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Original question:

DRV8703-Q1: Using a different H Bridge Voltage than Controller Supply on PVDD

DRV8703-Q1: VREF Pin floating

Needhu Gunasegaran
Intellectual 2710 points
Part Number: DRV8703-Q1
Other Parts Discussed in Thread: DRV8702-Q1,

Hello Team,

Could you please help answer a customer question?

Is it possible to leave the VREF-Pin floating if the part is operating with Independent PWM Control mode (MODE = 1). Can the application be affected by a floating VREF-Pin in this mode in any way?

In the Datasheet it is said: „If the independent PWM control-interface mode (MODE pin is 1) is selected for operation, the device does not perform PWM current regulation or current chopping.“

http://www.ti.com/lit/ds/symlink/drv8703-q1.pdf?&ts=1589965862072

Thank you very much in advance.

Best Regards,

Needhu

  • 0
    TI__Guru** 114905 points

    Hi Needhu,

    Leaving VREF floating can lead to extra power losses, although minor.

    If VREF is left floating, the output of the comparator may switching internally.

    Since current regulation is disabled, it is recommended to connect VREF to AVDD to avoid this internal switching.

  • 0 in reply to Rick Duncan
    TI__Intellectual 2710 points

    Hello Rick,

    Hope you are well.

    I have a followup question.

    Can the VREF pin also be tied to GND instead of AVDD?

    The set value of the Motor Current would be 0Amps if the internal current regulation is activated unintended (Failure of MCU-Pin ect.).

    To me this appears to be the safer way. Are there any disadvantages?

    Thanks,

    -Needhu

  • 0 in reply to Needhu Gunasegaran
    TI__Guru** 114905 points

    Hi Needhu,

    Please refer to Figure 29 of the datasheet. You can see setting VREF to 0 means the current regulation is effectively always enabled and should begin regulation immediately after the tblank time.

    Connecting VREF to AVDD, plus setting the Av * Risense well below the VREF value disables the internal current regulation.

  • 0 in reply to Rick Duncan
    TI__Intellectual 2710 points

    Hi Rick,

    feedback from customer is as follows,

    in the Datasheet it is said that current regulation is always deactivated if the MODE-Pin is tied high (independent PWM control):

    In our application we’re controlling the DRV completely by PWM (Mode-Pin is tied to high). So the current regulation is not enabled at all.

    Can it have an adverse affect to tie VREF-Pin to GND instead of AVDD with this configuration?

    And fig. 29 of the Datasheet refers to the DRV8702 (were using DRV8703). Was this the figure you meant?

    Thanks,

    Needhu

  • 0 in reply to Needhu Gunasegaran
    TI__Guru** 114905 points

    Hi Needhu,

    If the customer is using Independent mode, VREF can be connected to GND. In general, it is recommend to have a footprint that allows a resistor to AVDD as an option. This will allow evaluation or last minute changes without having to spin the PCB.

    Connecting VREF to GND has no adverse effects other than possibly some additional internal switching at the output of the comparator.

    You are also correct that Figure 29 refers to the DRV8702-Q1, although the section showing the amplifier and comparator is the same for both the DRV8702-Q1 (Figure 29) and the DRV8703-Q1 (Figure 30).