Rainbow Electronics MAX1579 User Manual

General Description

The MAX1578/MAX1579 provide four regulated outputs
to meet all the voltage requirements for small active­matrix 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 con­verter for driving up to 8 series white LEDs for back­lighting. 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 need­ed. 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 multi­stage, high-voltage charge pumps generate +15V and

-10V to provide VONand V

OFF

, respectively. Utilizing a
unique clocking scheme and internal drivers, these
charge pumps eliminate parasitic charge-current glitch­es 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 tem­perature 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
+15V at 100µA for V

ON

-10V at 100µA for V

OFF

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

MAX1578/MAX1579

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

PIN-PACKAGE

MAX1578ETG

24 Thin QFN 4mm x 4mm
(T2444-4)

MAX1579ETG

24 Thin QFN 4mm x 4mm
(T2444-4)

MAX1578/MAX1579

See Figure 3 for Typical Application Circuit.

ONBIAS

CD2

GND

NEG

PMPB

CD1

LX

CTRL

PGND

OUT

COMP

CS

CU1

CU3

MAIN

CU2

PMP

POS

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

V

DD

C1P

Pin Configuration

TEMP RANGE

-40°C to +85°C

-40°C to +85°C

MAX1578/MAX1579

Complete Bias and White LED Power Supplies
for Small TFT Displays

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 3, VIN= 3V, CTRL = ONBIAS = IN, TA= -40°C to +85°C, typical values are at TA= +25°C, unless otherwise noted. Note 1)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

IN, CS, C1N, C2N, MAIN, ONBIAS, VDDto GND.....-0.3V to +6V

CTRL to GND..................-0.3V to the lesser of +6V or (V

IN

+ 2V)

LX, OUT to GND.....................................................-0.3V to +37V

COMP to GND .............................................-0.3V to (V

IN

+ 0.3V)

CU1 to MAIN ............................................................-0.3V to +6V

CU2 to CU1..............................................................-0.3V to +6V

CU3 to CU2..............................................................-0.3V to +6V

CU3 to POS............................................................-0.3V to +18V

CU3 to GND ...........................................................-0.3V to +18V

POS to GND ...........................................................-0.3V to +18V

CD1 to MAIN ..........................................................+0.3V to -12V

CD1 to GND .............................................................+0.3V to -6V

CD2 to CD1..............................................................+0.3V to -6V

NEG to CD2..............................................................+0.3V to -6V

NEG, CD2 to GND..................................................+0.3V to -12V

C1P, C2P to GND ...........................................-0.3V to (V

IN

+ 6V)

PMP, PMPB to GND................................-0.3V to (V

MAIN

+ 0.3V)

GND to PGND .......................................................-0.3V to +0.3V

I

LX

...................................................................................1.0A

RMS

Continuous Power Dissipation (TA= +70°C)

24-Pin 4mm x 4mm Thin QFN

(derate 20.8mW/°C above +70°C).............................1667mW

Short-Circuit Duration (MAIN, POS, NEG)..................Continuous

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range.............................-65°C to +150°C

Lead Temperature (soldering, 10s)................................ +300°C

PARAMETER CONDITIONS

MIN

TYP

MAX

UNITS

IN Operating Supply Range 2.7 5.5 V
IN Undervoltage-Lockout (UVLO)

Threshold

Rising edge, 30mV hysteresis 2.1

2.6 V

IN Quiescent Current Switching 3 5 mA

TA = +25°C 0.4 1

IN Shutdown Current V

CTRL

= V

ONBIAS

= 0V

T

A

= +85°C 1

µA

Thermal Shutdown Rising temperature, 20°C hysteresis (typ)

°C

MAIN CHARGE PUMP WITH LINEAR REGULATOR

Main Pump Efficiency I

LOAD

= 25mA, VIN = 3.9V 83 %

VIN ≥ 3.8V in 1.5x mode 9 20

VDD Charge-Pump Open-Loop
Output Impedance

V

IN

≥ 3.0V in 2.0x mode 7.5 20

Ω

Operating Frequency

kHz

VDD Output Voltage Charge-pump pause threshold 5.2 5.5 5.7 V

V

IN

Fal l i ng S w i tchover to 2.0x M od e

V

V

IN

Ri si ng S w i tchover to 1.5x M od e

3.8 3.9 4.0 V

Quiescent Current
(Charge Pumps Only)

V

CTRL

= 0V, ONBIAS = IN

mA

V

MAIN

Regulation Voltage 0.1mA < I

LOAD

< 25mA 4.9 5.0 5.1 V

Discharge Switch Resistance
at V

MAIN

V

ONBIAS

= 0V 1 3 kΩ

POS, NEG CHARGE PUMPS

Operating Frequency

kHz
Duty Cycle 50 %
POS Pump Efficiency I

LOAD

= 100µA 97 %

POS Output Voltage I

LOAD

= 0 to 100µA

V

P OS D i schar g e S w i tch Resi stance

V

ONBIAS

= 0V 3 6 kΩ

NEG Pump Efficiency I

LOAD

= -100µA 97 %

2.35

200 250 300

3.75 3.85 3.95

12.0 15.6 19.5

13.9 14.7 15.3

+160

0.87 1.30

MAX1578/MAX1579

Complete Bias and White LED Power Supplies

for Small TFT Displays

_______________________________________________________________________________________ 3

PARAMETER CONDITIONS

UNITS

NEG Output Voltage I

LOAD

= 0 to -100µA

V

N E G D i schar g e S w i tch Resi stance

V

ONBIAS

= 0V 1.5 3 kΩ

LOGIC INPUT (ONBIAS)

Logic Input Low Voltage

V

Logic Input High Voltage 1.6 V

TA = +25°C

1

Input Current

T

A

= +85°C 1

µA

LED BACKLIGHTING

Efficiency LOAD = 6 LEDs in series at 20mA 84 %
OUT Voltage Range (Note 2)

(V

IN

­32 V

Overvoltage-Lockout (OVLO)
Threshold

V

OUT

rising, 2V hysteresis 32 34 36 V

V

OUT

= 32V, V

CTRL

> 0.24V 10 20 32

1

OUT Input Bias Current

V

OUT

= VIN, V

CTRL

= 0

0.1

µA

ERROR AMPLIFIER

TA = +25°C

CTRL to CS Regulation

V

CTRL

= 1.5V, VIN = 2.7V to

5.5V

T

A

= -40°C to +85°C

V

TA = +25°C

1

CS Input Bias Current VCS = V

CTRL

/ 5

T

A

= +85°C

µA

MAX1578

CTRL Input Resistance V

CTRL

< 1.0V

kΩ

CTRL Dual Mode™ Threshold 5mV hysteresis

mV

CTRL Shutdown Delay (Note 3) 6.5 8.2

ms

CS to COMP Transconductance V

COMP

= 1.0V 32 60 90 µS

CS Regulation Derating Function
Start Temperature

V

CTRL

= 3V, MAX1579 only

°C

CS Regulation Derating Function
Slope

V

CTRL

= 3V, TA = +65°C, MAX1579 only -6

mV/°C

MAX1578, V

CTRL

= 3V

CS Maximum Brightness Clamp
Voltage

MAX1579, V

CTRL

= 3V, TA = +25°C

mV

MAX1578

CS Maximum Brightness Voltage
at CTRL

MAX1579

V

OSCILLATOR

Operating Frequency f

BOOST

0.8 1.0 1.2 MHz

PWM mode 12

Minimum Duty Cycle

Pulse skipping 0

%

Maximum Duty Cycle CTRL = IN, CS = GND 92 95 %

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 3, VIN= 3V, CTRL = ONBIAS = IN, TA= -40°C to +85°C, typical values are at TA= +25°C, unless otherwise noted. Note 1)

Dual Mode is a trademark of Maxim Integrated Products, Inc.

TA = +25°C 0.01
TA = +85°C

TA = +25°C 250 500 780

= +85°C 185

T

A

MAX1579

MIN TYP MAX

-10.2 -9.8 -9.3

0.01

VD1)

0.295 0.300 0.305

0.292 0.300 0.308

0.01

0.03

250 500 780

100 170 240

+42

0.72

10.5

310 327 345
322 340 358

1.635

1.70

MAX1578/MAX1579

Complete Bias and White LED Power Supplies
for Small TFT Displays

4 _______________________________________________________________________________________

Note 1: All devices are 100% production tested at TA= +25°C. Limits over the operating temperature range are guaranteed by design.
Note 2: V

D1

is the forward-voltage drop of diode D1 in Figure 3.

Note 3: Time from CTRL going below the Dual-Mode threshold to IC shutdown.

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 3, VIN= 3V, CTRL = ONBIAS = IN, TA= -40°C to +85°C, typical values are at TA= +25°C, unless otherwise noted. Note 1)

PARAMETER CONDITIONS

MIN

TYP

MAX

UNITS

N-CHANNEL SWITCH

LX On-Resistance ILX = 190mA

1.5 Ω

TA = +25°C

5

LX Leakage Current V

LX

= 28V, CTRL = GND

T

A

= +85°C 1

µA

LX Current Limit Duty cycle = 90%

mA

Typical Operating Characteristics

(Circuit of Figure 3, VIN= 3.6V, I

LED

= 20mA, 4 LEDs, CTRL = IN, TA= +25°C, unless otherwise noted.)

50

55

60

65

70

75

80

85

90

2.5 3.0 3.5 4.0 4.5 5.0 5.5

LED EFFICIENCY vs. V

IN

MAX1578toc02

INPUT VOLTAGE (V)

EFFICIENCY (%)

I

LED

= 2mA

I

LED

= 10mA

I

LED

= 20mA

0

10

5

20

15

25

30

-40 85

LED CURRENT vs. TEMPERATURE

MAX1578toc03

TEMPERATURE (°C)

I

LED

(mA)

10-15 35 60

MAX1579

R

CS

= 13

Ω

MAX1578

R

CS

= 22

Ω

0

5

15

10

20

25

01.00.5 1.5 2.0 2.5

LED CURRENT vs. V

CTRL

MAX1578toc04

CTRL VOLTAGE (V)

I

LED

(mA)

0.82

0.01

500 700 900

LED EFFICIENCY vs. I

90
85
80
75
70
65

EFFICIENCY (%)

60
55
50

0 5 10 15 20 25

4 LEDs

6 LEDs

2 LEDs

LED CURRENT (mA)

LED

8 LEDs

MAX1578toc01