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DRV8301 amplifier

debe
Prodigy 60 points

Hi,

I am measuring DC bus current with single shunt ressistor in BLDC application.

Output of amplifier circuit is measured with uC 12bit ADC in range 0V - 3.3V.

My question would be:

1. (Current design) How is amplifier expected to behave if:

- Vref=0V would be applied to the pin (2V min, 6V max is stated under recommended operating conditions in DS)

- SN would be grounded (also shunt resistor is grounded in this point)

- SP wold be connected point of measuring shunt voltage (in DS not recommended to do so)

- >In theory we would get non-inverting amplifier circuit and output could be from 0 to 3.3V.

If bias must be added (at least Vref_min/2=2V/2=1V), then we can get amplified signal in range of 1V to 3.3V ->2,3V.

2.  If we connect SN and SP vice versa (SP connected to shunt ground, SN to shunt "voltage measuring" point) and add max bias ( we have 5V available for REF input), that would give us span from 0 to 2,5V. It is a little bit more, but still some "unused" area.

What would be the best option to measure dc current with this amp?

Thank you and best regards

  • 0
    TI__Guru 55615 points

    Hello,

    The amplifiers are setup to measure bi-directional current.  In a single shunt BLDC application, the current will be bi-directional and sinusoidal in nature.  You  will want to center the voltage output of the amplifiers at 1.65V (i.e. connect VREF to 3.3V).  

    This is how our DRV8301EVM is configured today.  

  • 0 in reply to Ryan Kehr
    Prodigy 60 points

    Hi,

    I am not using evaluation board DRV8301EVM. Only driver 8301 on our design.

    Single shunt is measuring dc current trough all three pairs of mosfets together (only positive current, current is not flowing back to DC bus). So I do not need bi-directional measurement, I want to measure DC current in as wide area as possible. With BLDC, I meant simple six step comutation pattern (you have mentioned sinusoidal shape), I am not using vector control in this case.

    Best regards.

    debe

     

  • 0 in reply to debe
    TI__Guru 55615 points

    Debe,

    If that is the case and you only have 5V available for VREF, than your case 2 is the best case possible for maximizing the range.  There is no way to get past the divide by 2 internally as it was really meant for bi-directional current measurement.