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LM2621: Cf1 resistor value

prachi p
Intellectual 300 points
Part Number: LM2621

Hi,

It is recommended to use a 39-pF capacitor (CF1) connected across RF1 helps in feeding back most of the AC ripple at VOUT to the FB pin. However, in the SEPIC converter configuration (figure 18), a 33pF capacitor is used. 

Please tell me why a different value is required to be used for a SEPIC converter.

Regards,

Prachi 

  • 0
    TI__Guru 73570 points
    There is not a hard criteria for CF1 to be an exact value. As you read, the purpose is to help feed the AC ripples to FB, and 33pF and 39pF should not cause much differences, and both should work. If you insist on getting the exact value, simply use 39pF and consider 33pF as a typo. You can see reference designators are not always matching between the datasheet schematic and the related BOM.