Wiring up the MC33926 motor carrier (pololu.com/product/1212/) for the first time, and I have some unexpected behavior.
Using Parallax Propeller for logic control. 75:1 25mm Pololu gear motor (low power).
Using the following connections on the logic side (direct connections to GND and Vdd to simplify matters):
Vin: NC
GND: GND
Vdd: 3.3V
IN2: 3.3V
IN1: GND
D2: 8kHz PWM signal from Propeller
D1: GND
SF: NC
FB: NC
EN: 3.3V
SLEW: NC
INV: NC
On the power side:
Vin: 6xNIMH cell, well-charged (7.8V)
GND: GND
OUT1,2: motor connections
Here are the symptoms: if I set the PWM duty cycle to 100% (or simply connect the pin to 3.3V), the motor spins fine. If I lower the duty cycle to 75%, it slows as expected. If, however, I set the duty cycle to 50%, the motor stops completely. Checking with the oscilloscope, I get the following:
OUT1 follows IN1 as expected: IN1 HIGH => OUT1 HIGH and IN1 LOW => OUT1 LOW
OUT2 typically does the opposite of OUT1, but if they’re both in high impedance, this shouldn’t be a problem.
If I lower the PWM frequency to 800Hz, the motor runs better (all the way down to 10% duty cycle). Hooking up the SLEW to 3.3V doesn’t seem to help much (the motor turns a little faster, and you can see the faster rise time on the oscilloscope, but it still doesn’t run under 50% duty cycle).
I tried a desktop power supply with no improvement.