KB3440EMS datasheet(11/20 Pages) KINGBOR

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SOFT-START

The soft-start function is combined with shutdown. When

the SHDN/SS pin is brought above typically 1V, the IC is

enabled but the EA duty cycle is clamped from the VC pin.

COMPONENT SELECTION

Figure 5. Soft-Start Circuitry

–

VIN

ERROR AMP

1.22V

µA

CP1

VOUT

SHDN/SS

CSS

ENABLE SIGNAL

RSS

SOFT-START

CLAMP

TO PWM

COMPARATORS

CHIP

ENABLE

–

VCI

Inductor Selection

The high frequency operation of the kB3440 allows the

use of small surface mount inductors. The inductor cur-

rent ripple is typically set to 20% to 40% of the maximum

inductor current. For a given ripple the inductance terms

are given as follows:

f I

Ripple V

f I

Ripple V

IN MIN

OUT

IN MIN

OUT MAX

OUT

IN MAX

OUT

OUT MAX

IN MAX

()

•–

••

•

•–

••

•

where f = operating frequency, MHz

A detailed diagram of this function is shown in Figure 5.

The components RSS and CSS provide a slow ramping

voltage on the SHDN/SS pin to provide a soft-start

function.

Figure 6. Recommended Component Placement. Traces Carrying

High Current are Direct. Trace Area at FB and VC Pins are Kept

Low. Lead Length to Battery Should be Kept Short

GND

kB3440

MULTIPLE

VIAS

SHDN/SS

VIN

VOUT

MODE/SYNC

SW1

GND

SW2

VIN

VOUT

kB3440

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