Issues/questions with the DRV8801 motor controller

I am using the DRV8801 to control some 24V DC Brushed motors. I am supplying the motors with 24 volts on the VMM pin, and 5 volts on the VDD pin. I am setting BRAKE to low (no braking).

What I am seeing is that when I send it a 0 on the PWM input, the OUT+ pin has 0 volts being sent, but the OUT- pin has 12 volts on it. Doesn’t seem right. Can someone explain?

Also, when I tie the BRAKE pin to VCC, the controller behaves more as expected - a 0 PWM gives 0 volts on both OUT+ and OUT-.

My second question has to do with the BRAKE pin. Can someone give me a sense of how much braking it will brake when it brakes? :wink: The reason I thought I should set it to low (no braking) is that I need to fairly rapidly change motor speeds (almost every half second). The wheels seem to slow down enough when power is removed that I didn’t think I needed additional braking, and it seemed like it might be better able to transition between speeds if it didn’t brake. But maybe not - I need to do further testing.

In any case, it doesn’t seem like power should be applied to OUT- when the requested speed is 0, regardless of the BRAKE setting.


- Dave

Hello, Dave.

The OUT pins go to a high-impedance state (floating) when both the PWM and BRAKE pins are set low. How are you measuring the OUT pins? Do you have a load connected to the driver when you are measuring the OUTpins? If you have a motor connected to the driver, does the driver cause the motor to move when PWM is held low?

When in drive-brake operation, the amount the motor will brake is dependent on the motor, so I cannot give you a sense of how much the motor will brake. We generally recommend drive-brake operation over drive-coast since it provides a more linear relationship between PWM duty cycle and motor speed than drive-coast and usually results in better performance at low duty cycles.

- Jeremy