DRV8835 with 3.3V logic 3.6V motor supply

Support Motor controllers/drivers and motors
1

I must be doing something dumb. I tried using the dual motor driver carrier (md18a) to drive a pair of small dc brush motors, but had no luck. I powered the carrier with 3.3V and the motors with 3.6V. I tried both VIN and VM, the latter bypassing polarity protection. I connected GND to my common ground. I pulled MODE up to 3.3V with a 1K resistor. I connected the motor to O1/O2. I drove EN1/PH1 to logic level HI/LO and LO/HI. The motor didn’t run. I checked all voltage levels. Everything looked OK, but the O1/O2 levels didn’t switch to 3.6V/0.0V as expected. I tried two different carriers. Motors run fine when connected directly to 3.6V. What am I missing?

Edit: A generic toy motor worked fine, so the coreless drone motors must pull too much current for the drivers. Kind of surprising, since I was driving the coreless motors with 2N2222 before. I solved it by disconnecting the motor and measuring the unloaded O1/O2 voltage, which switched as expected. No problem, I will just use logic level MOSFETs with reverse EMF diode. That should work fine. I am not sure the specs on the coreless motors. Must draw a lot of current.

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2

The DRV8835 does have an overcurrent protection feature and we have encountered problems using them with small ceramic filtering capacitors on the outputs. Coreless motors have lower inductance than motors with cores which means the current can spike faster. It is possible that resistance of the winding in the motor is low enough to exceed the overcurrent protection trip level of the DRV8835 (1.6A minimum) at your supply voltage.

You might look at our BD65496MUV Single Brushed DC Motor Driver Carrier board instead. It will have a larger footprint for your application, but it can handle up to 5A peaks for several milliseconds.

-Nathan

3

Nathan, thanks. Mystery solved. :slight_smile: