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LM3478: Cfilt placements differ in Webench SEPIC vs Boost design schematic - should it?

Part Number: LM3478

While playing around with design parameters for a LM3478 design, I noticed that Webench's SEPIC schematic and Boost schematic differ in the placement of Cfilt for monitoring Vsense at the Isense pin.

Boost:

SEPIC:

Note that Rfilt and Cfilt are designated the same in both designs, but in the SEPIC Cfilt is parallel to Rsense and precedes Rfilt.

From the perspective of just filtering the sense signal, the configuration in the boost design makes more sense, whereas in the SEPIC design, it will actually change the switching output? 

Are the respective designs actually correct? 

  • Hi Joseph,

    Thanks for pointing this out.

    I agree that there might be a different impact on the regulation based on the placement of the resistor.
    The placement in BOOST topology is the recommended filter implementation.

    An additional resistor directly at the Isense pin will impact the internal slope compensation.

    I will get in touch with our Webench design team to fix this so there is no confusion anymore.
    Thanks and best regards,
    Niklas