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DRV8301: Unidirectional current sensing - remove offset from integrated shunt amplifier

asd asd3
Prodigy 10 points
Part Number: DRV8301
Other Parts Discussed in Thread: DRV8323

Hello,

I am designing a trapezoidal BLDC driver and I am going to have only 1 current sense reistor.

All 3 source legs of lower mosfet are connected together and connected to shunt resistor. Other leg of shunt is connected to ground.

This gives me unidirectional current sensing.

Integrated shunt amplifier wants to set Vref/2 offset. Can I short Vref pin to ground so I don't have that offset?

Also my ADC has max 3.3V input, should I have some protection (does integrated amplifier swing all way to AVDD=6V)?

Best Regards

  • 0
    TI__Mastermind 18900 points

    Hello asd asd3,

    Remember, the current sense amplifier (CSA) is in a differential amp configuration so the output is inverting. If you ground the reference, SNx will always be bigger than SPx which means the Vo tries to go negative but hits the GND rail supplying which results in your output always equals 0V (unless SNx - SPx is negative, which result in negative current flow). See the diagram and equation below.

    If we had resdesigned this device, like we did with the DRV8323, we would have added an option to bypass the VREF circuit, so the VREF/2 turns into VREF and the user could use the same voltage rail on VREF as their ADC (which is the preferred way to do it, to eliminate differential noise between the two devices).

    Also, yes, the output will swing to 6V because the AVDD is powering the CSA. So you will need some sort of diode to protect against voltage going higher than that.

    Best,

    -Cole