JAJSB11H April 2009 – November 2014 LM25011 , LM25011-Q1
PRODUCTION DATA.
This configuration generates less ripple at VOUT than Option A by the addition of capacitor (Cff) as shown in Figure 23.
Because the output ripple is passed by Cff to the FB pin with little or no attenuation, the R1 value and VOUT ripple can be smaller than in Option A. The minimum value for R1 is calculated from:
where ΔI is the minimum ripple current amplitude, which occurs at minimum VIN, and VRIPPLE is the peak-to-peak ripple voltage injected at the FB pin. The minimum value for Cff is calculated from:
where tON(max) is the maximum on-time (at minimum VIN), and RFB1//RFB2 is the parallel equivalent of the feedback resistors.