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MCF8316C-Q1: Question for MCF8316C-Q1 Block

Alex Wang
Prodigy 140 points
Part Number: MCF8316C-Q1
Other Parts Discussed in Thread: MOTORSTUDIO

Tool/software:

Hi TI,

In the datasheet, Motor lock, Hardware lock, and Software lock are mentioned, which makes me a little confused.

1.Are these three locks always enabled during usage of MCF8316C-Q1?

2.What are the differences among these three locks? Could you kindly give some instances?

3.There are 2 design requirements in our product:

(1)one is stall detection

I think it could be achieved via LOCK_ILIMIT. We configured LOCK_ILIMIT to some value which is bigger than the rated peak current, held the motor rotor to stationary state by manual, and we could see LOCK_ILIMIT fault on MotorStudio. I want to confirm if this stall detection method is right or not;

(2)the other is speed abnormal detection

For example, the motor is spinning at the target speed 600RPM, someone tried to press the motor rotor and slow down the speed to around 500RPM, could MCF8316C-Q1 detect this speed abnorma default by itself?

I tested Abnormal BEMF (ABN_BEMF) mentioned in section 7.3.22.13.2, but I could NOT get ABN_BEMF fault when I tried to hold the motor rotor and slow down the speed.

Thanks,

Alex

  • +1
    TI__Mastermind 26610 points
    Alex Wang said:
    1.Are these three locks always enabled during usage of MCF8316C-Q1?

    These locks can be configured to be either enabled or disabled and the response to the fault detected by the lock can be adjusted. Software Lock can be adjusted with LOCK_ILIMIT_MODE, Hardware Lock can be adjusted with HW_LOCK_ILIMIT_MODE, and the Motor Lock can be adjusted with MTR_LOCK_MODE.

    Alex Wang said:
    2.What are the differences among these three locks? Could you kindly give some instances?

    Software lock takes the measured phase current output by the MCF8316C's internal Current Sense Amplifier (CSA), passes it through an ADC, and uses software to determine if the phase current has exceeded the threshold set by LOCK_ILIMIT.

    Hardware lock takes the measured phase current output by the MCF8316C's internal CSA and uses a comparator to determine if the phase current has exceeded the threshold set by HW_LOCK_ILIMIT. This detection method will have less delay for detection than the Software method.

    Motor Lock can detect multiple faults which are used to indicate if the motor is stalled including the measured speed or BEMF not being close enough to the expected speed or BEMF.

    Alex Wang said:
    I think it could be achieved via LOCK_ILIMIT. We configured LOCK_ILIMIT to some value which is bigger than the rated peak current, held the motor rotor to stationary state by manual, and we could see LOCK_ILIMIT fault on MotorStudio. I want to confirm if this stall detection method is right or not;

    The method you used with LOCK_ILIMIT to detect a stall condition can work. When the motor is in closed loop operation, the MTR_LOCK fault can also be used to detect a motor stall state.

    Alex Wang said:

    (2)the other is speed abnormal detection

    For example, the motor is spinning at the target speed 600RPM, someone tried to press the motor rotor and slow down the speed to around 500RPM, could MCF8316C-Q1 detect this speed abnorma default by itself?

    I tested Abnormal BEMF (ABN_BEMF) mentioned in section 7.3.22.13.2, but I could NOT get ABN_BEMF fault when I tried to hold the motor rotor and slow down the speed.

    Can you check if the setting of SPEED_LOOP_DIS and CLOSED_LOOP_DIS? If both of these settings are set to disabled then the motor will not detect these faults.

    For the ABN_BEMF fault, setting ABNORMAL_BEMF_THR to 70% sets the greatest threshold for allowable BEMF difference. You can try setting this threshold lower to make triggering a ABN_BEMF fault not require as much of a change in generated BEMF.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Prodigy 140 points

    Hi Joshua,

    Thanks a lot for your analysis.

    2.

    Joshua Horlander Cruz said:

    Software lock takes the measured phase current output by the MCF8316C's internal Current Sense Amplifier (CSA), passes it through an ADC, and uses software to determine if the phase current has exceeded the threshold set by LOCK_ILIMIT.

    Hardware lock takes the measured phase current output by the MCF8316C's internal CSA and uses a comparator to determine if the phase current has exceeded the threshold set by HW_LOCK_ILIMIT. This detection method will have less delay for detection than the Software method.

    So the software lock and hardware lock are both used for the phase current monitor, and the harware lock is faster than the software lock. So why do we use the software lock? It seems that the hardware lock could satisfy the need in some way.

    3(2)

    Joshua Horlander Cruz said:
    Can you check if the setting of SPEED_LOOP_DIS and CLOSED_LOOP_DIS?

    They are both set to 0, i.e, speed loop and closed loop are enabled. Do you mean setting them to 1, and disable speed loop and closed loop?

    Joshua Horlander Cruz said:
    For the ABN_BEMF fault, setting ABNORMAL_BEMF_THR to 70% sets the greatest threshold for allowable BEMF difference. You can try setting this threshold lower to make triggering a ABN_BEMF fault not require as much of a change in generated BEMF.

    I changed ABNORMAL_BEMF_THR to the minimum value 40%. And I found that ABN_BEMF fault seemed to be ralted with I2C Speed Command Percentage, the motor rotor were all held to stationary state by manual:

    Percent

    Fault

    20

    CONTROLLER_FAULT, ABN_BEMF, MTR_LCK

    30

    CONTROLLER_FAULT, LOCK_LIMIT

    50

    CONTROLLER_FAULT, LOCK_LIMIT

    What's the reason?

    In the datasheet section 7.3.22.13.2, " This estimated back-EMF is compared against the expected back-EMF calculated using the estimated speed and the BEMF constant." What is "the estimated speed"? Is it the speed value set by I2C Speed Command Percentage?

    4.In a NOT closed-loop stage such as open-loop stage, LOCK_ILIMIT is the only wat to detect a stall condition, right? And is ABN_BEMF still valid for speed abnormal detection?

    Thanks,

    Alex

  • 0 in reply to Alex Wang
    TI__Mastermind 26610 points

    Hi Alex,

    Alex Wang said:
    So the software lock and hardware lock are both used for the phase current monitor, and the harware lock is faster than the software lock. So why do we use the software lock? It seems that the hardware lock could satisfy the need in some way.

    With two settings you can set different current detection values if desired. only HW_LOCK_ILIMIT or LOCK_ILIMIT maybe sufficient but using both will offer redundant protection increasing protection.

    Alex Wang said:
    They are both set to 0, i.e, speed loop and closed loop are enabled. Do you mean setting them to 1, and disable speed loop and closed loop?

    Correct, I was asking to check if both settings were set to 1 which  would mean both the speed and closed loop are set to disabled.

    Alex Wang said:
    In the datasheet section 7.3.22.13.2, " This estimated back-EMF is compared against the expected back-EMF calculated using the estimated speed and the BEMF constant." What is "the estimated speed"? Is it the speed value set by I2C Speed Command Percentage?

    Estimated speed refers to the algorithms current reference speed which can be read in register 0x5CC (SPEED_REF_CLOSED_LOOP).

    Alex Wang said:
    4.In a NOT closed-loop stage such as open-loop stage, LOCK_ILIMIT is the only wat to detect a stall condition, right? And is ABN_BEMF still valid for speed abnormal detection?
    Alex Wang said:
    I changed ABNORMAL_BEMF_THR to the minimum value 40%. And I found that ABN_BEMF fault seemed to be ralted with I2C Speed Command Percentage, the motor rotor were all held to stationary state by manual:

    Please allow me some time to look deeper into ABN_BEMF and ABN_SPEED faults. I will aim to get back to you by 7/24.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Prodigy 140 points

    Hi Joshua,

    Joshua Horlander Cruz said:
    Please allow me some time to look deeper into ABN_BEMF and ABN_SPEED faults. I will aim to get back to you by 7/24.

    OK, get it.

    Thanks,

    Alex