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LM22670 feedback path

Shang Wu18
Intellectual 260 points

I'm using the recommended configuration on the datasheet, however, would like to keep the switching noise low. I'm adding an additional LC filter stage at the output. Should I tie the feedback resistor (R_FBT) to the input of this LC filter or the output of it? I think tying to the output of it makes more sense, but need to confirm with you. Thanks.

  • 0
    TI__Guru 57555 points

    Connecting the FB to the output of the post filter will improve the load regulation by compensating for the resistance of L1; as you surmised.

    Unfortunately, this will also introduce a second order pole into the feedback loop and cause the regulator to be come unstable. 

    If your post filter corner frequency is more than 100 or 200kHz, then it might be OK.  But I think the safest thing to do would be to connect the FB to the input of the filter.