LP8551TLXSLASHNOPB datasheet(36/46 Pages) TI2

36 / 46 page

MCU

LP8551

VLDO

GNDs

ISET

VDDIO

PWM

SCLK

SDA

OUT1

OUT2

OUT3

OUT4

2.7 V...

+5V input rail

FSET

15 éH

COUT

CIN

10 éF

4.7 éF

CVLDO

1 éF

VDDIO reference voltage

RISET

FAULT

Can be left floating

if not used

39 pF

VIN

RFSET

VBATT

10 V ± 40 V *

*) Conversion ratio of 10

should not be exceeded

LP8551

SNVS673E – APRIL 2010 – REVISED SEPTEMBER 2014

www.ti.com

9.2.1.2.1.3

LDO Capacitor

A 1-

μF ceramic capacitor with 10-V voltage rating is recommended for the LDO capacitor.

9.2.1.2.1.4

Output Diode

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

peak current (2.5 A) 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

(approximately 60 V) 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.

9.2.1.3 Application Curves

Typical Boost and LED Current waveforms with ƒLED= 9.6 kHz.

Figure 23. 10% LED PWM Duty Cycle

Figure 24. 60% LED PWM Duty Cycle

9.2.2 Application with Low-Input Voltage

In Single Li-Ion cell powered application the internal circuitry of LP8551 can be powered from external 5-V rail.

Boost is powered directly from Li-Ion battery and VLDO and VIN pins are connected to external 5-V rail. Current

draw from the 5-V rail is maximum 10 mA. A separate 5-V rail to VIN/VLDO can be used also in higher input

voltage application to improve efficiency or add increase input voltage range above 22 V in some cases. There

are no power sequencing requirement for VIN/VLDO and VBATT other than VBATT must be available when enabling

backlight to prevent a false overcurrent fault.

Figure 25. LP8551 with Low-Input Voltage

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