General Description

The MAX1578/MAX1579 provide four regulated outputs

to meet all the voltage requirements for small active-

matrix TFT-LCD displays in handheld devices where

minimum external components and high efficiency are

required. Each device consists of three advanced

charge pumps for LCD bias power and a step-up con-

verter for driving up to 8 series white LEDs for back-

lighting. The input voltage range is from 2.7V to 5.5V.

The charge pumps provide fixed +5V, +15V, and -10V

for the LCD bias circuits. No external diodes are need-

ed. A high-efficiency, fractional (1.5x/2x) charge pump

followed by a low-dropout linear regulator provides +5V

to power the source driver. Automatic mode changing

achieves the highest conversion efficiency. Two multi-

stage, high-voltage charge pumps generate +15V and

unique clocking scheme and internal drivers, these

charge pumps eliminate parasitic charge-current glitch-

es and reduce maximum input current, resulting in low

electromagnetic emissions. The outputs are sequenced

during startup and shutdown. In shutdown, the outputs

are discharged to zero.

The high-efficiency inductor step-up converter drives

up to 8 white LEDs in series with a constant current to

provide backlighting. The series connection allows the

LED currents to be identical for uniform brightness and

minimizes the number of traces to the LEDs. The

MAX1578 regulates constant LED current over the

entire temperature range. The MAX1579 features a tem-

perature derating function to avoid overdriving the

white LEDs during high ambient temperatures, enabling

higher drive current below +42

°C.

The MAX1578/MAX1579 are available in space-saving

24-lead 4mm x 4mm thin QFN packages.

Applications

PDAs, Palmtops

Smart Phones

Internet Appliances

LCD Displays with White LED Backlight

Features

♦ Four Regulators in One Package

♦ Bias Power Using Charge Pumps

+5V at 25mA for Source Driver

No External Diodes Required

Output Sequencing

POS, NEG, and MAIN Are Autodischarged

During Shutdown

♦ LED Backlight Power Using Boost Converter

Series LED Connection for Uniform Illumination

Supports Up to 8 LEDs at 25mA (max)

900mW (max) Power

PWM or Analog Dimming Control

Overvoltage Protection

Low Input/Output Ripple

Soft-Start with Zero Inrush Current

Fast 1MHz PWM Operation for Small

Component Size

Temperature Derating Function (MAX1579)

♦ High Efficiency

Bias: 83% (5.0V at 25mA, 15V/-10V at 100µA)

LED: 84% (6 LEDs at 20mA)

♦ Uses Only Ceramic Capacitors and Only One

Inductor

♦ Independent Enable Inputs for LED and Bias

Power

♦ Thermal-Shutdown Protection

♦ 1µA Shutdown Current

♦ Tiny 4mm x 4mm Thin QFN Package

Complete Bias and White LED Power Supplies

for Small TFT Displays

________________________________________________________________ Maxim Integrated Products

1

19-3359; Rev 0; 8/04

For pricing delivery, and ordering information please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Ordering Information

EVALUATION

KIT

AVAILABLE

PART

TEMP RANGE

PIN-PACKAGE

MAX1578ETG

-40

°C to +85°C

24 Thin QFN 4mm x 4mm

(T2444-4)

MAX1579ETG

-40

°C to +85°C

24 Thin QFN 4mm x 4mm

(T2444-4)

See Figure 3 for Typical Application Circuit.

ONBIAS

CD2

GND

NEG

PMPB

CD1

19

20

21

22

23

24

1

2

3

4

5

6

18

17

16

15

14

13

12

11

10

9

8

7

MAX1578

MAX1579

THIN QFN

4mm x 4mm

C2N

C2P

C1N

IN

C1P

Pin Configuration