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DRV10866: Fails to start motor sometimes, when pulsing motor

lloyd konneker
Expert 1790 points
Part Number: DRV10866
Other Parts Discussed in Thread: , DRV10963

Using the DRV10866EVM (evaluation module board with motor provided in the kit) and a EZ MSP430 Launchpad (the USB dongle with separable target board.) I jumpered Vcc, Gnd, and a motorEnable signal between the boards. The MSP430 enables the signal for 0.1 second, then disable for 1 second. The signal from the MSP430 is taken from the same pin that drives the LED on the MSP430 eval board and drives the PWM pin of the DRV10866. Thus I am driving the motor full on for 0.1s, then full off for 1s.

->The motor responds say about ten times, and then quits responding. After spinning the motor’s shaft by hand, the motor resumes responding, for a while. When it does stop responding, it doesn’t seem to stop at any particular angle (at the resolution I can detect by eye, it could be it is always at an angle of a multiple of say exactly 90 degrees.)

I have powered the DRV10866 from the Launchpad’s USB driven power supply (5v?). In another trial I used a 2.8V battery. I also add a 1mF capacitor near the power pins of the EVM board (thinking the voltage was drooping and the driver entering under voltage lockout.) The battery leads are a few inches long.

I have tried removing jumper J2 (tying FGS to Vcc so that FG signal is 1/2 motor speed) with no change in symptoms.

I have waiting for more than 15 seconds, thinking it might be a false lockup detect that would expire, but motor never resumed responding.

While the motor is not responding, the FG test point seems to toggle low. I think this means the DRV10866 is trying to turn the motor (not in a locked up state.)

I see in another post a suggestion that the DRV10963 is a newer part. Is it a better choice for my application (just pulsing a motor very briefly say every ten seconds?)

I plan to try another smaller motor (the target motor is 3V, 10mm dia Maxon motor, but I don’t have one yet.) I plan to try other parameters, say ON a half second.

(Per Users Guide I have removed R6 to disconnect the DRV10866EVM  PWM pin from the EVM’S 555 PWM signal. I don’t have an oscilloscope.)

  • 0
    Expert 1790 points

    My theory is that the motor requires more than the 3.6V that the MSP430EVM provides (and that I tested with using a separate 3.6V power supply.) Unfortunately, I can’t find the data sheet for the motor provided in the DRV10866EVM (best I can tell it is an NMB Minebea of 25mm diameter. Datasheet for NMB Minebea current products that size don’t specify a minimum voltage, just a maximum voltage of 12V. The label on the sleeve in the DRV10866EMV says  "5V" but not whether that is a minimum, operating, or maximum.)

    Reading the DRV10963EVM User’s Guide, which discusses tuning the chip so the motor will start reliably. Does the DRV10866 suffer the same requirement to test the chip with a specific motor to determine how reliably it will start, without the possibility of tuning parameters of the chip? I want to call it a “resonance” problem: that a motor’s parameters mean that there are certain conditions (position of the rotor) where the parameters of the fixed(?) startup (in this case including an inadequate voltage)  just oscillate the motor without starting it.

    I will order the target motor and test it.

    I could use a stepper motor; I only chose the DRV10866 for its simplicity, and I guess that a BLDC is more efficient.