Problem using MC33926 in dual PWM mode (IN1+IN2)

I’m trying to control a Pololu 20D gearmotor via Arduino Nano and a MC33926. I’ve chosen to use the two-wire control method mentioned in the Basic Application Connections:
" The control lines can be reduced to two pins if PWM signals are applied directly to the two input pins with both disable pins held inactive."
(the above sentence could use a bit more detail on your product page - this is a bit vague for non-experts)

I’ve soldered jumpers to the adjacent pins on both D1 and D2 as well as the EN pin. Connections are as follows:

IN1: Arduino Pin D6
IN2: Arduino Pin D5
VIN: 22V

But the motor is not operating when I set the PWM inputs as follows:

analogWrite (D6, 200);
analogWrite (D5, 0);

I’ve confirmed via oscilloscope that I’m getting a positive PWM wave on D6, and D5 appears to be at ground.
However, for some reason both motor output terminals are at 22V. One should be at ground…

What am I missing here? Should I not be using analogWrite() for D5 (IN2) when I’m outputting a PWM signal on D6 (IN1)?



We spoke over the phone. From the call, it sounded like we determined the gearmotor probably was damaged because you were able to get another gearmotor to work on the motor driver. Also, your 20D gearmotor was not turning properly, and might have been damaged from being stalled at 22V before you had implemented current limiting to protect the gearmotor. I just wanted to check if you had any additional questions or problems.


Hi Grant, thanks for following up. Yes indeed it was the gearmotor damage - the board is still working fine now that I’ve swapped in a new motor. Thanks again for your help! I’ll try to post on the board today, sorry have just been super busy.
Btw, I’m exploring using these 20D motors for a commercial product that should be relatively high volume (2-5k units per year). So far the 20D motors work quite well from a form factor / size and torque perspective. The main problem is the noise (and potentially longevity, but we haven’t gotten to our stress testing phase yet…) They are quite noisy under load (although nearly silent with zero load). Is there anything that can be done to make them run quieter? I’m not sure if the noise is coming from the gear mechanism or from the motor itself, so I don’t know if the solution lies in better gears or in a more advanced motor controller system (certainly a sine-wave controller would help there, but definitely overkill for a tiny motor like this!)
Let me know if you have any thoughts on the above, or perhaps you can forward this to someone else on your team who could help?
Thanks again,Jeff

We do not have any good way of reducing the noise from the source, but you might be able to isolate the noise by enclosing the gearmotor. If the noise is coming from the gearmotor, I do not think changing the control scheme will help. I am not sure how you intended to use sine wave control, but it is generally used for driving brushless DC motors, not brushed DC motors.