MCU

LP8550

SW

FB

VLDO

GNDs

EN

ISET

VDDIO

PWM

SCLK

SDA

OUT1

OUT2

OUT3

OUT4

OUT5

OUT6

L1

D1

10V ± 40V

5.5V ± 22V

FILTER

5V

FSET

15 éH

VSYNC

210 mA ± 400 mA

COUT

CIN

10 éF

4.7 éF

CVLDO

1 éF

VDDIO reference voltage

VSYNC signal

120 k

#

100 nF

1 éF

FAULT

Can be left floating

if not used

39 pF

VIN

RISET

RFSET

VBATT

LP8550

SNVS657E – SEPTEMBER 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 LP8550 is designed for LCD backlighting for portable devices, such as laptops and tablets. 6 LED current

sinks allow driving up to 60 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 LP8550 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 LP8550.

9.2 Typical Applications

9.2.1 Typical Application Using Internal LDO

Figure 27. LP8550 with Internal LDO

9.2.1.1 Design Requirements

DESIGN PARAMETER

EXAMPLE VALUE

Input voltage range

5.5...22 V

Brightness Control

PWM input duty cycle (default), I2C can be used as well

PWM output frequency

With RFSET resistor 85 kΩ to 100 kΩ; 9.8 kHz with PSPWM enabled

LED Current

With RISET resistor 15 kΩ; 25 mA/channel

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

36

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