Rainbow Electronics MAX8758 User Manual

General Description

The MAX8758 includes a high-performance step-up regulator, a high-speed operational amplifier, and a logiccontrolled, high-voltage switch-control block with programmable delay. The device is optimized for thin-film transistor (TFT) liquid-crystal display (LCD) applications.

The step-up DC-DC regulator provides the regulated supply voltage for the panel source driver ICs. The converter is a high-frequency (640kHz/1.2MHz), current-mode regulator with an integrated 14V n-channel power MOSFET. The high-switching frequency allows the use of ultra-small inductors and ceramic capacitors. The current-mode control architecture provides fast transient response to pulsed loads. The regulator achieves efficiencies over 85% by bootstrapping the supply rail of the internal gate driver from the step-up regulator output. The step-up regulator features undervoltage lockout (UVLO), soft-start, and internal current limit. The high-current operational amplifier is designed to drive the LCD backplane (VCOM). The amplifier features high output current (±150mA), fast slew rate (7.5V/µs), wide bandwidth (12MHz), and rail-to-rail inputs and outputs.

The MAX8758 is available in a 24-pin, 4mm x 4mm, thin QFN package with a maximum thickness of 0.8mm for ultra-thin LCD panels. The device operates over the

-40°C to +85°C temperature range.

Applications

Notebook Displays

LCD Monitors

Features

♦ 1.8V to 5.5V Input Voltage Range

♦ Input Undervoltage Lockout

♦ 0.5mA Quiescent Current

♦ 640kHz/1.2MHz Current-Mode Step-Up Regulator

Fast Transient Response High-Accuracy Output Voltage (1.5%) Built-In 14V, 2.5A, 115mΩ MOSFET High Efficiency Programmable Soft-Start Current Limit with Lossless Sensing Timer-Delay Fault Latch

♦ High-Speed Operational Amplifier

±150mA Output Current

7.5V/µs Slew Rate 12MHz, -3dB Bandwidth Rail-to-Rail Inputs/Outputs

♦ Dual-Mode™, Logic-Controlled, High-Voltage

Switch with Programmable Delay

♦ Thermal-Overload Protection

♦ 24-Pin, 4mm x 4mm, Thin QFN Package

MAX8758

Step-Up Regulator with Switch Control and

Operational Amplifier for TFT LCD

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

MAIN

TO VCOM BACKPLANE

GON

FROM TCON

GOFF

FREQ

SHDN

COMP

LDO

GND

PGND

OUT

SUPB

GON

DRN

CTL

MODE

POSB

NEGB

OUTB

THR

DLP

SRC

MAX8758

Simplified Operating Circuit

19-3699; Rev 0; 5/05

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.

PART

PIN-PACKAGE

MAX8758ETG

24 Thin QFN-EP* 4mm x 4mm

Pin Configuration appears at end of data sheet.

DualMode is a trademark of Maxim Integrated Products, Inc.

*EP = Exposed pad.

TEMP RANGE

-40°C to +85°C

MAX8758

Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= V

SHDN

= +3V, OUT = +10V, FREQ = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

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, SHDN, CTL, LDO to GND ...................................-0.3V to +6V

SUPB, LX, OUT to GND..........................................-0.3V to +14V

OUTB, NEGB, POSB to GND ..................-0.3V to (SUPB + 0.3V)

THR, DLP, MODE, FREQ, COMP, FB,

SS to GND..............................................-0.3V to V

LDO

+ 0.3V

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

SRC to GND ..........................................................-0.3V to + 30V

GON, DRN to GND ....................................-0.3V to V

SRC

+ 0.3V

GON RMS Current Rating................................................± 50mA

OUTB RMS Current Rating ..............................................± 60mA

LX RMS Current Rating .........................................................1.6A

Continuous Power Dissipation (TA= +70°C)

24-Pin, 4mm x 4mm Thin QFN

(derate 16.9mW/°C above +70°C)..........................1349.1mW

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

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

Storage Temperature Range .............................-65°C to +160°C

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

PARAMETER CONDITIONS

MIN

TYP

MAX

UNITS

IN Input Voltage Range 1.8 5.5 V

IN Quiescent Current VIN = 3V, VFB = 1.5V 27 40 µA

IN Undervoltage Lockout

IN rising, 200mV hysteresis, LX remains off below this level

1.3

LDO Output Voltage

4.8 5.0 5.2 V

LDO Undervoltage Lockout Voltage LDO rising, 200mV hysteresis 2.4 2.7 3.0 V

OUT Supply Voltage Range (Note 1) 4.5

OUT Overvoltage Fault Threshold

OUT Undervoltage Fault Threshold 1.4 V

VFB = 1.5V, no load 0.5 2.0

OUT Supply Current

= 1.1V, no load 4

Shutdown Supply Current (Total of IN, OUT, and SUPB)

= V

OUT

= V

SUPB

= 3V 4 10 µA

Thermal Shutdown Temperature rising, 15°C hysteresis

°C

STEP-UP REGULATOR

FREQ = GND

768

Operating Frequency

FREQ = IN

kHz

FREQ = GND 91 95 99

Oscillator Maximum Duty Cycle

FREQ = IN 88 92 96

FB Regulation Voltage

FB Fault Trip Level Falling edge

1.0

FREQ = GND 43 51 64

Duration to Trigger Fault Condition

FREQ = IN 47 55 65

FB Load Regulation 0 < I

LOAD

< 200mA, transient only -1 %

FB Line Regulation V

= 1.8V to 5.5V

%/V

FB Input Bias Current VFB = 1.3V

200 nA

FB Transconductance ∆I = 5µA at COMP 75

280 µS

FB Voltage Gain FB to COMP

V/V

LX On-Resistance I

= 200mA

200 mΩ

1.75

6V ≤ V

≤ 13V, I

OUT

= 12.5mA, VFB = 1.5V (Note1)

LDO

13.2 13.6 14.0

+160

512 600

1020 1200 1380

1.228 1.24 1.252

0.96

-0.15 -0.08 +0.15

125

160

700

115

13.0

10.0

1.04

MAX8758

Step-Up Regulator with Switch Control and

Operational Amplifier for TFT LCD

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VIN= V

SHDN

= +3V, OUT = +10V, FREQ = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER CONDITIONS

MIN

TYP

MAX

UNITS

LX Leakage Current V

= 13V

20 µA

LX Current Limit 65% duty cycle 2.0 2.5 3.0 A

Current-Sense Transresistance

0.3

V/A

SS Source Current 3.0 4.0 5.5 µA

POSITIVE GATE DRIVER TIMING AND CONTROL SWITCHES

CTL Input Low Voltage VIN = 1.8V to 5.5V 0.6 V

VIN = 1.8V to 2.4V 1.4

CTL Input High Voltage

= 2.4V to 5.5V 2.0

CTL Input Leakage Current V

CTL

= 0 or V

-1 +1 µA

GON rising, V

MODE

= 1.24V, V

CTL

= 0 to 3V step,

no load on GON

CTL-to-SRC Propagation Delay

GON falling, V

MODE

= 1.24V, V

CTL

= 3V to 0 step,

no load on GON

SRC Input Voltage

DLP

= 0, VIN = 3V

Ω

SRC Input Current MODE = DLP = CTL = LDO

250 µA

DRN Input Current MODE = DLP = LDO, V

DRN

= 8V, V

CTL

= 0

250 µA

SRC-to-GON Switch On-Resistance DLP = CTL = LDO 15 30 Ω

DRN-to-GON Switch On-Resistance DLP = LDO, V

CTL

= 0 65 130 Ω

GON-to-PGND Switch On-Resistance

DLP

= 0, VIN = 3V

Ω

MODE Switch On-Resistance V

DLP

= 0, VIN = 3V

Ω

MODE 1 Voltage Threshold MODE rising

MODE Capacitor Charge Current (MODE 2)

MODE

= 1.5V 40 50 62 µA

MODE 2 Switch Transition Voltage Threshold

GON connected to DRN 2.3 2.5 2.7 V

MODE Current-Source Stop Threshold

MODE rising 3.3 3.5 3.7 V

DLP Capacitor Charge Current During startup, V

DLP

= 1.0V 4 5 6 µA

DLP Turn-On Threshold

THR-to-GON Voltage Gain V

GON

= 12V, V

THR

= 1.2V 9.7

V/V

OPERATIONAL AMPLIFIER

SUPB Supply Range 4.5

SUPB Supply Current Buffer configuration, V

POSB

= 4V, no load 1.0 mA

Input Offset Voltage V

NEGB

, V

POSB

= V

SUPB

/2, TA = +25°C 12 mV

Input Bias Current V

NEGB

, V

POSB

= V

SUPB

/2 -50

Input Common-Mode Voltage Range

0.01

0.19

100

2500

150

2500

1000

0.9 x V

LDO

2.375 2.500 2.625

10.0 10.3

0.40

13.0

+50

SUPB

MAX8758

Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VIN= V

SHDN

= +3V, OUT = +10V, FREQ = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER CONDITIONS

UNITS

OUTB

= 100µA

SUPB

Output Voltage Swing High

OUTB

= 5mA

SUPB

OUTB

= -100µA 15

Output Voltage Swing Low

OUTB

= -5mA 150

Slew Rate 7.5 V/µs

-3dB Bandwidth 12

MHz

Gain-Bandwidth Product 8

MHz

OUTB shorted to V

SUPB

/2, sourcing 75

Short-Circuit Current

OUTB shorted to V

SUPB

/2, sinking 75

CONTROL INPUTS

FREQ Input Low Voltage V

= 1.8V to 5.5V 0.6 V

= 1.8V to 2.4V 1.4

FREQ Input High Voltage

= 2.4V to 5.5V 2.0

FREQ Pulldown Current V

FREQ

= 1.0V 3.5 5.0 6.0 µA

SHDN Input Low Voltage V

= 1.8V to 5.5V 0.6 V

= 1.8V to 2.4V 1.4

= 2.4V to 3.6V 2.0

SHDN Input High Voltage

= 3.6V to 5.5V 2.9

SHDN Input Current

1.0 µA

ELECTRICAL CHARACTERISTICS

(VIN= V

SHDN

= +3V, OUT = +10V, FREQ = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

PARAMETER CONDITIONS

MIN

TYP

MAX

UNITS

IN Input Voltage Range 1.8 5.5 V

IN Quiescent Current VIN = 3V, VFB = 1.5V 30 µA

IN Undervoltage Lockout

IN rising, 200mV hysteresis, LX remains off below this level

LDO Output Voltage

6V ≤ V

OUT

≤ 13V, I

LDO

= 12.5mA, VFB = 1.5V

(Note 1)

4.8 5.2 V

LDO Undervoltage Lockout Voltage LDO rising, 200mV hysteresis 2.4 3.0 V

OUT Supply Voltage Range (Note 1) 4.5

VFB = 1.5V, no load 2.0

OUT Supply Current

= 1.1V, no load

STEP-UP REGULATOR

FREQ = GND

Operating Frequency

FREQ = IN

kHz

MIN TYP MAX

150

0.001

512 768

990 1380

1.75

13.0

10.0

PARAMETER CONDITIONS

MIN

TYP

MAX

UNITS

FREQ = GND 91 99

Oscillator Maximum Duty Cycle

FREQ = IN 88 96

FB Regulation Voltage

FB Transconductance ∆I = 5µA at COMP 75

µS

LX On-Resistance I

= 200mA

mΩ

LX Current Limit 65% duty cycle 2.0 3.0 A

POSITIVE GATE DRIVER TIMING AND CONTROL SWITCHES

SRC Input Voltage Range 28 V

SRC Input Current MODE = DLP = CTL = LDO

µA

DRN Input Current MODE = DLP = LDO, V

DRN

= 8V, V

CTL

= 0

µA

SRC-to-GON Switch On-Resistance DLP = CTL = LDO 30 Ω

DRN-to-GON Switch On-Resistance DLP = LDO, V

CTL

= 0

Ω

THR-to-GON Voltage Gain V

GON

= 12V, V

THR

= 1.2V 9.7

V/V

OPERATIONAL AMPLIFIER

SUPB Supply Range 4.5

SUPB Supply Current Buffer configuration, V

POSB

= 4V, no load 1.0 mA

Input Offset Voltage V

NEGB

, V

POSB

= V

SUPB

/ 2 18 mV

Input Common-Mode Voltage Range

OUTB

= 100µA

SUPB

Output Voltage Swing High

OUTB

= 5mA

SUPB

OUTB

= -100µA 15

Output Voltage Swing Low

OUTB

= -5mA

OUTB shorted to V

SUPB

/2, sourcing 75

Short-Circuit Current

OUTB shorted to V

SUPB

/2, sinking 75

MAX8758

Step-Up Regulator with Switch Control and

Operational Amplifier for TFT LCD

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS (continued)

(VIN= V

SHDN

= +3V, OUT = +10V, FREQ = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

Note 1: OUT and SUP can operate down to 4.5V. LDO will be out of regulation, but IC will function correctly. Note 2: -40°C specs are guaranteed by design, not production tested.

1.220 1.252

280

200

250

130

10.3

13.0

SUPB

- 15

- 150

150

MAX8758

Step-Up Regulator with Switch Control and Operational Amplifier for TFT LCD

6 _______________________________________________________________________________________

Typical Operating Characteristics

(Circuit of Figure 1, VIN= 3.3V, V

MAIN

= 8.5V, FREQ = SHDN = IN, TA= +25°C, unless otherwise noted.)

STEP-UP REGULATOR EFFICIENCY

vs. LOAD CURRENT (V

MAIN

= 8.5V)

MAX8758 toc01

LOAD CURRENT (mA)

EFFICIENCY (%)

10010

11000

OSC

= 1.2MHz

L = 4.7µH

VIN = 5.5V

VIN = 1.8V

VIN = 3.3V

STEP-UP REGULATOR EFFICIENCY

vs. LOAD CURRENT (V

MAIN

= 8.5V)

MAX8758 toc02

LOAD CURRENT (mA)

EFFICIENCY (%)

10010

1 1000

OSC

= 640kHz

L = 10µH

VIN = 5.5V

VIN = 1.8V

VIN = 3.3V

OUTPUT VOLTAGE (V)

8.0

8.1

8.2

8.3

8.4

8.5

8.6

7.9

STEP-UP REGULATOR OUTPUT VOLTAGE

vs. LOAD CURRENT (V

MAIN

= 8.5V)

MAX8758 toc03

LOAD CURRENT (mA)

100101 1000

OSC

= 1.2Hz

= 3.3V

IN QUIESCENT CURRENT

vs. SUPPLY VOLTAGE

MAX8758 toc04

VIN (V)

SUPPLY CURRENT (µA)

5.04.54.03.53.02.52.0

1.5 5.5

CURRENT INTO IN PIN

NOT SWITCHING V

- 1.5V

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

603510-15

-40 85

IN QUIESCENT CURRENT

vs. TEMPERATURE

MAX8758 toc05

CURRENT INTO IN PIN

VIN = 3.3V NOT SWITCHING V

- 1.5V

SWITCHING FREQUENCY

vs. INPUT VOLTAGE

MAX8758 toc06

VIN (V)

SWITCHING FREQUENCY (kHz)

4.53.52.5

600

800

1000

1200

400

1.5 5.5

FREQ = V

FREQ = AGND

MAIN

= 200mA

STEP-UP REGULATOR HEAVY-LOAD

SOFT-START

MAX8758 toc07

1ms

2V/div

MAIN

5V/div

500mAV/div

STEP-UP REGULATOR LOAD TRANSIENT

RESPONSE

MAX8758 toc08

20µs/div

MAIN

AC-COUPLED 200mV/div

L = 4.7µH

COMP

= 100k

Ω

COMP1

= 220pF

COMP2

= 47pF

50mA

MAIN

500mA/div

1AV/div

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