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Original question:

INA282: Measurement of voltage and current

INA282: With load current increase, the output of INA282 oscillates in wide range

Vidhya J
Intellectual 400 points
Part Number: INA282


HI Team,

INA282 is used to monitor negative voltage -6.5V in our design. Refer to the snap below.. 

On board measured output voltage of INA282 varies too much at 1.86A. 

Output variation is as shown below (2.808 to 2.935) at 2.3A load. while for lesser load. don't see much variation.

Thanks and Regards,

Vidhya

  • 0
    TI__Mastermind 22905 points

    Vidhya,

    Can you share what's driving the load here? From the oscilloscope, the instability appears to be coming from the load line itself, as the INA282 is simply gaining the differential voltage you are seeing here. Is the load meant to be stable DC, or is it switching in some way?

  • 0 in reply to Carolus Andrews
    Intellectual 400 points

    Hi Carolus Andrews,

    We are using variable resistive load (Rheostat) at output of -6.5V rail.

    Load is not the issue. This oscillation is more evident with >1.86A load. 

    Even for lesser load cases, there are oscillations at INA282 output but it is within limits.

    PFA INA282 output with 1A load varies by 60mV.

    Regards,

    Vidhya

  • 0 in reply to Vidhya J
    TI__Mastermind 22905 points

    Vidhya,

    Am I misunderstanding the scope shot? If I am interpreting the scope shot correctly, the red waveform is the current input to the INA282, and the blue is the output? Can I get a break down of the signals being displayed in the shot?

  • 0 in reply to Carolus Andrews
    Intellectual 400 points

    Carolus,

    Red waveform is the input to INA282.

    Blue is the output of INA282 after a resistor divider

    Regards,

    Vidhya

  • 0 in reply to Vidhya J
    TI__Mastermind 22905 points

    Vidhya, 

    If this is the case, the scope shot demonstrates that the load current is the issue. Whether or not the INA282 is doing something impedance-wise at the inputs to distort the load line is up for debate, but the scope shots clearly show the same oscillation on both the input and output of the device. If these oscillations are present in the differential voltage across the shunt, they are going to be amplified and present in the output of the INA282. This means the problem is stemming from something on the input side of the device, not the output, as the load line current is distorted.  

    Has the customer removed the INA282 from the load line to ensure this is what is causing these oscillations? I'm assuming the expected waveform is simply a DC current? Do they see this behavior correct if they remove the device? Could we see a scope shot of the load current when the device is depopulated?