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TPS7A8300 Sense/Feedback Pins and loop Stability with active device in its path

waqar hyder
Intellectual 480 points

Hi

 

We are designing our circuit as shown in the picture below. Our concern is the sense pin path is not DC coupled, but has a op-amp to isolate the 1K resistor that is inserted into its path near the point of load. This was to isolate the load from pick-up noise due to the sense pin trace. (The load and the 1K sense pin resistor in on a different PCB) and the sense pin/output power goes through a board to board interface.


Since the sense pin current is not negligible, the 1K series resistance in its path will disrupt the voltage regulation if we don't insert an active device in the path to isolate it.

 

Our concern is the loop stability of that circuit. Will the regulator output be stable with this circuit ? 

 

 

h the sense pin trace.

In the datasheet the sense pin is shown as DC coupled and directly connected from point of load and then the feedback pin is ac-couple from the sense pin through a 10nF cap. Is any information about the loop stability.  Any app notes for this issue

 

  • 0
    TI__Guru 55940 points
    Hi Waqar,

    This is an unusual application. I am unaware of any application notes related to your question. We will respond shortly.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    TI__Guru 55940 points
    Hi Waqar,

    There are a number of variables in your schematic that could pose a stability problem. In a typical LDO application, inductance is minimized in the feedback loop. As such, the normal sense point would be on the LDO side of FB18.

    I see that you have a ferite bead as well as the opamp. While I have not placed an active component in the feedback loop, if the bandwidth is wide enough, it may be ok. If you would like to pursue this design a prototype board to test stability is highly recommended.

    Very Respectfully,
    Ryan