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DRV8908-Q1: Continues mode usage

Daniel Wang (auto)
Expert 3550 points
Part Number: DRV8908-Q1

Tool/software:

Hello team,

Pls. support with the below questions:

1. According to the description in the datasheet, the free-wheeling configuration is only applicable in PWM Mode. Can it be used in Continues Mode?

2. In the register OP_CTRL_2, are HBx_HS_EN & HBx_LS_EN only applicable in Continues Mode?

3. In the OLD_CTRL_6 register, it describes the VM_Connected load passive open circuit diagnosis. Why is there only VM_Connected load diagnostics, and no GND_connected load? The OLD_CTRL_6 register introduction is very limited in the datasheet, what is the meaning?

Thanks!

BR,

Daniel

  • 0
    TI__Mastermind 24630 points

    Hi Daniel,

    The description of these modes can be a bit confusing in the datasheet. Continuous mode really means that the high and low side FETs are commanded with 100% duty cycle and not tied to one of the PWM internal generators. 

    Daniel Wang (auto) said:
    According to the description in the datasheet, the free-wheeling configuration is only applicable in PWM Mode. Can it be used in Continues Mode?

    In general, yes it really only applies to PWM mode. Free-wheeling should still work in continuous mode but in this mode the FETs will not be switched much if at all so this feature will not make much of a difference if any.

    Daniel Wang (auto) said:
    In the register OP_CTRL_2, are HBx_HS_EN & HBx_LS_EN only applicable in Continues Mode?

     HBx_LS_EN and  HBx_HS_EN are needed with both PWM operation and DC (continuous) operation. When HBx_PWM is 0b (continuous mode) the HS _FET will follow the HBx_LS_EN or  HBx_HS_EN setting. When HBx_PWM is 1 then the bit in one of the PWM_MAP_CTRL_x register needs to be set to map the PWM channel to HBx and PWM_DUTY_CTRL_x register will be used to set the duty cycle. with HBx_PWM set to 1, the FET that is switched will be the HBx_LS_EN or  HBx_HS_EN bit which is set to 1b.

    Daniel Wang (auto) said:
    Why is there only VM_Connected load diagnostics, and no GND_connected load? The OLD_CTRL_6 register introduction is very limited in the datasheet, what is the meaning

    This bit is not required for typical VM connected POLD operation, this bit is for cases where VM is low so the passive OLD current needs to be larger to properly detect an open condition. for more information on passive OLD please refer to section 8.3.3.5.3. The image below and table 9 in the datasheet provide information on using the passive OLD function.

    Regards,

    Joshua