LP55281

www.ti.com

SNVS458B – JUNE 2007 – REVISED JUNE 2007

A Schottky diode should be used for the output diode. To maintain high efficiency the average current rating of

the schottky diode shoulde be larger than the peak inductor current (1A). 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, L:

The LP55281'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 peak current it will experience during circuit operation (~1A). 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. To minimize radiated

noise, use a toroid, pot core or shielded core inductor. The inductor should be connected to the SW pin as close

to the IC as possible. Recommended inductors are LPS3015 and LPS4012 from Coilcraft and VLF4012 from

TDK.

LIST OF RECOMMENDED EXTERNAL COMPONENTS

Symbol

Symbol explanation

Value

Unit

Type

100

nF

Ceramic, X7R/X5R

100

nF

Ceramic, X7R/X5R

100

nF

Ceramic, X7R/X5R

1

µF

Ceramic, X7R/X5R

C between FB and GND

10

µF

Ceramic, X7R/X5R

C between battery voltage and GND

10

µF

Ceramic, X7R/X5R

L between SW and VBAT at 2 MHz

4.7

µH

C between VREF and GND

100

nF

Ceramic, X7R

100

nF

Ceramic, X7R

R between IRGB and GND

8.2

k

Ω

±1%

R between IRT and GND

82

k

Ω

±1%

0.3

V

Schottky diode

C between Audio input and ASEx

100

nF

Ceramic, X7R/X5R

LEDs

User defined

LP55281 Registers

Following table summarizes the registers and their default values

Address

Register

D7

D6

D5

D4

D3

D2

D1

D0

00h

RED1

R1 - IPLS[7:6]

R1_PWM[5:0]

0

0

0

0

0

0

0

0

01h

GREEN1

G1 - IPLS[7:6]

G1_PWM[5:0]

0

0

0

0

0

0

0

0

02h

BLUE1

B1 - IPLS[7:6]

B1_PWM[5:0]

0

0

0

0

0

0

0

0

03h

RED2

R2 - IPLS[7:6]

R2_PWM[5:0]

0

0

0

0

0

0

0

0

04h

GREEN2

G2 - IPLS[7:6]

G2_PWM[5:0]

0

0

0

0

0

0

0

0

05h

BLUE2

B2 - IPLS[7:6]

B2_PWM[5:0]

0

0

0

0

0

0

0

0

Copyright © 2007, Texas Instruments Incorporated

Submit Documentation Feedback

27

Product Folder Links: LP55281