Recommended External Components

OUTPUT CAPACITOR, C

OUT

The output capacitor C

the output ripple voltage. In general, the higher the value of

C

ramic capacitors with low ESR are the best choice. At the

lighter loads, the low ESR ceramics offer a much lower V

OUT

ripple that the higher ESR tantalums of the same value. At

the higher loads, the ceramics offer a slightly lower V

OUT

ripple magnitude than the tantalums of the same value.

However, the dv/dt of the V

much lower that the tantalums under all load conditions.

Capacitor voltage rating must be sufficient, 25V or greater is

recommended. Examples of suitable capacitors are: TDK

C3216X5R1E475K,

Panasonic

ECJ3YB1E475K,

ECJMFB1E475K and ECJ4YB1E475K.

Some ceramic capacitors, especially those in small

packages, exhibit a strong capacitance reduction with

the increased applied voltage (DC bias effect). The ca-

pacitance value can fall below half of the nominal ca-

pacitance. Too low output capacitance can make the

boost converter unstable. Output capacitors DC bias

effect should be better than –50% at 18V.

INPUT CAPACITOR, C

IN

The input capacitor C

input ripple voltage and to a lesser degree the V

higher value C

age rating must be sufficient, 10V or greater is recom-

mended.

OUTPUT DIODE, D

1

A schottky diode should be used for the output diode. Peak

repetitive current should be greater than inductor peak cur-

rent (800mA) to ensure reliable operation. Schottky diodes

with a low forward drop and fast switching speeds are ideal

for increasing efficiency in portable applications. Choose a

reverse breakdown voltage of the schottky diode signifi-

cantly larger (~30V) than the output voltage. Do not use

ordinary rectifier diodes, since slow switching speeds and

long recovery times cause the efficiency and the load regu-

lation to suffer. Example of suitable diode is: Central Semi-

conductor CMMSH1-40.

EMI FILTER COMPONENTS C

EMI filter (R

suppress EMI caused by fast switching. These components

should be as near as possible to the SW pin to ensure

reliable operation. 50V or greater voltage rating is recom-

mended for capacitor.

INDUCTOR, L

1

A 10uH shielded inductor is suggested for LP3958 boost

converter. The inductor should have a saturation current

rating higher than the rms current it will experience during

circuit operation (600mA). Less than 300m

Ω ESR is sug-

gested for high efficiency and sufficient output current. Open

core inductors cause flux linkage with circuit components

and interfere with the normal operation of the circuit. This

should be avoided. For high efficiency, choose an inductor

with a high frequency core material such as ferrite to reduce

the core losses. To minimize radiated noise, use a toroid, pot

core or shielded core inductor. The inductor should be con-

nected to the SW pin as close to the IC as possible. Ex-

amples

of

suitable

inductors

are:

TDK

VLF4012AT-

100MR79, VLF4018BT-100MR90, VLF5014AT-100MR92,

Coilcraft LPS4018-103ML.

LIST OF RECOMMENDED EXTERNAL COMPONENTS

Symbol

Symbol explanation

Value

Unit

Type

C

VDD

C between VDD1,2 and GND

100

nF

Ceramic, X7R / X5R

C

VDDIO

C between VDDIO and GND

100

nF

Ceramic, X7R / X5R

C

VDDA

C between VDDA and GND

1

µF

Ceramic, X7R / X5R

C

OUT

C between FB and GND

2 x 4.7 or1x10

µF

Ceramic, X7R / X5R, tolerance +/-10%

-50

%

C

IN

C between battery voltage and GND

10

µF

Ceramic, X7R / X5R

L

1

L between SW and V

BAT

10

µH

Shielded inductor, low ESR

Saturation current

600

mA

C

VREF

C between V

100

nF

Ceramic, X7R / X5R

R

KEY

R between I

8.2

k

Ω

R

RT

R between I

82

k

Ω

D

1

0.3-0.5

V

Schottky diode

Reverse voltage

30

V

Repetitive peak current

800

mA

C

SW

C in EMI filter

100

pF

Ceramic, X7R / X5R, 50V

R

SW

R in EMI filter

390

Ω

LEDs

User Defined

Note: See Application Note AN-1436 "Design and Programming Examples for Lighting Management Unit LP3958" for more

information on how to design with LP3958

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