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

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 

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.

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

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.

I was assuming that the open loop portion of the starting sequence would obviate the need for external ramping up of motor speed by ramping the frequency of the PWM.

As I said earlier, one of my goals was to eliminate the resistor parts to simulate a common motor lead, required for the DRV10866.  If I must add parts back to generate a ramping PWM, there is little point in changing the design to the DRV10964.  The DRV10866 seems to start all the motors with PWM pin held high, while the DRV10964 does not.

Its an edge case, most users would already have an mcu or similar to control the motor.  In my case, I just want the motor on or off.

And don't trust what I say here, I am also trying to run a 12V motor at 5V, maybe that is the problem, although it works fine with the DRV10866.