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MCF8315D: Measured rpm is lesser than 100rpm than target rpm in a certain situation.

Ernest Cho
Expert 3311 points
Part Number: MCF8315D


Hi team,

My customer is said that measured speed is lesser than their target RPM at the initial operation on MCF8315D.

For example, their target is 2600RPM but resulted 2500RPM, or 2800 target but 2700 result.

During some repeat, this issue recovered. But their software engineer didn't see this during his developments, it just happened on the set situation.

Is there any possibility that this phenomenon could occur?

Bests, 
Ernest.

  • 0
    TI__Mastermind 27447 points

    Hi Ernest,

    Is this test being conducted on a custom PCB now? The report indicates this issue was not occurring during the development phase (possibly on the EVM?).

    Could we enable the Saturation flag in the FAULT_CONFIG1 register? If this flag sets, it would indicate that the applied voltage is lower than required.

    The voltage may be dropping due to inadequate power settings at the source or insufficient decoupling capacitance.

    Let's measure the VM voltage using an oscilloscope probe to verify proper supply levels during operation.

    Thanks and Best regards

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    TI__Expert 3311 points

    Hi Venkatadri,

    They read VM_VOLTAGE and this is stable to 24.2~24.6V.

    They saw below fault flag. There's no saturation fault even setting the saturation flag.

    MTR_LCK : 1, 
    ABN_BEMF : 1,
    CONTROLLER_FAULT : 1

    BTW, the circumstance is in high temperature status and the setting is fixing at room temperature.

    Is it cause the abnormal BEMF, and ABN BEMF can cause the motor speed lower than the target?

    FYI, this test is conducted on customer PCB and also prior development phase test conducted on the customer PCB too. 

    Regards, 
    Ernest

  • 0 in reply to Ernest Cho
    TI__Mastermind 27447 points

    Hi Ernest,

    Abnormal BEMF flag will set if motor is stalled and not due to lower RPM.

    This issue is different, but the above issue mentioned is related to the reasons mentioned before.

    Can you share the JSON and customer PCB schematic?

    Thanks and Best regards

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    TI__Expert 3311 points

    Hi Venkatadri,

    I will send email to you.

    Bests, 
    Ernest

  • 0 in reply to Ernest Cho
    TI__Mastermind 27447 points

    Hi Ernest,

    Thank you, I will verify email and reply.

    Thanks and Best regards

    Venkatadri S