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DRV8871: How to measure load current of DRV8871

Huang Stone
Prodigy 20 points
Part Number: DRV8871
Other Parts Discussed in Thread: DRV8210EVM, DRV8251A

The way to measure load current:   we insert high precision 1 ohm resistor between PGND pin and PCB ground。Then we amplifier the voltage signal across 1 ohm res and measure it by ADC.

The issue is that there still have several mA even if no load connected. The "extra current"  will change according to VM and is very similar with IVM. 

We have below question:

1. Does IVM flow into PGND?

2. Do you have other method to measure load current ?

3. Will you recommend other part if IVM flow into PGND for DRV8871? 

  • 0
    TI__Mastermind 37683 points

    Hi Huang,

    Huang Stone said:
    2. Do you have other method to measure load current ?

    There will be some leakage current from VM to GND but I'm surprised is in the mA range. Can you provide more details as to how you are measuring this current. Is the H-bridge in High-Z state or not? What tool are you using for measuring the current (multimeter, current probe)?

    Huang Stone said:
    2. Do you have other method to measure load current ?

    Your solution is an acceptable way of measuring the current. We have done this method in some of our evaluation modules. You can look at the DRV8210EVM as an example.

    One thing you have to keep in mind with this solution is that the voltage drop across the resistor should not be greater than 0.3V. The reason is because all of the circuits on the IC are referenced to the device GND. If the device pin GND is above 0.3V with respect to the PCB GND, there can be potential issues.

    Huang Stone said:
    3. Will you recommend other part if IVM flow into PGND for DRV8871? 

    If you need to sense current, the DRV8251A would be a good choice. This device comes with an integrated current sense amplifier so there will be no need for splitting the device and PCB GNDs. You'll only need a small resistor on the IPROPI pin.