LP3952RLSLASHNOPB datasheet(29/46 Pages) TI1

29 / 46 page

LP3952

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SNVS518A – JULY 2007 – REVISED MARCH 2013

Autoincrement mode is available, with this mode it is possible to read or write bytes with autoincreasing

addresses. LP3952 has empty spaces in address register map, and it is recommended to use autoincrement

mode only for writing in pattern command registers.

Recommended External Components

OUTPUT CAPACITOR, COUT

The output capacitor COUT directly affects the magnitude of the output ripple voltage. In general, the higher the

value of COUT, the lower the output ripple magnitude. Multilayer ceramic capacitors with low ESR are the best

choice. At the lighter loads, the low ESR ceramics offer a much lower Vout ripple that the higher ESR tantalums

of the same value. At the higher loads, the ceramics offer a slightly lower Vout ripple magnitude than the

tantalums of the same value. However, the dv/dt of the Vout ripple with the ceramics is much lower than the

tantalums under all load conditions. Capacitor voltage rating must be sufficient, 10V or greater is recommended.

Some ceramic capacitors, especially those in small packages, exhibit a strong capacitance reduction

with the increased applied DC voltage, so called DC bias effect. The capacitance value can fall to below

half of the nominal capacitance. Too low output capacitance will increase noise and it can make the

boost converter unstable. Recommended maximum DC bias effect at 5V DC voltage is -50%.

INPUT CAPACITOR, CIN

The input capacitor CIN directly affects the magnitude of the input ripple voltage and to a lesser degree the VOUT

ripple. A higher value CIN will give a lower VIN ripple. Capacitor voltage rating must be sufficient, 10V or greater is

recommended.

OUTPUT DIODE, D1

A schottky diode should be used for the output diode. Peak repetitive current rating of the schottky diode should

be larger than the peak inductor current (ca. 1A). Average current rating of the schottky diode should be higher

than maximum output current used. Schottky diodes with a low forward drop and fast switching speeds are ideal

for increasing efficiency in portable applications. Choose a reverse breakdown of the schottky diode larger than

the output voltage. Do not use ordinary rectifier diodes, since slow switching speeds and long recovery times

cause the efficiency and the load regulation to suffer.

INDUCTOR, L1

The LP3952’s high switching frequency enables the use of the small surface mount inductor. A 4.7

μH shielded

inductor is suggested for 2 MHz operation, 10

μH should be used at 1 MHz. The inductor should have a

saturation current rating higher than the rms current it will experience during circuit operation. To get maximum

(400 mA) current from the boost, an inductor with 1A saturation current is recommended. If output current is for

example 200 mA then inductor with 600 mA saturation current can be used. Less than 300 m

Ω ESR is

suggested for high efficiency. 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. The inductor should be connected to the SW

pin as close to the IC as possible. Examples of suitable inductor for 400 mA output current is TDK VLF4012AT-

4R7M1R1, and for 200mA application VLF3010AT-4R7MR70 or Panasonic ELLVEG4R7N.

LIST OF RECOMMENDED EXTERNAL COMPONENTS

Symbol

Symbol explanation

Value

Unit

Type

CVDD1

C between VDD1 and GND

100

Ceramic, X7R / X5R

CVDD2

C between VDD2 and GND

100

Ceramic, X7R / X5R

CVDDIO

C between VDDIO and GND

100

Ceramic, X7R / X5R

CVDDA

C between VDDA and GND

μF

Ceramic, X7R / X5R

COUT

C between FB and GND

μF

Ceramic, X7R / X5R, 10V

CIN

C between battery voltage and GND

μF

Ceramic, X7R / X5R

L between SW and VBAT at 2 MHz

4.7

μH

Shielded, low ESR, Isat=1A for 400

mA output current, Isat=600 mA for

200 mA output current

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