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DRV8704: Can the DRV8704 be used to drive a Peliter device for heating and cooling.

Kevin Oscroft
Prodigy 60 points
Part Number: DRV8704
Other Parts Discussed in Thread: DRV8412,

The ideal application would involve driving the AIN1 and AIN2 in anti-phase with 50% duty cycle representing zero current. The two outputs would sit at mid-rail. As the duty cycle is changed one output would move up and the other down. The datasheet for the chip and Eval board do not show feeding PWM into the two inputs at the same time to be an option. Is this possible?

  • 0
    TI__Guru** 114905 points
    Hi Kevin,

    Feeding a single PWM into the two inputs is not possible. The outputs will transition from Hi-Z to both low doing this.

    You need two PWM outputs. Each one is connected to an input. This will allow you to drive the Peltier as described above.
  • 0 in reply to Rick Duncan
    Prodigy 60 points

    Hi Rick,

    Maybe I did not describe the set-up I was thinking of very well. There would be two PWM sources, connected to separate inputs. They originate from the same source, but one would have been passed through an inverter. The idea is that with both PWMs at 50%, but 180 deg out of phase. the outputs should both sit at mid-rail. If the duty cycle of the source was changed to 40%, the inverted version would go to 60%.

    Would one output go to 60% of rail and the other to 40% of rail, thus creating a drive voltage. If this worked we could drive forward and reverse (Heat vs Cool) simply by moving the duty cycle of the source either side of the 50%.

  • 0 in reply to Kevin Oscroft
    TI__Guru** 114905 points
    Hi Kevin,

    From the input point of view you can do as you described (having one PWM and inverting one path).

    The outputs require a little filtering to create the voltages you desire. Please refer to figure 17 of the DRV8412 datasheet. The DRV8412 is shown operating in parallel, but the DRV8704 does not to since external FETs are used.
  • 0 in reply to Rick Duncan
    Prodigy 60 points

    Thank you for your help. I have tried the DRV8412 and it works well (with inductors and capacitor filtering) but losses from internal FETs RDSon is too high. Hopefully the DRV8704 with external low RDSon FETs will be a better solution.

  • 0 in reply to Kevin Oscroft
    TI__Guru** 114905 points
    Hi Kevin,

    Good luck with the DRV8704. Let us know if you further questions.