LP8543

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SNVS604D – AUGUST 2009 – REVISED MARCH 2013

Example using above equations:

•

•

•

•

L = 15 µH

− 20% = 12 µH

•

f = 1.25 MHz

•

approach is to choose an inductor that has a saturation current rating greater than the maximum current limit of

0.9...2.5A (programmed to EEPROM). Maximum current limit needed for the application can be approximated

with calculations above. A 15

μH inductor with a saturation current rating of 2.5A is recommended for most

applications. The inductor’s resistance should be less than 300 m

Ω for good efficiency. For high efficiency

choose an inductor with high frequency core material such as ferrite to reduce core losses. To minimize radiated

noise, use shielded core inductor. Inductor should be placed as close to the SW pin and the IC as possible.

Special care should be used when designing the PCB layout to minimize radiated noise and to get good

performance from the boost converter.

Output Capacitor

A ceramic capacitor with 50V voltage rating or higher is recommended for the output capacitor. The DC-bias

effect can reduce the effective capacitance by up to 80%, which needs to be considered in capacitance value

selection. For light loads (<100 mA) 4.7 µF capacitor is sufficient. For maximum output voltage/current 10 µF

capacitor (4 uF effective capacitance @ 38V) is recommended to reduce the output ripple. Small 33 pF capacitor

is recommended to use in parallel with the output capacitor to suppress high frequency noise.

LDO Capacitor

A 470 nF ceramic capacitor with 10V voltage rating is recommended for the LDO capacitor.

Output Diode

A schottky diode should be used for the output diode. Peak repetitive current should be greater than inductor

peak current (0.9...2.5A) to ensure reliable operation. Average current rating should be greater than the

maximum output current. 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

significantly larger (~60V) 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.

Ambient Light Sensor

LP8543 uses light-to-frequency type ambient light sensor. Suitable frequency range for ALS is 200 Hz to 2 MHz.

Table 14. LP8543 Register Map

ADDR

REGISTER

D7

D6

D5

D4

D3

D2

D1

D0

DEFAULT

00H

Display1 PWM

DISP1_PWM[7:0]

1111 1111

01H

Config1

PWM_MD

PWM_SEL

BL_CTL

0000 0000

OV_CUR

THRM_SH

02H

Status

2_CH_SD

1_CH_SD

BL_STAT

FAULT

0000 0000

R

DN

LED_PAN

03H

Identification

MFG[3:0]

REV[2:0]

1111 1001

EL

04H

Output Control

OUT[7:1]

0000 0000

Display1

05H

DISP1_CURRENT[7:0]

0000 0000

Current

Display2

06H

DISP2_CURRENT[7:0]

0000 0000

Current

BOOST_A

EN_BOO

07H

Boost Control

VPROG[4:0]

0110 0000

UTO

ST

08H

Display2 PWM

DISP2_PWM[7:0]

0000 0000

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