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DRV10987: Spread spectrum modulation control

Jonathan Ludwig
Prodigy 40 points
Part Number: DRV10987

Hi guys,

i have a question regarding the DRV10987 spread spectrum modulation control functionality.

According to the datasheet, one can set the CONFIG1 Register Bit 15:14 for spread spectrum modulation control as follows:
00: No spread spectrum
01: ±5% dithering
10: ±10% dithering
11: ±15% dithering

For testing, i have attached a current probe into one motor phase, connected it to a spectrum analyzer and captured the following screenshot

  • No SSM -> green trace
  • 15 % dithering -> yellow trace (Similar results can be seen with ±5% dithering and ±10% dithering.)

PWM freq was set to 50 kHz. One can clearly see the peak and its harmonics. However, I would have expected the peaks to more or less disappear and the overall noise level to rise when enabling the SSM.

Any suggestions? Am i doing something wrong? To me, it looks like the PWM frequency is shifted but not increased regarding the bandwidth.

Help is highly appreciated.

Thanks in advance, Jonathan

  • 0
    TI__Intellectual 2600 points
    Jonathan,

    I agree not what I would have expected to see. I would have expected all of the frequencies to be there but with a more rounded shape and lower peak value. Not sure what might be causing the behavior you've observed.

    Could you send me your EEPROM settings (you can just save the config file and send that to me). So that I can review them.

    I'll also try to duplicate the measurement that you're making on my bench.

    Thanks,
    Brian
  • 0 in reply to Brian Schmidt
    Prodigy 40 points

    Hi Brian,

    thanks for the reply!

    The config looks as follows (SSM disabled)

    DRV10987_Fault Reg    0100
    DRV10987_MotorSpeed    0445
    DRV10987_MotorPeriod    03B0
    DRV10987_MotorKt    0026
    DRV10987_MotorCurrent    0000
    DRV10987_IPDPosition / SupplyVoltage    1666
    DRV10987_SpeedCmd / spdCmdBuffer    3232
    DRV10987_AnalogInLvl    0000
    DRV10987_Device ID / Revision ID    0000
    DRV10987_nFaultReg    0000
    DRV10987_SpeedCtrl    8064
    DRV10987_EEPROM Programming1    C0DE
    DRV10987_EEPROM Programming2    0000
    DRV10987_EEPROM Programming3    0000
    DRV10987_EEPROM Programming4    0000
    DRV10987_EEPROM Programming5    1000
    DRV10987_EEPROM Programming6    0000
    DRV10987_InternalTestKey    3A6C
    DRV10987_TestModeEnable    0000
    DRV10987_TestMode1    0000
    DRV10987_TestMode2    0000
    DRV10987_AMux    0000
    DRV10987_Dmux    0000
    DRV10987_ADCMux    0000
    DRV10987_ADCData    0000
    DRV10987_ADC2    0000
    DRV10987_EETEST1    0000
    DRV10987_EETEST2    0000
    DRV10987_EETEST3    0000
    DRV10987_EECTRL    0000
    DRV10987_VREG_TEST1    0000
    DRV10987_IDDQ_TEST1    0000
    DRV10987_DigTest1    0000
    DRV10987_DigTest2    0000
    DRV10987_SCORE0    0000
    DRV10987_SCORE1    0000
    DRV10987_SCORE2    0000
    DRV10987_ADCCorrection1    0000
    DRV10987_CONFIG1    005D
    DRV10987_CONFIG2    1A49
    DRV10987_CONFIG3    0C81
    DRV10987_CONFIG4    43A0
    DRV10987_CONFIG5    3BAF
    DRV10987_CONFIG6    7853
    DRV10987_CONFIG7    046A
    DRV10987_ADCCorrection2    0000
    DRV10987_FaultControl    0000
    DRV10987_TRIM0    864D
    DRV10987_Trim1    4560
    DRV10987_Trim2    4E73
    DRV10987_Trim3    4B4B
    DRV10987_Trim4    4A4B
    DRV10987_Trim5    8342
    DRV10987_Trim6    1111
    DRV10987_DIE_TRACE1    0000
    DRV10987_DIE_TRACE2    0000
    DRV10987_DIE_TRACE3    0000

    Best,

    Jonathan

  • 0 in reply to Jonathan Ludwig
    TI__Intellectual 2600 points

    Jonathan,

    I don't see anything obvious. I'll see if I can duplicate your finding with one of my motors.

    Thanks,

    Brian

  • 0 in reply to Brian Schmidt
    Prodigy 40 points
    Hi Brian,

    any news on that topic? Were you able to reproduce the measurement?

    Best regards!

    Jonathan
  • 0 in reply to Jonathan Ludwig
    TI__Intellectual 2600 points

    Jonathan,

    I've confirmed your results. I don't see any measurable difference when using the spread spectrum features in DRV10987.

    Spread spectrum performance.pdf

    I will report back to the design team, but I don't expect a silicon revision.

    Regards,

    Brian

  • 0 in reply to Brian Schmidt
    Prodigy 40 points

    Hi Brian,

    thanks a lot for the effort, i appreciate it!

    Jonathan