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DRV8305: Is there switching mode we must not control?

Takao Yamamoto
Genius 4135 points
Part Number: DRV8305

Dear all,

I think to drive this device with 6-PWM mode.

Is there switching mode that I must not control?

I concern about charging current to VCPH-PVDD cap and VCP_LSD-GND cap.

I concern about following case...high side FET is ON continuously, high/low side FET is OFF continuously, electric charge disappear with constant current control, and inrush current flow when low side FET turn ON with CP2H-CP2L and CP1H-CP1L electric charge disappeared.

Best regards,

  • 0
    TI__Expert 4435 points
    Hi Yamamoto-san,

    Would you kindly send a diagram explaining concern case. I apologize for not following your explanation. Thank you.
  • 0 in reply to Luis Riveros
    Genius 4135 points

    Hi Riveros-san,

    Thank you for your reply.

    I concern and wonder if there may be bad control mode to activate DRV8305 abnormaly.

    I think that we should take care the relationship between FET motion and charging current of charge pump capacitances.

    For example, I think that there may be some problem like attachment file.

    DRV8305question.pdf

    If there are some precautions we should think, please teach me.

    Or... If there are no precautions, please inform me.

    Best regards,

  • 0 in reply to Takao Yamamoto
    TI__Expert 4650 points

    Hi Yamamoto-san,

    Q1:  VCPH-PVDD electric charge can maintain its capacitance under following situation?

    1. the case that high side FET is ON continuously
      1. The DRV8305 will support 100% duty cycle operation because of our charge pump architecture.  There is no need to refresh any external bootstrap capacitor, so there is no issue leaving the external high-side MOSFET ON.
    2. high/low side FET is ON continuously
      1. Same comment as above, no issue with this operation.  Charge pump can support leaving both these MOSFETs on.

    Q2: Does inrush current flow under following situation?

    1. In this scenario that both capacitance are zero, the charge pump would flag a VCPH_UVLO2 and shut down the charge pump and gate driver.  This would happen as soon as the VCPH voltage was detected to be below the VCPH_UVLO2 threshold, not when the low-side MOSFET is turned on.