DRV8231: Insufficient motor torque.

Hi Randall,

I will look into this issue. Expect a reply from me within 24 hours

Regards,

Pablo Armet

Hi Randall,

Is there a higher capacitance capacitor tied to VM? it is recommended to have a 0.1uF and minimum of 10uF capacitor on VM. That's my only feedback on the schematic.  

Randall Shaffer said:

The torque output is not as expected and the current trip appears to be shutting the device down often

Can you send a waveform of nFAULT and output voltage/current? I need to confirm if the fault is OCP or due to another type of fault.

Regards,

Pablo Armet

Thank you for the schematic feedback, Pablo. There is 47uF on Vm. I will work on the waveforms.

Randall,

Thank you! I appreciate your patience.

Regards,

Pablo Armet

Hi Randall,

Randall Shaffer said:

The torque output is not as expected and the current trip appears to be shutting the device down often. Is the current sensor too large?

How much motor current you expected? The circuit design set the current limit at 2.5A.

Randall Shaffer said:

Should slow or fast decay mode be used?

It depends on the application, and I have no idea what it is for -- stop and go position control, or speed control as running a fan or pump? If it is a speed control motor with high inertial load, then don't use fast decay mode as it will pump higher into VM during pwm off cycle. No input then no output.

Brian

Thank you for the reply, Brian. The stall current of the motor is 550mA. I expected the current to be below that level. The motor is used for stop and start position control and drives a gear box.

Hi Randall,

Randall Shaffer said:

The stall current of the motor is 550mA. I expected the current to be below that level. The motor is used for stop and start position control and drives a gear box.

Where did you get the motor stall current of 550mA -- measured a stalled motor, or from motor datasheet? I don't understand that if the stall motor current is only 550mA, then why it caused the 2.5A Itrip to trigger?

If you wanted max motor current to be limited at 550mA, then the Vref or R5 (Rs) need to be changed to provide 550mA limit.

Brian

The value of 550mA is from the datasheet. I set the limit at 2.5 A to allow higher peak currents if I ran the motor briefly above rated voltage.

Tell us what is the condition that caused the 2.5A  Itrip to trigger? How much PWM duty and VM=? Did it happen when motor started moving from zero speed, or when pwm was given a large value?

Randall Shaffer said:

The value of 550mA is from the datasheet. I set the limit at 2.5 A to allow higher peak currents if I ran the motor briefly above rated voltage.

BTW, it is called continuous stalled current. The key word here is Continuous.

Brian

Vm = 12, PWM duty = 5/12 (it is a 5-volt motor). At this operating point there is insufficient torque. If I increase the duty ratio, the circuit stops functioning.

Randall Shaffer said:

Vm = 12, PWM duty = 5/12 (it is a 5-volt motor). At this operating point there is insufficient torque. If I increase the duty ratio, the circuit stops functioning.

A motor is not rated like a chip with VCC=5v; Yes, you can drive the motor at 12v if you wish, just make sure motor temperature is not exceeds the spec.

Please provide motor full datasheet if you want to resolve the issue. 

Brian

The motor is not being driven at 12 V but with PWM and a duty ratio of 5/12. Please find the motor data sheet attached.

kysan_motor_1150221-09.19.2022.pdf

Hi,

Pablo is out of office today. He will reply to you once he back.

regards

Shinya Morita

Why close an unresolved case?

Brian