What am I doing wrong? two DRV8838 failed

Support Motor controllers/drivers and motors
1

Hi Pololu and friends,

I recently picked up a couple of the DRV8838 motor drivers. I wanted to use them to drive 8 ohm coils for a kind of actuator I am building (with permanent magnets moved by the coils). I have only been using voltages from 3 - 5.5V on Vin and 5V at VCC. I see a max current draw of 500mA on my power supply for the motor voltage.

I use a low frequency 0-4V square wave for the Phase as I want the coils to flip polarity back and forth (around 1Hz up to 20Hz max). Each DRV8838 started working great, but suddenly stopped all function.

I poured through the support assist and added more capacitors to my power rails and tried again, but then my second driver failed. The datasheet highlights the protection circuitry so I was feeling pretty confident about this chip. Now I am wondering what I don’t know I am doing wrong.

Here is an image of the driver with Phase and Enable tied to VCC. With 5V at both VCC and Vin (separate supplies common ground) I get 0v on both motor outputs for both drivers.

drv8838 circuit
drv8838 circuit3024×4032 2 MB

Does this chip fail if the motor wires suddenly go open circuit? I know the chip prevents overheating like from shorts, but what about an air gap at the motor outputs?
OR
Is there a max frequency at the Phase pin? For instance it can only switch direction at 3Hz or something?

Thanks for any notes or thoughts.

2

Breadboard tracks are intended for logic circuits, and burn if forced to carry hundreds of mA.

I suspect that this has happened, and you now have intermittent contacts to the motor connections, which can lead to voltage spikes capable of instantly destroying a motor driver.

Don’t use a breadboard for high current (motor) circuits, and either solder the motor wires directly to the driver, or use driver boards with secure screw terminals.

3

Thanks @Jim_Remington I didn’t realize even hundreds of mA would do that. The voltage spikes kind of surprise me as I assumed even an ordinary motor or solenoid would generate these in normal operation. I saw another forum discussion about this driver on back emf protection. All the verbiage around this driver makes it sound really robust. Maybe a small bipolar capacitor in parallel with the motor will help? I’ve seen that used in e-waste tear downs.

Thankfully I picked up one other driver, the TB6612FNG. I’ll be prioritizing good wiring for sure!

4

Always a good idea to add noise filtering to brushed DC motors. Pololu has a blog article about that:

But you should not need to do that with actuator coils.