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Current measurement with DRV8332

Charles Jackel
Expert 1345 points
Other Parts Discussed in Thread: DRV8332, DRV8312

My question is in reference to Figure 13 (Schematic Example) on page 21 of the DRV8312/DRV8332 Datasheet (TI reference SLES256):

What is the voltage and current range for pins GND_A, GND_B, and GND_C ? They are shown in the schematic as connected to op-amp circuits that appear to be used for sending a voltage to the Analog-Digital Converter (ADC) module of a digital signal processor (DSP).

I want to do the same thing in my project. The ADC module input checks for a voltage of 0 (zero) volts, 0 volts <voltage<3 volts, and voltage >3 volts and converts this voltage into a digital value per the ADC datasheet. In order for me to analyse the circuit, I need to know the voltage and current at the GND_A, GND_B and GND_C pins.

  • 0
    TI__Guru 55615 points

    Charles,

    The GND_x pins are internally connected to the low-side FETs of each channel.  The current that flows through each low-side FET flows out through this pin to the board GND.  We recommend a delta of 100mV maximum between these pins and the GND of the system.  This is shown in the datasheet. 

    There really is no current rating for the GND_x pins in particular.  There is a current rating for the phase current and this current flows through the GND_x pin.  This is going to depend on your load.  Once you know the phase current in your application, you can choose a sense resistor that will guarentee a <100mV voltage drop across the resistor.  V = IR in this case.  The sense resistors are typically on the order of 5-10mohms. 

    If you check out one of our kits, DRV8312-C2-kit, you can see the circuit used on the boards. 

  • 0 in reply to Ryan Kehr
    Expert 1345 points

    The motor that will be used in the project is a 3-phase BLDC with a maximum continuous current rating of 4 amps. The winding data for this motor

    show a peak current rating of 32 amps at the rated voltage of 50VDC, but this project will provide 12VDC to the motor.

    For a sense resistor of 10mohms, voltage drop of 100mV, I=10amps. This is well above the motor's max continuous current rating of 4amps.

    So my phase current in this case would be 4amps, correct? This would give me a max voltage of about 42 mV across the sense resistor.