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DRV11873: The device start by PWM

Genius 5480 points

Replies: 2

Views: 42

Part Number: DRV11873

Dear all

      1.  I find the DRV11873 device must be started at high signal on the PWM pin, after 1~2 seconds time, the DRV11873 device can be controlled by PWM signal with 20% ~100% duty, otherwise can not be controlled. 

           I want to know this is normal ?

      2.  When the speed is 2000, the power consumption is 500mW, is it normal ? 

  • Hi,

    The expert of this device has been notified and will reply shortly.

    Regards,

    Michael 

  • Hello Went Cao,

    Thank you for your patience, let me answer your questions below:

    1.  I find the DRV11873 device must be started at high signal on the PWM pin, after 1~2 seconds time, the DRV11873 device can be controlled by PWM signal with 20% ~100% duty, otherwise can not be controlled. I want to know this is normal ?

    This sounds like the Start Up behavior on the DRV11873. I'll give you a summary and post the actual datasheet text below:

    The DRV11873 has an algorithm to blindly start commutating the rotor. The goal is to get a large enough Back Electromotive Force that the DRV11873 can read and the 150 degree algorithm can start driving the motor. Essentially, the device will try to step through a cycle of commutation looking for 4 continuous, and successful, zero crossings. This is considered "open loop operation", where device will not respond to the user's input command (i.e. there's not a feedback loop to the user's input command).

    In addition, the PWM pin doesn't necessarily need to be "high" or 100% duty cycle, it needs to be a large enough to meet the electrical characteristics of the PWM pin to start the process. Once this is initiated, the open loop starts and the phases are driven to 100% (regardless of the PWM input) and the cycle will start. Finally, once 4 continuous crossings are found, the device enters "closed loop" (i.e. output speed responds to user's input command). Then the speed can be controlled.

    1-2 seconds seems a little long for this to occur but, you could confirm this operation if you probed the phase voltage and phase current during this time. You would need to find 4 successful zero crossings of the current, and then FG will toggle, and the motor speed will start to rapidly accelerate to your target speed command. FG toggling signify's the start of closed loop operation.

    2.  When the speed is 2000, the power consumption is 500mW, is it normal ? 

    Speed and current depend on the motor's load and the inherent motor parameters. These make the power consumption calculations very difficult to predict. Motors usually have a rated unloaded speed and a rated voltage. If the voltage (VCC) is fully exposed to the motor (100% duty cycle), and the speed is close (80%-100%) to values in the datasheet, then I would consider the operation "normal". 

    Best,

    -Cole