MP6538 test board drive BLDC Current abnormal

Motor Drivers/Sensors
1

Title: MP6538 Evaluation Board Shows ~2A No-Load Current at 24V – Request for Review of Gate and Phase Waveforms

Hello MPS Team,

I am currently evaluating the MP6538 on a custom motor driver board and have encountered an issue with unexpectedly high no-load current consumption.

Test Conditions:

  • Supply voltage: 24V

  • PWM frequency: 25kHz

  • Duty cycle: up to 100%

  • BLDC motor running under no-load condition

Observed Results:

  • Our previous motor driver boards draw approximately 0.15A under no-load operation.

  • The MP6538-based board draws approximately 2A under the same no-load condition.

  • The motor already reaches its no-load speed at approximately 70% PWM duty cycle.

  • Increasing the duty cycle from 70% to 100% produces little additional speed increase, but the input current remains much higher than expected.

To investigate the issue, I measured the gate drive signals and phase-U voltage waveform.

Waveform Observations:

  1. High-side and low-side gate drive amplitudes are approximately 12V–13V.

  2. No obvious overlap between high-side and low-side gate signals is observed.

  3. The switching transitions appear generally clean, although some ringing is present during switching events.

  4. The phase-U voltage waveform shows expected PWM switching behavior.

  5. No obvious abnormal oscillation or gate-drive malfunction is visible from the captured waveforms.

I have attached:

My questions are:

  1. Is a no-load supply current of approximately 2A expected under these operating conditions?

  2. Do the attached gate-drive and phase-voltage waveforms indicate any abnormal behavior?

  3. Are there any known MP6538 configuration, layout, or gate-drive considerations that could result in significantly higher no-load current consumption?

  4. What additional measurements would you recommend to identify the source of the excess current?

If necessary, I can also provide:

  • Complete schematic

  • PCB layout

  • MOSFET part number

  • Additional oscilloscope captures

Any suggestions would be greatly appreciated.

Thank you.

2

Hi,

Thank you for posting on the MPS Technical Forum.

The MP6538 has a sleep mode, which will disable the device and draw very little supply current. It sounds like you could benefit from this feature.

Looking at your schematic the nSLEEP pin is always pulled up. In order to put the device into sleep mode, you need to drive this pin low.

I do not see anything blatantly abnormal from the scope shots you have provided.

Can you share a little bit about your application for the diver? Like when does it need to be driving load verses when is there no load?

Thanks,

Allison

3

Hi Allison,

Thank you for your continued support.

At this point, the load device is not yet ready, so we have only performed no-load testing.

We found that the motor current under no-load condition is much higher than that of other driver boards we have tested:

· Other driver board: 0.15A

· Our MP6538 board: 2A

Could you please help advise what might be causing this significant difference?

Thank you.

4

Hi,

Yes, the 2A is abnormal. This could be caused if the hall sensors are miss wired onto the controller causing the phases not to commutate correctly. There are six different ways to wire the hall sensors, and only one configuration will yield correct phase commutation.

I would recommend trying all the different ways to wire the hall sensors. I would also recommend looking at the phase output voltage. If there are issues with commutation, you should be able to see it there.

Let me know if this helps.

Allison

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