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MCT8329A: Motor starting problem

Seongwon Lee
Prodigy 20 points
Part Number: MCT8329A

Hi, recently I'm trying to drive the BLDC motor with MCT8329A.

I made a small development board myself and now I'm testing my board.

Since I don't use I2C communication with the IC, I'm driving the motor in default condition(analog driving mode).

So here's a problem with starting the motor.

The situation I'm in is like below in a row. I attached a video about the situation.

1. Successfully started the motor with 'Align'.

2. I applyed the analog signal after Vdc is stabilized.

3. The motor started running but It stopped after a few milliseconds(It even changes every time I tried. The longest drving time was around 1 second).

It seems like some kind of protection fault was activated since the nFault pin becomes low when the motor stopped.

Does anyone knows what's the problem in this situation?

Thank you.

  • 0
    TI__Genius 13920 points

    Hi Seonwon,

    To be better determine what could be the issue should you provide the following:

    1. A capture of one of the phase currents, SOx (if the DACOUT/SOx/SPEED_ANA is configured to output SOx), FG, and VM? 
    2. The register configuration that was loaded into the MCT8329A?
    3. The value of the external shunt resistor used for the current sense amplifier?

    Regards,

    Joshua

  • 0
    Prodigy 20 points

    Hi Joshua,

    Let me answer those questions.

    First, I didn't do anything with I2C communication(SCL, SDA pins are pulled up) so I guess everything is on default register setting.

    But I wonder there's a possibility that the register can be accessed and changed without I2C communication.

    Since I didn't change the register, DACOUT/SOx/SPEED_ANA pin is set as DACOUT pin so I don't use that pin.

    I applied the analog signal on SPEED/WAKE pin.

    I checked the FG pin and it works when the motor drives but what is VM pin? I can't find it in the datasheet.

    The value of the shunt resistor is 0.5 mOhm. Guess it might be so small that current sensing doesn't work properly but I have no idea what is the proper value so I chose a small one.

    Thank you.

  • 0 in reply to Seongwon Lee
    TI__Genius 13920 points

    Hello Seongwon,

    The registers of the MCT8329A can only be accessed over I2C. I cannot provide much assistance if I do not know the register configuration since many limit and fault configurations are set in the registers.

    Sorry, I got the PVDD pin name mixed up with the VM pin name on our other MCx devices. For the capture, not having a capture of the SOx pin is fine, please provide the phase current, FG, and PVDD voltage.

    Thank you for providing the shunt resistor value, the shunt resistor value along with register information can be used to determine if the current limits are set correctly. So that I can check the current limit settings, can you provide the motors max rated peak current?

    Regards,

    Joshua