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INA821: Input Bias Current Return Path

Brian Konopka
Prodigy 40 points

Part Number: INA821
Other Parts Discussed in Thread: TINA-TI

Tool/software:

If using the INA821 with a 5k Ohm strain gauge bridge (10V excitation with 0V reference), is providing a path for the input bias current still required as shown in Figure 68 of the datasheet?

  • +1
    TI__Intellectual 1200 points

    Hi Brian,

    Are you using the strain gauge bridge similar to the one below? If so, then that sufficiently provides return path for the bias current. Specifically, there must be a DC return path, which is provided by the direct connection to the bridge.



    You can actually use TINA-TI to simulate this. Below are two examples, the top with a DC return path, and the bottom without a DC return path. As you can see, the bias current of the bottom INA821 charges the input capacitors C1 and C2, forcing the output to saturate to -13V. The top INA821 does not have this issue, and shows a linear output of 200mV.

    Let me know if you have any other questions, or if you have a different design than the one I provided.

    Best Regards,

    Taylor Allan