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MCT8316A: Regarding PWM_MODUL

Daisuke Higa
Genius 3645 points
Part Number: MCT8316A

Hi support team.

My customer asked us regarding PWM_MODUL settings.

Q1:

The setting value 3h for PWM_MODUL is N/A.

However, it is configurable.

The motor is rotating.

Please tell us what this setting means and when to use it.

Q2:

When the speed command is low, it seems to be fixed at High side modulation.

PWM_MODUL settings are not reflected at low speeds.

Example: Set PWM_MODUL=2h(Mixed modulation)

-> When SPD_CMD=10%, it operates as High side modulation.

Is the above operation automatically performed inside the device?

Also, why is this behavior happening?

Best regards,

Higa

  • 0
    TI__Genius 13460 points

    Hi Higa,

    The PWM_MODUL selection N/A or Not Applicable is not intended to be selected as the PWM modulation setting. 

    For Q2:

    Does the device still seem to operate in High Side Modulation if set to low side modulation? If it does please try and program the desired register setting to EEPROM and power cycle the device to verify that the device is using the correct register settings and recheck the behavior.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Genius 3645 points

    Hi Joshua-san

    Thank you for answering.

    You said;

    "The PWM_MODUL selection N/A or Not Applicable is not intended to be selected as the PWM modulation setting. "

    Q : So, what is the intended purpose of this setting "N/A"?

    Regarding the answer for Q2;

    I will confirm to my customer. 

    Best regards,

    Higa

  • 0 in reply to Daisuke Higa
    TI__Genius 13460 points

    Hi Higa,

    Daisuke Higa said:
    what is the intended purpose of this setting "N/A"?

    I will need to look into this. I will get back with you by Friday.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Genius 3645 points

    Hi Joshua-san

    You said;

     "Does the device still seem to operate in High Side Modulation if set to low side modulation? "

    -> Yes.

    "If it does please try and program the desired register setting to EEPROM and power cycle the device to verify that the device is using the correct register settings and recheck the behavior."

    ->They wrote the register settings to the EEPROM and checked the operation, but there was no change.
    The PWM_MODUL setting is Mixed Modulation, but at low speed settings with SPD_CMD it becomes Highside Modulation.
    Also, as the speed increases, it automatically switches to Mixed Modulation.

    Best regards,

    Higa

  • 0 in reply to Daisuke Higa
    TI__Genius 13460 points

    Hi Higa-san,

    I will also look into the PWM modulation at low speeds. I will get back with you by Friday.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Genius 3645 points

    Hi Joshua-san

    Do you have any update?

    Best regards,

    Higa

  • 0 in reply to Daisuke Higa
    TI__Genius 13460 points

    Hello Higa-san,

    Daisuke Higa said:
    what is the intended purpose of this setting "N/A"?

    The intended purpose is to not be selected and is an extra bit combination (11b) that was left over since there are 4 possible bit combinations but only three PWM_MODUL settings. If this setting is selected the default value for the register will be used. In the case of PWM_MODUL the 0b setting or high-side modulation will be selected.

    Joshua Horlander Cruz said:
    Does the device still seem to operate in High Side Modulation if set to low side modulation?

    I am still waiting for a response from our firmware team on why the PWM modulation is using high-side modulation at low speeds despite which PWM_MODUL setting is used. I will get back with you by Wednesday on this.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Genius 3645 points

    HI Joshua-san

    Thank you for confirming.

    Thank you for confirming.
    However, in reality, we have confirmed that when N/A is selected, actions other than the three selections occur.
    The waveform is shown below.
    Hasn't the device of the latest production lot been changed so that "N/A" cannot be selected? The EVM I am currently using is a device that has just been mass-produced.

    N/A is selected.

    Highside Modulation is selected.

    Best regards,

    Higa

  • +1 in reply to Daisuke Higa
    TI__Genius 13460 points

    Hi Higa-san,

    It seems I was mistaken about how inputting 11b into PWM_MODUL will affect the devices operation. We do not prevent a user from writing 11b to the PWM_MODUL bit field in the MCT8316A but we do not recommend writing 11b to PWM_MODUL. We will look into preventing the GUI from allowing the user to select N/A options.

    At lower speeds the PWM modulation will always be set to High-Side Modulation as you saw. High-Side Modulation is used since it was determined that it provides the highest BEMF detection accuracy at lower speeds.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Genius 3645 points

    Hi support team

    Thank you for confirming.

    I understand well.

    Thanks.

    Regards,

    Higa