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DRV10964: When PWM pin held high, does driver operate motor?

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Part Number: DRV10964

DRV10866 has this feature.  It is not clear to me from reading the datasheet that the DRV10964 has this feature.  IOW, does the PWM pin need to be pulsed high and low at some duty cycle less than 100% and some frequency less than 100khz (electrical characteristic FPWM in datasheet.)

I have tested this feature on the DRV10964, holding PWM high, and it does not appear to work, but there could be other reasons such as I chose a wrong motor or I have configured the open loop wrong. I am testing using the Mikroe "Brushless 2 Click" breakout board and a Nidec 10S BLDC motor ( a CD spindle motor, 12 ohm, 12k rpm, 12V).  When holding PWM high, a DRV10866 will drive the motor at 5V but the DRV10964 doesn't.  The test setup is also missing a bypass capacitor on the DRV10964.

  • Hi Lloyd,

    The DRV10964 can work with the PWM pin set to 100% duty cycle and does not need to be pulsed low. 

    Have you tried inputting 50% duty cycle into the PWM pin and seeing if it spins the motor? Is the DRV10964 attempting to start the motor or is it not doing anything?

    Regards,

    Michael 

  • In reply to Michael.Walker:

    Now that I know it should work, I will keep debugging.

    I have not tried 50% duty cycle.

    The motor twitches forward and reverse a few degrees.

    Power supply is a bench supply.  I just switch it on and expect motor to start.  Maybe I should add some bulk capacitance and a bypass cap (2.2uF recommended, not on the breakout board.)

    I reason that I don't need to get U,V,W in correspondence, since switching any two would just reverse the motor.  Maybe my reasoning is wrong.

    I have tried both a 3-wire motor without a common lead, and a 4-wire motor with a common lead (left unconnected.)

    Maybe the motors are too high speed.  Both are outer rotor type BLDC.  One is a no-name 28mm diameter motor for drones, the other Nidec 10S is usually a CD spindle motor (?) at 12k rpm.  I recall that the 10964 is for low speed fan motors?

    I am using a DRV10866 with success, but wanted to switch to DRV10964 to save the three resistors that simulate common lead for a 3-wire motor.  Not a big deal.

  • In reply to lloyd konneker:

    A duty cycled PWM signal DOES start and turn a Nidec 10S.  Whereas a constant high PWM does NOT.  Which might contradict what you say, just to be clear.  And to repeat myself, in my interpretation, the datasheet for the DRV10964 does not clearly say that a constant high PWM will operate the motor.

    To test constant high PWM, I tied PWM pin of the DRV10964 to Vcc, and just switched on Vcc via a TPS22860 load switch.  Maybe the PWM signal needs to transition high sometime AFTER the DRV10964 is powered up?  That is, its a timing issue.  For example "to start the motor at maximum speed, the PWM signal must transition from low to high at least X mSec after the DRV10964 is powered up."

    Here I express my wishes re EVM boards.  I wish there were an EVM for the DRV10964.  I wish the EVM for the DRV10866 had a jumper for the PWM signal to the driver chip.  (I modified my DRV10866EVM to bring the genereated PWM out and connected it to the Mikroe breakout board for the DRV10964.)

    Thanks

  • In reply to lloyd konneker:

    Two other motors, a 28mm no-name drone motor and a 16mm Yuneec drone motor, both start, spin for a half second, but then shudder and stop.  I am new to BLDC motors.  Is that a symptom of some sort of protection kicking in, or that I have misconfigured hand off from open loop to closed loop?

    For the latter, I recall the datasheet discusses high-speed motors and configuration, and I haven't rigorously configured yet.

  • In reply to lloyd konneker:

    Hi Lloyd,

    There is a DRV10964EVM: https://www.ti.com/tool/DRV10964EVM

    It seems that the problem is not that the DRV10964 will not attempt to spin the motor with PWM at 100% duty cycle but that the DRV10964 is failing to spin the motor with 100% duty cycle on the PWM pin. This could be because the motor is not something that the DRV10964 is good for spinning. you can use the DRV10963 and tune it for your motor or you could try to start the motor at a slower speed and then increase the PWM to 100% duty cycle.

    Regards,

    Michael