MCU

LP8551

SW

FB

GNDs

EN

ISET

PWM

SCLK

SDA

OUT1

OUT2

OUT3

OUT4

L1

D1

10 V ± 40 V

5.5 V ± 22 V

5V

FSET

15 éH

210 mA ± 400 mA

10 éF

4.7 éF

1 éF

FAULT

Can be left floating

if not used

39 pF

VIN

LP8551

SNVS673E – APRIL 2010 – REVISED SEPTEMBER 2014

www.ti.com

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The LP8551 is designed for LCD backlighting for portable devices, such as laptops and tablets. 4 LED current

sinks allow driving up to 40 LEDs with high efficiency. Boost converter optimizes the system efficiency by

adjusting the LED current driver headroom to optimal level in each case. Due to a flexible input voltage

configuration, the LP8551 can be used also in various applications since the input voltage supports 1x to 5x

series Li-Ion cells. Main limiting factor for output power is inductor current limit, which is calculated in the Detailed

Design Procedure. The following design procedure can be used to select component values for the LP8551.

9.2 Typical Applications

9.2.1 Application Using Internal LDO

Figure 22. LP8551 with Internal LDO

9.2.1.1 Design Requirements

DESIGN PARAMETER

EXAMPLE VALUE

Input voltage range

5.5 V to 22 V

Brightness Control

PWM output frequency

LED Current

Brightness slopes

200-ms linear slope + advanced slope

External set resistors

Enabled

Inductor

10 µH to 33 µH, with 2.5-A saturation current

Boost SW frequency

625 kHz

SW current limit

2.5 A

34

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