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DRV8701: Only using High Side Drive

tom prohaszka77
Prodigy 170 points
Part Number: DRV8701

Can the DRV8701 be used in a high side drive mode only, no low side drive?  So we would drive the high side through motor, while the motor is externally grounded.

  • 0
    TI__Guru 56650 points
    Tom,

    Do you mean your setting is similar as Figure 20. Half-H Bridge Operation Mode?
    DRV8701 can support high side drive on continually. Can you find your solution from table 3 and table 4?
  • 0 in reply to Wang5577
    Prodigy 170 points
    Not exactly, only use the high side fet, not the low side fet. Can i remove the low side fet, or put a large resistor in parallel with the motor?
  • 0 in reply to tom prohaszka77
    TI__Guru 56650 points

    Tom,

    We need to provide a current path for the motor when the high side FET is turned off.
    When the winding current is built up and high side FET is turned off, the voltage across the winding is about deltaV=L delta I / delta t. A large resistor may generate higher loss when the high side FET is on, or only allow a small current to pass it which gives a higher delta I. The high voltage could damage the high side FET. Please add a diode to replace the low side FET to provide a current path when high side FET is turned off.

  • 0 in reply to Wang5577
    Prodigy 170 points
    Is the suggestion to remove resistor and replace with diode in parallel with Motor? Or a TVS between Vbatt and ground, around the fet? If it's a diode, this will allow the DRV8701 to run only a high side FET? Do i need to do anything with the low side pins on the DRV8701?
  • 0 in reply to tom prohaszka77
    TI__Guru 56650 points
    Tom,

    Use Figure 20 as reference, replace the low side FET with a diode.
  • 0 in reply to Wang5577
    Prodigy 170 points
    Hi, can you still assist? I'm using the DRV8701P (Pwm) version. I removed FETS on the GH2/SH2/GL2, and tied the SH2 to ground via 330 resistor per Figure 20. I removed the lowside fet from GL1 also, which leaves me with the floating High Side drive. I added a diode in parallel with a resistor between SH1 and Ground ( low side FET on GL1 is not connected anymore, GL1 is floating). I added a 100K between GH1 and SH1. It sort of works. When operating, my load is activated, but the Gate Drive is dropping out and the fault bit becomes set, until eventually i reach Full On at 100% duty.

    Same goal as before, I just want to use the high side gate drive, nothing else.
  • 0 in reply to tom prohaszka77
    TI__Guru 56650 points
    Tom,


    The datasheet "8.2.1.2.1 External FET Selection" give an equation for the FET's Qg, PWM frequency and gate drive current capability. What is your PWM frequency and the FET's Qg?

    BTW, what resistor is used between SH1 and Ground? Can you remove that resistor since a diode is put between SH1 and Ground.