SM72485 Datasheet, PDF (12/16 Pages) National Semiconductor (TI) – SolarMagic 100V, 150 mA Constant On-Time Buck Switching Regulator

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FIGURE 5. Efficiency vs. Load Current and V_IN
FIGURE 6. Efficiency vs. V_IN
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LOW OUTPUT RIPPLE CONFIGURATIONS
For applications where low output ripple is required, the fol-
lowing options can be used to reduce or nearly eliminate the
ripple.
a) Reduced ripple configuration: In Figure 7, Cff is added
across R_FB2 to AC-couple the ripple at V_OUT directly to the FB
pin. This allows the ripple at V_OUT to be reduced to a minimum
of 25 mVp-p by reducing R3, since the ripple at V_OUT is not
attenuated by the feedback resistors. The minimum value for
Cff is determined from:
where t_ON(max) is the maximum on-time, which occurs at V_IN
(min)^{. The next larger standard value capacitor should be used}
for Cff.
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