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DRV8801 PWM voltage


I’m trying to drive a 16v DC motor with the DRV8801 and a WeMos micro controller. The Vbb is 16v but the max voltage available to the motor seems only 5v. Is this normal or am I doing something wrong here. The impedance connected to the motor seems to have a resistance of about 7ohms and hence the current would be a little over 2A.
I would assume this should not impact the Vout to the motor.

Please help…I see some similarity between my issue and the one listed here but couldn’t get my responses there.



Hi, Shankar.

When driving a motor with 100% duty cycle you should see the full motor input voltage across the motor. You mentioned expecting your motor to draw over 2A, but the driver can only handle around 1A continuously, so what you are seeing might be due to your driver overheating. Have you tried measuring the output voltage with no motor attached? If you do that and still do not see 16V across the motor outputs, could you post pictures of your setup that show all of your connections and solder joints?



Thanks for the response Claire…I’m glad my basics are ok… As for the voltage, I replaced my motor source (was a 16v wall wart) with a 11.1v Lithium Ion batter on battery and still don’t see the 11 or close to this voltage at the motor terminals.
The max I get in this condition is a little less than 5v and if the motor input is changed to a 9v batter, I get about 2.5v at the motor terminals.

For the PWM, I’m using pins D2 and D1 for DIR and PWM respectively…will send pics shortly.



Since the voltage you are reading decreased when you decreased your supply voltage I am suspicious that your controller is PWMing the driver and you are seeing the average of that on the output with your meter. Could you disconnect all the connections between your WeMos except VDD and GND and then try connecting the PWM pin from the driver directly to VDD?



Sorry about the delay in responding. Yes, you are right, I see the entire Vmm to be available on the motor output pins when I connect the PWM to Vdd. I’m a little perplexed now. Why would the controller do that? I’ll try and sent the relevant pin on WeMos high and check the voltage on that…Any pointers why this is happening and how to correct?
thanks again


If your WeMos is telling the driver to go at anything less than full speed, it should use PWM to effectively lower the voltage across the motor terminals. If you see the full supply voltage at the motor outputs when the WeMos pin outputs a constant high, your system is likely working as intended.



Hi Claire,
I was able to figure out the issue, thanks to your leads. Turns out one of my PWM pins of the WeMos controller wasn’t working as expected. I changed the pin and measured the voltages as suggested and all is well.
Thanks again…still can’t get the “coast” function to work.that’s for another day…


I am glad you got your driver mostly working. I would be happy to help you troubleshoot your coasting issue. When you are ready to look into it, please post details of how you have tested the BRAKE/MODE1 pin and what makes you think it is not working.