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AFE4300 EVM: DC bias using INA in receive BCM network?

Mathews John
Prodigy 105 points
Other Parts Discussed in Thread: AFE4300

Hey, 

I was going through the schematic for the evaluation module and noticed that a DC bias (~1.7V) is added to the signals when using the INA (U5). I am assuming that this was done so as to bring the signal upto a range well within the ADCs input range in the cases of measuring sub 10Ohm impedances accurately. However, there is no such bias added when the INA is bypassed. I wanted to know why this was so.

Without the INA is it safe to assume that the device is less reliable at very low impedances? I really wanted to figure out the evaluation module better before I started tinkering.


Thank you

  • 0
    TI__Genius 12575 points
    Hi Mathews,

    I am assuming you are talking about VCM signal.
    The INAs in the EVM are configured as the buffers and the VCM signal sets the common mode of the buffers. Since AEF4300 expects the VSENSE signal with some common mode voltage , these ( i.e. VCM) are used.
    Now if you bypass the INA, the common mode is set by the excitation amp itself so there no needs of VCM.
    AFE4300 can be used without INA reliably but for the very low impedance its good to have INA and in that case you need the VCM signal.

    Regards,
    Prabin