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DRV8711: The phase current parameter of the motor is 4A but IFS is 4.5

Skylar Li
Intellectual 2000 points
Part Number: DRV8711

Hi experts,

   Nice to e-meet you! This is GREE FAE Skylar. 

   There is a question from GREE about DRV8711.  The phase current parameter of their motor is 4A. But when they tested their board performance, if they want to run the maximum speed of the motor, IFS should be set 4.5. If the IFS is not set 4.5, the speed of motor will be much slower.

  • The phase current parameter of their motor is 4A. Is this max value or RMS value?
  • Could you pls help tell me if the IFS is set to 4.5, will it lead to damage the motor?

    Look forward to have your reply. Thanks. 

BR,

Skylar

  • 0
    TI__Mastermind 45445 points

    Hi Skylar,

    Commonly stepper motor rated current is specified with motor operating in full-step mode. In full-step mode the motor current is typically a square wave which means peak and RMS values are the same.

    In microstepping mode stepper current is sinusoidal. With microstepping mode, to achieve close to the same torque output as in full-step mode, the sine wave peak current must be square wave peak current times √2. 

    1. "The phase current parameter of their motor is 4A. Is this max value or RMS value?". Like I said usually it is specified for FS mode and it is RMS. 

    2. "Could you pls help tell me if the IFS is set to 4.5, will it lead to damage the motor?".  This should be a question to the stepper motor vendor. When stepper motor is driven at the rated current it get hot very fast. The customer must pay attention to the temperature specification of the motor rather than the current specification. If the motor is driven at higher temperature for long duration this can affect the expected lifetime of the motor.

    Regards, Murugavel