DRV8837EVM: DRV8837 PWM problem

Part Number: DRV8837

Hi

I try to use the coil with a PWM of motor drivers. But there are some problems.

I use stm32f1 MCU, IN1 : 80% 400hz, IN2 : 0% 400hz PWM

output of the coil is abnormal...When you see the picture, the signal of OUT 2 is not zero..

Normally, OUT1 is 80% PWM and OUT2 is near 0???

Why are IN 2 and OUT2 different??

Hi Lee,

Sorry for the delayed response about the bulk capacitor. Yes, .1uF (100nF) is probably too small. Please increase the cap.

Please start with 10uF in parallel with the .1uF.

Hi Rick,

Thank for your response.

Yes, I replaced it larger than before. It's a little bit less noisy, but there is no significant change in the output signal.

And I tried to replace the Rod(coil) with a DC motor. In addition the diode(H-bridge) was attached to prevent a backEMF. but it is the same symptom.

Hi Lee,

"Why are IN 2 and OUT2 different??"

When IN1 is set to a logic 0, the outputs are disabled. Current that was flowing through the FETs now flows through the body diodes of the DRV8837.

To maintain current flow OUT1 goes below ground and OUT2 goes above VM. Eventually, the current will decay to zero and the voltages will become equal.