Constant Current Sink Outputs LED1, LED2, LED3, LED4

LP5527 has four independent backlight/keypad LED drivers.

All the drivers are regulated constant current sinks. LED

currents are controlled by 8-bit current mode DACs. Every

driver can be controlled in two ways:

1.

Brightness control with constant current drivers

2.

Direct ON/OFF control. The current is pre-set by 8-bit

current mode DAC.

In addition, LED1 driver can be synchronized to audio input

signal amplitude.

By using brightness control user can set brightness of every

single LED by using 8-bit brightness control registers. If

analog audio is available on system the user can use audio

synchronization for synchronizing LED1 to the music. Direct

ON/OFF control is mainly for switching LEDs on and off.

LED Control Register (00 hex) has control bits for direct

on/off control of all the LEDs. Note that the LEDs have to be

turned on in order to control them with audio synchronization

(LED1 only) or brightness control.

The brightness is programmed as described in the following.

I

where:

n = LED[7:0] (8-bit)

step = 15 mA / 255

≈ 0.05882 mA

For example if 13.2 mA is required for driver current:

n = 13.2 mA / (15 mA / 255)

≈ 224

224 = 1110 0000, E0 hex

LED1 to LED4 Brightness Control

LED1[7:0], LED2[7:0] LED3[7:0], LED4[7:0] Register

Driver Current, mA (typical)

0000 0000

0

0000 0001

0.059

0000 0010

0.118

••

1110 0000

13.176

••

1111 1110

14.941

1111 1111

15

LED1 TO LED4 DRIVERS ELECTRICAL CHARACTERISTICS

Limits in standard typeface are for T

=10µF, C

9)

Symbol

Parameter

Condition

Min

Typical

Max

Units

I

MAX

Maximum Sink Current

15

mA

I

LEAKAGE

Leakage Current

V

0.03

µA

I

LED

Current Tolerance

I

11.9

-10

13.2

14.5

+10

mA

%

I

MATCH

Sink Current Matching

Between LED 1 to 4

I

1

%

V

SAT

Saturation Voltage

3.0V

≤ V

IN

≤ 5.5V, Current Decreased

to 95% of the Maximum Sink Current

150

230

mV

Note: Sink current matching is the maximum difference from the average.

www.national.com

12