OUT

IN

OUT

IN

HYST

IN

V

(V

V

) ESR

F

V

(V

L) (V

delay ESR)

-

´

=

´

´ a ´

+

´

´

LM3485

www.ti.com

SNVS178H – JANUARY 2002 – REVISED DECEMBER 2015

Feature Description (continued)

The LM3485 operates in discontinuous conduction mode at light load current or continuous conduction mode at

heavy load current. In discontinuous conduction mode, current through the inductor starts at zero and ramps up

to the peak, then ramps down to zero. Next cycle starts when the FB voltage reaches the internal voltage. Until

then, the inductor current remains zero. Operating frequency is lower and switching losses reduce. In continuous

conduction mode, current always flows through the inductor and never ramps down to zero.

(1)

Figure 22. Hysteretic Window

(2)

(3)

series resistance (ESR) of output capacitor, and the delay. It can be approximately calculated using Equation 4:

where

•

( R1 + R2 ) / R2

•

delay: It includes the LM3485 propagation delay time and the PFET delay time

(4)

The propagation delay is 90-ns typically (see Figure 23).

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