

Regards,

Vishnu.

Hi, Thanks for the answer. We measure the frequency of the FG pin. The big steps can also be heard from the motor sound.

Hi Ari,

Can you share some details about your end application? We think this sudden jump in the speed could be due to the torque profile of your end application. Is the load on the motor constant or dynamic? Also, what is the rated current of the motor?

Regards,

Vishnu

Hi,

We have a fan attached to the motor. It just moves air in the room. The load increases with the rpm, when the fan moves more air.

Hi Ari,

Can you share the motor resistance, rated current, BEMF constant (Kt), pole pairs and maximum speed? If the motor current is too low, we might see some error in the BEMF estimation and zero-crossing. This could cause some fluctuations in BEMF constant (Kt) and motor speed. Can you check if estimated Kt is stable at the duty cycles where the speed is bumping up? Estimated Kt can be read by reading the register address 0x15 and 0x16. Please check Table 9 (Page 44) in the datasheet for more information on Motor Kt registers.

Regards,

Vishnu