LP8545 datasheet(28/44 Pages) TI1

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LP8545

SNVS635D – APRIL 2010 – REVISED DECEMBER 2013

www.ti.com

LDO Capacitor

A 1µF 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 (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.

Boost Converter Transistor

FET transistor with high enough voltage rating (VDS at least 60V) should be used. Current rating for the FET

should be the same as inductor peak current (2.5A with highest programmed inductor current). Gate drive

voltage for the FET is 5V.

Resistor Divider for the Boost Feedback

Recommended values for feedback resistor divider to get 55V boost output voltage are R1 = 63.4 kΩ and R2 =

59 k

Ω. Resistor values can be fine tuned to get desired maximum boost output voltage based on how many

LEDs are driven in series and what are the forward voltage specifications for the LEDs. Voltage on FB pin must

not exceed 40V any time.

Resistors For Setting The LED Current and PWM Frequency

See Table 3 on how to select values for these resistors

Filter Component Values

Optimal components for 60 Hz VSYNC frequency and 4 Hz cut-off frequency of the low-pass filter are shown in the

Typical Application Diagrams and in the figure below. If 2 Hz cut-off frequency i.e. slower response time is

desired, filter components are: C1 = 1 µF, C2 = 10 µF and R = 47 kΩ. If different VSYNC frequency or response

time is desired, please contact TI representative for guidance.

Table 2. Register Map

ADDR

DEFAULT

00H

Brightness

BRT[7:0]

0000 0000

Control

01H

Device Control

BRT_MODE[1:0]

BL_CTL

0000 0000

02H

Fault

OPEN

SHORT

2_CHANN 1_CHANN

BL_FAULT

OCP

TSD

UVLO

0000 0000

ELS

03H

PANEL

MFG[3:0]

REV[2:0]

1111 1100

04H

Direct Control

OUT[6:1]

0000 0000

05H

Temp MSB

TEMP[10:3]

0000 0000

06H

Temp LSB

TEMP[2:0]

0000 0000

72H

EEPROM_con EE_READ

EE_INIT

EE_PROG

EE_READ 0000 0000

trol

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