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drv8308evm clock frequency mode

Elavarasan Selvaraj
Prodigy 70 points
Other Parts Discussed in Thread: DRV8308EVM

hi,

we are using drv8308evm board with external SPI interface (from STM32F429 controller). SPI communication is working. All control signals like ENB,CLKIN,RST everything is controlled by STM32F429. we are working on Clock frequency mode. after some tuning process (register settings is attached down). , we got smooth running of motor with lock. but expected rpm is not met. required rpm = 3000, clkin = 200Hz, measured rpm = 1800. if i change speed register to 500 with 200Hz clkin, motor is not running smoothly and lock is not coming. If i change clkin = 50 Hz,  speed register is 3000 then also motor is not ruuning and no lock.  

Is it possible to achieve required RPM (400 to 4000) by setting all register to a fixed value and changing only CLKIN dynamically? 

Regards,

Elavarasan S

  • 0
    TI__Mastermind 20985 points

    The SPEED register needs to be set high enough to reach your commanded frequency.  The tuning guide recommends a value of 4000.

    If ever the frequency on the FGSEL input doesn't match the applied frequency to CLKIN, speed control is not in effect.

    Best regards,
    RE

  • 0 in reply to RE
    Prodigy 70 points

    hi,

    thanks for your reply.

    i have few more doubts.

    1) fault register not getting clear even written by 0x0000. anything else need to be done?

    2) i have set speed to 4000, clkin to 400hz. Expected rpm is 6000. but getting only 4000 rpm (with lock) . what might be the issue?

    3) speed is 4000, clkin is 100hz. Expected rpm is 1500. now motor is not running smoothly and not locking. what will be the problem?

    can you help on this issue?

    thanks and regards,

    Elavarasan

  • 0 in reply to Elavarasan Selvaraj
    TI__Mastermind 20985 points

    Please confirm your rotor has 8 magnet poles.

    If you can't spin-up to your commanded frequency, typically you can fix that by increasing SPEED or LOOPGAIN.  SPEED is already 4000.  So try increasing LOOPGAIN, or change AG_SETPT appropriately.  If you're driving a big load, we also want to make sure you're not hitting the current limiter (0.25V / Rsense).

    Best regards,
    RE