LP8543

SNVS604D – AUGUST 2009 – REVISED MARCH 2013

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Output Grouping

LP8543 features a total of 7 strings (OUT1-OUT7), which can be arranged into 2 groups (Display1 and Display2).

Display1 refers to backlighting for main display and Display2 refers to lighting for a sub display. Number of

outputs used for Display1 can be defined using EEPROM register bits, as shown in the table below. LP8543

supports a minimum of 4 strings and a maximum of 7 strings for Display1. Outputs must be used in order starting

from OUT1. Unused outputs can be left open. When needed OUT7 can be configured for Display2 and it has its

own current and PWM control registers for independent control. EEPROM default factory setting is 6 outputs for

Display1 and OUT7 for Display2.

Table 1. Output Configurations

OUTPUT_CONF[1:0]

Outputs for Display1

Outputs for Display2

00

OUT1-OUT4

OUT7

01

OUT1-OUT5

OUT7

10

OUT1-OUT6

OUT7

11

OUT1-OUT7

-

LED Current Control

Two 8-bit EEPROM registers, Display1 current and Display2 current (addresses B0H and B1H) hold the

default LED string current for the Display1 and Display2 groups respectively. The default values are read from

EEPROM when the chip is activated. When required the LED current can be adjusted also in the registers

Display1 and Display2 current (addresses 05H and 06H). Use of this register is enabled by setting bit 1 in

Config2 register. Default value for <CURRENT SEL> bit is 0, which means that current values in EEPROM are

used. Current control range is linear from 0 to 60 A with 0.23 mA step. Factory default current for Display1 and

Display2 is 20 mA.

LED On/Off Control

LED strings can be activated with 100% PWM by writing <DRV[7:0]> bits high. All these controls are in Direct

control register.

PWM Control Selection

PWM control of the LED strings can be established through 4 combinations of user configurable options as

shown in the table below. <PM_MD> and <PWM_SEL> bits are part of Config1 Register.

Default setting is external PWM input signal. Each of the option is explained in the following sections.

Table 2. PWM Control Selection

PWM_MD

PWM_SEL

PWM source

1

1

PWM input (Direct control)

0

1

PWM input pin (Duty cycle based), default

1

0

Brightness register

0

0

PWM input pin (Duty cycle based) and Brightness register

In addition Ambient light sensor (when used) and on-chip temperature regulation also influence the output PWM

control. This is described later.

A. Direct PWM Input Control

Display1 group can be directly controlled with external PWM signal (bypassing all the PWM logic) by setting

<PWM_MD> and <PWM_SEL> bits high. Outputs will be active when the PWM input pin is high, and when the

input is low the outputs will be off. Input PWM frequency can vary from 100 Hz to 25 kHz. Display2 is not

controlled with this signal.

Note: In this mode, Ambient Light sensor and PSPWM scheme do not influence the output PWM.

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