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MCF8316A: EVM used to configure component off EVM board?

Joe Carlson
Prodigy 80 points
Part Number: MCF8316A

Tool/software:

I am trying to use PN: MCF8316A to drive a BLDC motor at a speed of 75,000 rpm. First question - is this achievable based on allowed switching speeds of the FETs?

Second, I don't want to go through all the trouble of building out custom software / firmware if there is an easier way. I see that the GUI for the EVM board has a nice / easy interface to make all the configurations needed. Is it possible to use the GUI to configure a MCF8316A that is not on the EVM board? I am trying to design a first proof of concept device which requires a smaller form factor.

Thanks!

Joe Carlson

  • 0
    TI__Mastermind 24740 points

    Hi Joe,

    Joe Carlson said:
    I am trying to use PN: MCF8316A to drive a BLDC motor at a speed of 75,000 rpm. First question - is this achievable based on allowed switching speeds of the FETs?

    Can you share you motors datasheet? The MCF8316A can reliably spin a motor up to 1500 Hz although depending on the motor's parameters we have been able to spin motors at higher speeds.

    Joe Carlson said:
    Is it possible to use the GUI to configure a MCF8316A that is not on the EVM board?

    It is possible to use the GUI to configure a MCF8316A that is not on the EVM. To do this you will need to connect the SCL, SDA, and AND pins of the external MCF8316A to the MCU_SCL, MSU_SDA, and AGND pins on the left side of the J6 header on the MCF8316AEVM.

    Alternatively, you can use the code example in the Program MCx BLDC motor driver through I2C using MSP430 LaunchPad FAQ to program a register configuration made using the GUI+EVM into a MCF8316A device not on an EVM.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Prodigy 80 points

    https://www.maxongroup.us/medias/sys_master/root/8882127274014/EN-21-190.pdf

    Hoping this link works to take you to the motor datasheet.

    That is great news about the off-board EVM! To be clear, once the GUI is used to configure the off-board MCF8316A there is no longer a need to have the connection?

    Lastly, what should I set the analog voltage to be if I want to run the motor at 75,000 rpm which is the same as 1,250 revs / second (aka 1,250 Hz)?

  • +1 in reply to Joe Carlson
    TI__Mastermind 24740 points

    Hi Joe,

    The link worked, I am able to access the motor datasheet. The MCF8316A can drive the motor at 75,000 rpm. Using the information in the motor datasheet and the equation below, the electrical frequency for 75,000 rpm is 1250 Hz which the MCF8316A can drive. 

    Joe Carlson said:
    That is great news about the off-board EVM! To be clear, once the GUI is used to configure the off-board MCF8316A there is no longer a need to have the connection?

    Once you have the configuration set in the GUI that works, you can write this register configuration into the MCF8316A's EEPROM which will be loaded into the registers at power up. Once the configuration is written into EEPROM, the MCF8316A will not require a connection to an MCU to drive a motor.

    Joe Carlson said:
    what should I set the analog voltage to be if I want to run the motor at 75,000 rpm which is the same as 1,250 revs / second (aka 1,250 Hz)?

    This depends on what is set in MAX_SPEED. Assuming MAX_SPEED is set to 1250 Hz, then a voltage of >3.05V will run the motor at the desired speed of 75,000 RPM. Please see section 7.3.8.1 of the MCF8316A datasheet for more information.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Prodigy 80 points

    Thanks Joshua!

    A couple more questions for you as I am peeling the layers of the onion of the design:

    1) How accurately (in degrees) can the MCF8316A brake the motor? If I were to have a home position where the motor should park / brake every time is that achievable with this motor controller IC or do I need an absolute encoder?

    2) If I don't need the buck regulator what should I should do with SW_BK and FB_BK pins? 

  • 0 in reply to Joe Carlson
    TI__Mastermind 24740 points

    Hi Joe,

    Joe Carlson said:
    1) How accurately (in degrees) can the MCF8316A brake the motor? If I were to have a home position where the motor should park / brake every time is that achievable with this motor controller IC or do I need an absolute encoder?

    Let me check on the accuracy that can be expected from the Align break feature. I will aim to get back with you by Friday.

    Joe Carlson said:
    2) If I don't need the buck regulator what should I should do with SW_BK and FB_BK pins? 

    If you are not using the buck, set BUCK_DIS to 1b and setting BUCK_SEL to 00b and this can be set in the devices EEPROM to load these settings at startup. Once these are set, you can leave the SW_BK pin floating and connect the FB_BK pin to AVDD, this does lead to additional power losses. For more information please take a look at question 7 of the Common MCx Schematic and Layout FAQ.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    TI__Mastermind 24740 points

    Hi Joe,

    We recommend using an absolute encoder for stopping a motor in a home position. While the align break can be accurate to stop the motor at a given vector, the motor could stop at two different positions depending on its position when the align break is applied. 

    Regards,

    Joshua