Using Current Limit on MAX14870

Hi Team,

I’m currently using the MAX14870 (Pololu #2961) to drive a 12V DC Medium Power gear motor (Pololu #3233). I am using a 12V supply and everything is running fine. However, I am interested in whether I can use the Current Limit feature on the MAX14870 to allow higher input voltages without destroying the motor. I know that this is how it works for stepper motors, and presume it works similarly with dc motors.

If I were to cut the trace add a 170mOhm Rsense resistor to the MAX14780 (set the current limit to 0.6A) would I be able to safely run this motor using an input supply voltage all the way up to the 36V specified as the MAX’s high voltage? Are there any confounding factors I should be aware of?

If this works as I expect, do you have a recommended method of choosing the current limit for any specific motor? I chose 0.6A above because that is the maximum tested current shown in the datasheet for this motor.


Hello, Ethan.

In general, I do not recommend supplying electronics with voltages exactly as high as the maximum they are rated for since that leaves no safety margin for noise or transient voltage spikes. Powering your motor from a higher voltage (even if you use the MAX14870 driver’s current limiting) will also make it harder to control your motor at lower speeds since you are reducing the range of useful PWM duty cycles and will have less resolution in your control.

As mentioned on the motor’s product page and in its datasheet, a general recommendation for brushed DC motor operation is to keep the current draw at or bellow around 25% of its stall current at its rated voltage. However, keep in mind that setting that kind of limit using a motor driver’s hardware current limiting will cap the current draw during the motor’s entire operation, which might have an impact if you try to make the motor accelerate quickly since that would normally involve the motor drawing more current for a brief period.

- Patrick

Great, I’ll test it of course but I think that is a tradeoff I’m willing to make. The most likely scenario is that I would use either a 12 or 24V supply on the system, so I shouldn’t approach the limits.

Low speed control and lower acceleration is good to know about, but probably isn’t a problem for my application.

Thanks for the info,

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