I fried my MAX14870!

I have been testing my motor with the MAX14870 for a few months now. Starting very slow and gradually increasing the speed and load.

Yesterday I ran a poorly coded test which accelerated my motor to full speed much too quickly (nearly instantaneously). The deceleration was just as bad. The load complained loudly. Today, I can only run in one direction. Using the diode tester on my meter it is pretty obvious that I blew the M2 low side diode (and presumably the whole transistor). Another 14870 works OK. This was also my first full speed, long duration (60 seconds) test.

My motor is directly connected to the 14870. I was counting on the over current, over temperature and diode protection in the 14870 to protect me from - well, myself. Clearly that didn’t work.

What do I do next? Do I design in extra protection? Do I need a beefier controller? Or, just write better code?


Vin = 30v
I = 0.3 A @ 30% (well, that’s the design)
f = 23.4kHz
max duty cycle = 30%
load = about 50 lbs through an 8000:1 gear ratio


Your conclusion about what happened seems reasonable, and any of the approaches you suggested seem like they might be effective. If possible, my first recommendation would probably be to get a higher-power driver since that would give you a greater safety margin. If you can post a datasheet for your motor, I can let you know which of our drivers might be appropriate.

You might also check out the optional current limiting feature on the MAX14870; it is described in the MAX14870 carrier’s product page description.

- Patrick