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MCT8316A: Some questions about the chip behaviour

Goran Ekstrom
Prodigy 65 points
Part Number: MCT8316A

Hi,

I have some questions about the chip (the AV variant):

1: How does the chip power on work? During chip power on I occasionally got some fault bits set. Will the chip do some power up tests and then await a start condition ot will it just "start running with what it has", i.e. the default register contents?

2: When are the VOLT_MAG, DC_BUS_CURR and DC_BATT_POW fields updated by the chip?

3: Will the ALGO_CTRL1 register accept multiple bits set, i.e. execute several operations at once, e.g. CLR_FLT and CLR_FLT_RETRY_COUNT?

4: Is the DRVOFF pin just an immediate, raw disconnect of the MOSFETS or will the controller do an orderly halt/start when the pin is updated? When activating the MOSFETS (DRVOFF to low), is there any timings required before issuing speed commands?

Regards

Goran

  • 0
    TI__Expert 5578 points

    Hi Goran,

    Thanks for your question on the Motor Drives E2E Forum. 

    I will aim to provide an answer on this by the end of the week!

    Best,

    Robert

  • +1 in reply to Robert Wedan
    TI__Expert 5578 points

    Hi Goran,

    1. The first step is to check for speed command and receive the PWM signal. If the speed is zero then the device stays idle until given a speed command input. Please reference the Motor Start Sequence Section of the datasheet (8.3.10 Motor Start Sequence (MSS)) for further details on this process.

    2. VOLT_MAG, DC_BUS_CURR and DC_BATT_POW fields are updated when the device receives a speed command and the motor starts to spin.

    3. Yes, the ALGO_CTRL1 register will accept multiple bits set.

    4. Yes, when DRVOFF pin is driven 'High', MCT8316A stops driving the motor by turning OFF all MOSFETs (coast state). When DRVOFF is driven 'Low', MCT8316A returns to normal state of operation, as if it was restarting the motor. DRVOFF does not cause the device to go to sleep or standby mode; the digital core is still active. Entry and exit from sleep or standby condition is controlled by SPEED pin.

    This is safe for the device and should not damage the device. There is no timing requirements except that DRVOFF must be driven 'Low' before the speed command can be received.

    Best,

    Robert

  • 0 in reply to Robert Wedan
    Prodigy 65 points

    Thanks for the answers. One more:

    The LOCK_ABN_SPEED setting is in Hertz. The FG pin and motor speed status register also outputs the motor speed in Hz, or Rotations Per Second. However, if the settings for LOCK_ABN_SPEED is also in Rotations Per Second, the resulting RPM is truly abnormal; 15000RPM as lowest threshold. How should I use LOCK_ABN_SPEED?

    Regards

    Goran

  • +1 in reply to Goran Ekstrom
    TI__Expert 5578 points

    Hi Goran,

    The LOCK_ABN_SPEED setting on the MCT8316A monitors the speed continuously and at any time the speed exceeds LOCK_ABN_SPEED, an ABN_SPEED lock event is recognized and action is taken according to the MTR_LCK_MODE. Threshold is set through the LOCK_ABN_SPEED register. ABN_SPEED lock can be enabled/disabled by LOCK1_EN.

    It is only meant to catch abnormal speeds. Depending on your application, it may not be useful for your system. However, we see systems >100,000RPM and in those applications we see customers use this feature's configurability to their advantage.

    Best,

    Robert

  • 0 in reply to Robert Wedan
    TI__Expert 5578 points

    Hi Goran,

    If there are no more questions, could you please help mark this thread as resolved?

    I will close the thread for now, but feel free to open it again if you have an additional question around this topic.

     

    Best,

    Robert