Hello Forum, I need your help!
I made a circuit that moves a 24V 3A DC Motor with a DRV8801 motor Driver. I have the sense output connected directly to ground. A microcontroller ramps up a 31KHz PWM on the Enable Pin (To limit the startup current of the motor). If it detects an Fault signal, the PWM is started at 0 and ramped up again. The IC is making overcurrent faults when the current is <2A. I attached an 1 Ohm resistor before the motor and measured the current with an oscilloscope. The cursors are located at 3V, showing the 3A theoretical minimum peak current limit of the DRV8801, where I am expecting the OCP to trigger.
After the fault is detected, the motor stalls and the current is increased again because of the pwm ramp up. The voltage on the resistor looks much more noisy when I am driving the motor with the H-Bridge than when I drive it with a DC source. This is the graph of the motor being drived by the H Bridge:
I also captured a graph showing the motor current at the same resistor, powering it with an external supply and no driver. The spike is when the motor starts lifing a weight. The voltage over the resistor has also much less noise than with the driver.
Does anybody has an Idea if the fault is produced by noise in the current? The datasheet says something about putting inductors in series to the motor, can this be a solution for me? How do I have to size them?
Thank you very much for your help, and have a very nice weekend!