What am I doing wrong? two DRV8838 failed

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.

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?
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.

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.

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!

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.