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DRV8307: Use externally Gate-Driver for Low Rdson MOSFET

Artur Bleich
Prodigy 50 points
Part Number: DRV8307
Other Parts Discussed in Thread: DRV832X, DRV8711, TIDA-01227

Hi,

I would use a low Rdson MOSFET Type (<2mOhm) with a Gate Charge of 120nC. For fast switching I need a Gate Current of 1A...2A. Regrettably I only found in the Datasheet the information "30-mA Gate-Drive Current to 6 N-Channel MOSFETs". So I think the DRV8307 can not do it. But I would like use the advantages of it.

Now my idea was to use the DRV8307 in a combination with additionally extern MOSFET-Driver.

Is this Idea usable relating to Delaytime?

Another Problem is the Charge Pump. The High Side Gate Signals (UHSG, VHSG, WHSG) are 10V about the Supply Voltage, in my Case 24V+10V. But my externally Gate-Driver dont tolerate Inputsignals of 34V. My idea to slove this Problem was an simply  voltage divider with Resistors.

Does this make sense or is there another way to bypass the charge pump?

Thanks,

Artur

  • 0
    TI__Guru** 114905 points
    Hi Artur,

    Have you looked at the DRV8320H device?

    Using 1x PWM and setting the IDRIVE pin may meet your needs.
  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Hi Rick,

    Thanks for the fast answer.
    The DRV832x Family is a good solution.

    But my applications need partly 2A...2,5A source Current. The DRV832x have only 2A Sink but 1A Source Current.
    If it's not possible with the DRV8307, I'd use the DRV8307.

    But is it worth a try with the DRV8307 and an externally Gate-Driver or is it a very bad idea?

  • 0 in reply to Artur Bleich
    TI__Guru** 114905 points
    Hi Artur,

    It may be possible to do as you desire, but there are protection features that have to be disabled. The VDS is one of them.
    Another item to consider is many external drivers do not have a charge pump. This will limit the duty cycle to less than 100%.
    The additional circuitry can increase complexity and cost.

    If you want to consider this path, please take a look at the following design for concepts:

    www.ti.com/.../TIDA-01227

    The translators and feedback block of the schematic show how the VDS feature was disabled on the DRV8711. A similar concept can be used for the DRV8307.
  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Hi Rick,

    thank you very much again.

    I have study the Datasheets and came to the following conclusion:

    Because the Supply Voltage of the DRV8307 and the BLDC Motor are the same and thus also the VDS. I think therfore it is not necessary to "disable" the VDS protection feature like the TIDA-01227 Datasheet. There needed a Motor Voltage up to 70V.

    But at next my misgiving was for the timing of the Hallsensor evaluation by the delays from the second Driver.
    An estimate calculation has resulted that an 8 Pole BLDC Motor needs round about 500µs for one cycle of operation from the Fullbridge.  (1/8 turn)
    On the other hand, a delay from the driver is only 250ns. I think thats is comparatively not a great delay. And shouldn't cause any problems.

    Can my two proposals be confirmed?

  • 0 in reply to Artur Bleich
    TI__Guru** 114905 points
    Hi Artur,

    I do not understand your statement "There needed a Motor Voltage up to 70V". Can you explain?
  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Hi Rick,

    sure I try it.

    I'm referring to: www.ti.com/.../tiducr6a.pdf

    Page 2: System configured for 70-V operation; absolute maximum of the DRV8711 is 60 V, recommended maximum is 52 V
    I understand that the application should supply the Motor/Bridge (VM) whith up to 70V but the DRV8711 can only 52V. So I'm not allowed to connect the AOUTX and BOUTX -Monitoring Pins of the DRV8711 whith 70V from the Half Bridges (Page 10). Thats the reson of the "disabeling" from the VDS protection (Page 11).

    Is it right?

    But in my application with the DRV8703 I have the same Voltage on the Bridge (VM) and the supply of the DRV. So I think here it is not necessary to disable the VDS protection. It is only needed connect normaly the middle of the Half bridge at the monitoring Pins.

  • 0 in reply to Artur Bleich
    TI__Guru** 114905 points
    Hi Artur,

    You are correct. The reason the VDS of the DRV8711 was disabled was because of the difference in device voltage and bridge voltage.

    You should be aware of the possible need to disable the VDS in case you run into a similar situation. The configuration you are suggesting has not been evaluated on the DRV8307.
  • 0 in reply to Rick Duncan
    Prodigy 50 points
    Okay Rick, Thanks a lot!
    I try it and give a feedback.