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LM25148: Question regarding isns and Vout compensation network

Ricardo Carballo
Prodigy 40 points
Part Number: LM25148

Tool/software:

Looking at the data sheet example designs for example Figure 9-4 in the datasheet

The isns and V out paths have not compensation network, 

However in certain applications I see resistor added in series and a capacitor across the two paths. 

For example PMP31252 Schematic

what is the purpose of these added components, is there a supporting equation to calculate the values?

What are the benefits and down sides of adding this to the amplifier?  wouldn't the resistor and capacitor cause delays in the response of the circuit?

Are they still to be routed differentially ?

  • 0
    TI__Guru 73015 points

    Hello

    The added components are used to filter the current sense signal.

    It is best to leave a place on the PCB for these components in case they are needed.

    The values shown give good performance and should be used as a first pass design.

    Alternatively, zero Ohm resistors can be used and the capacitor can be DNP until if and when they are needed.

    Those values will not add excessive delay to the loop.

    You will still route differentially.

    Thanks

  • 0 in reply to Frank De Stasi
    Prodigy 40 points

    Thank you Frank,  Are there any equations or a reference document that can help select these values to better degree? Is this then supposed to be a differential low pass filter from the noisier side of the inductor? 

  • 0 in reply to Ricardo Carballo
    TI__Guru 73015 points

    Hello

    Yes, it is basically a differential filter.

    I am not sure we have any specific equations.

    I think the best thing to do is to start with the given values, and they can be adjusted

    on the board later if needed.

    Thanks