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

V

MAIN

TO VCOM
BACKPLANE

V

GON

FROM TCON

V

IN

V

GOFF

IN

FREQ

SHDN

COMP

LDO

FB

LX

GND

PGND

OUT

SUPB

GON

DRN

CTL

MODE

SS

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

V

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

V

OUT Overvoltage Fault Threshold

V

OUT Undervoltage Fault Threshold 1.4 V

VFB = 1.5V, no load 0.5 2.0

OUT Supply Current

V

FB

= 1.1V, no load 4

mA

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

V

IN

= 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

V

FB Fault Trip Level Falling edge

1.0

V

FREQ = GND 43 51 64

Duration to Trigger Fault Condition

FREQ = IN 47 55 65

ms

FB Load Regulation 0 < I

LOAD

< 200mA, transient only -1 %

FB Line Regulation V

IN

= 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

LX

= 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

LX

= 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

V

IN

= 2.4V to 5.5V 2.0

V

CTL Input Leakage Current V

CTL

= 0 or V

IN

-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

ns

SRC Input Voltage

V

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

V

DLP

= 0, VIN = 3V

Ω

MODE Switch On-Resistance V

DLP

= 0, VIN = 3V

Ω

MODE 1 Voltage Threshold MODE rising

V

MODE Capacitor Charge Current
(MODE 2)

V

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

V

THR-to-GON Voltage Gain V

GON

= 12V, V

THR

= 1.2V 9.7

V/V

OPERATIONAL AMPLIFIER

SUPB Supply Range 4.5

V

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

nA

Input Common-Mode Voltage Range

0

V

0.01

0.19

100

100

2500

150

150

2500

1000

0.9 x
V

LDO

2.375 2.500 2.625

10.0 10.3

0.40

13.0

+50

V

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

I

OUTB

= 100µA

V

SUPB

-

15

Output Voltage Swing High

I

OUTB

= 5mA

V

SUPB

-

mV

I

OUTB

= -100µA 15

Output Voltage Swing Low

I

OUTB

= -5mA 150

mV

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

mA

CONTROL INPUTS

FREQ Input Low Voltage V

IN

= 1.8V to 5.5V 0.6 V

V

IN

= 1.8V to 2.4V 1.4

FREQ Input High Voltage

V

IN

= 2.4V to 5.5V 2.0

V

FREQ Pulldown Current V

FREQ

= 1.0V 3.5 5.0 6.0 µA

SHDN Input Low Voltage V

IN

= 1.8V to 5.5V 0.6 V

V

IN

= 1.8V to 2.4V 1.4

V

IN

= 2.4V to 3.6V 2.0

SHDN Input High Voltage

V

IN

= 3.6V to 5.5V 2.9

V

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

V

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

V

VFB = 1.5V, no load 2.0

OUT Supply Current

V

FB

= 1.1V, no load

mA

STEP-UP REGULATOR

FREQ = GND

Operating Frequency

FREQ = IN

kHz

MIN TYP MAX

150

150

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

V

FB Transconductance ∆I = 5µA at COMP 75

µS

LX On-Resistance I

LX

= 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

V

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

0

V

I

OUTB

= 100µA

V

SUPB

Output Voltage Swing High

I

OUTB

= 5mA

V

SUPB

mV

I

OUTB

= -100µA 15

Output Voltage Swing Low

I

OUTB

= -5mA

mV

OUTB shorted to V

SUPB

/2, sourcing 75

Short-Circuit Current

OUTB shorted to V

SUPB

/2, sinking 75

mA

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

250

130

10.3

13.0

V

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

55

60

65

70

75

80

85

90

95

50

11000

f

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

55

60

65

70

75

80

85

90

95

50

1 1000

f

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

f

OSC

= 1.2Hz

V

IN

= 3.3V

IN QUIESCENT CURRENT

vs. SUPPLY VOLTAGE

MAX8758 toc04

VIN (V)

SUPPLY CURRENT (µA)

5.04.54.03.53.02.52.0

10

20

30

40

50

0

1.5 5.5

CURRENT INTO IN PIN

NOT SWITCHING
V

FB

- 1.5V

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

603510-15

25

26

27

28

29

30

24

-40 85

IN QUIESCENT CURRENT

vs. TEMPERATURE

MAX8758 toc05

CURRENT INTO IN PIN

VIN = 3.3V
NOT SWITCHING
V

FB

- 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

IN

FREQ = AGND

I

MAIN

= 200mA

STEP-UP REGULATOR HEAVY-LOAD

SOFT-START

MAX8758 toc07

1ms

V

IN

2V/div

V

MAIN

5V/div

I

L

500mAV/div

STEP-UP REGULATOR LOAD TRANSIENT

RESPONSE

MAX8758 toc08

20µs/div

V

MAIN

AC-COUPLED
200mV/div

L = 4.7µH

R

COMP

= 100k

Ω

C

COMP1

= 220pF

C

COMP2

= 47pF

50mA

0

I

MAIN

500mA/div

I

L

1AV/div

MAX8758

Step-Up Regulator with Switch Control and

Operational Amplifier for TFT LCD

_______________________________________________________________________________________ 7

STEP-UP REGULATOR PULSED LOAD

TRANSIENT RESPONSE

MAX8758 toc09

20µs/div

V

MAIN

AC-COUPLED
200mV/div

L = 4.7µH

R

COMP

= 100k

Ω

C

COMP1

= 220pF

C

COMP2

= 47pF

I

MAIN

1A/div

I

L

1AV/div

TIMER-DELAY LATCH RESPONSE

TO OVERLOAD

MAX8758 toc10

20ms/div

V

MAIN

5V/div

LX
5V/div

I

L

2A/div

0A

0V

0V

MAX8758 toc11

SUPB SUPPLY CURRENT

vs. SUPB VOLTAGE

V

SUPB

(V)

I

SUPB

(mA)

4.5 6.0 7.5 9.0 10.5 12.0 13.5 15.0

0.10

0.15

0.20

0.25

0.30
NO LOAD
BUFFER CONFIGURATION
POS_ = V

SUPB

/ 2

MAX8758 toc12

SUPB SUPPLY CURRENT

vs. TEMPERATURE

TEMPERATURE (°C)

I

SUPB

(mA)

-40 -10 20 50 70

0.10

0.15

0.20

0.25

0.30
NO LOAD
BUFFER CONFIGURATION
V

POSB

= V

SUPB

/ 2

V

SUPB

= 12V

V

SUPB

= 8V

V

SUPB

= 5V

OPERATIONAL AMPLIFIER FREQUENCY

RESPONSE FOR VARIOUS C

LOAD

MAX8758 toc13

FREQUENCY (Hz)

MAGNITUDE (dB)

10k1k

-40

-30

-20

-10

0

10

-50
100 100k

V

SUP

= 8.5V

A

V

= 1

R

L

= 10k

Ω

1000pF

56pF

POWER-SUPPLY REJECTION RATIO

vs. FREQUENCY

MAX8758 toc14

FREQUENCY (Hz)

PSRR (dB)

100k10k1k10010

20

40

60

80

100

120

0

11M

V

SUPB

= 8.5V

OP-AMP RAIL-TO-RAIL INPUT/OUTPUT

MAX8758 toc15

100µs/div

V

POSB

5V/div

V

OUTB

5V/div

OP-AMP LOAD TRANSIENT RESPONSE

MAX8758 toc16

1µs/div

I

OUTB

50mA/div

0

V

OUTB

2V/div

Typical Operating Characteristics (continued)

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

MAIN

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

MAX8758

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

8 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

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

MAIN

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

OP-AMP LARGE-SIGNAL STEP RESPONSE

MAX8758 toc17

1µs/div

V

OUTB

2V/div

OP-AMP SMALL-SIGNAL STEP RESPONSE

MAX8758 toc18

200ns/div

V

POSB

100mV/div
AC-COUPLED

V

OUTB

200mV/div
AC-COUPLED

HIGH-VOLTAGE SWITCH CONTROL FUNCTION

(MODE 1)

MAX8758 toc19

400µs/div

V

MODE

V

CTL

V

GON

HIGH-VOLTAGE SWITCH CONTROL FUNCTION

(MODE 2)

MAX8758 toc20

400µs/div

V

MODE

V

CTL

V

GON

POSITIVE CHARGE-PUMP OUTPUT VOLTAGE

vs. CHARGE-PUMP LOAD CURRENT

MAX8758 toc21

CHARGE-PUMP LOAD CURRENT (mA)

OUTPUT VOLTAGE (V)

15105

21

22

23

24

25

20

020

VIN = 3.3V
f

OSC

= 1.2MHz

-9

-8

-7

-6

-5

-10

NEGATIVE CHARGE-PUMP OUTPUT VOLTAGE

vs. LOAD CURRENT

MAX8758 toc22

CHARGE-PUMP LOAD CURRENT (mA)

OUTPUT VOLTAGE (V)

15105020

VIN = 3.3V
f

OSC

= 1.2MHz

MAX8758

Step-Up Regulator with Switch Control and

Operational Amplifier for TFT LCD

_______________________________________________________________________________________ 9

Pin Description

PIN NAME FUNCTION

1 GND Analog Ground

2 GON

Internal High-Voltage-Switch Common Connection. GON is the output of the high-voltage-switch­control block. GON is internally pulled to PGND through a 1kΩ resistor in shutdown. See the High-
Voltage Switch Control section for details.

3 CTL H i g h- V ol tag e, S w i tch- C ontr ol Bl ock Ti m i ng P i n. S ee the H i g h- V ol tag e S w i tch C ontr ol secti on for d etai l s.

4 DLP

High-Voltage, Switch-Control Block Delay Pin. Connect a capacitor from DLP to GND to set the delay
time. A 5µA current source charges C

DLP

. DLP is internally pulled to GND by a resistor in shutdown.

See the High-Voltage Switch Control section for details.

5 THR

GON Falling Regulation Adjustment Pin. Connect THR to the center of a resistive voltage-divider
between LDO or OUT and GND to adjust the V

GON

falling regulation level. The actual regulation level

is 10 x V

THR

. See the High-Voltage Switch Control section for details.

6 SUPB Operational Amplifier Supply Input. Bypass SUPB to GND with a 0.1µF capacitor.

7OUTB Operational Amplifier Output

8 NEGB Operational Amplifier Inverting Input

9 POSB Operational Amplifier Noninverting Input

10 N.C. No Connection. Not internally connected.

11 LDO

5V Internal Linear Regulator Output. This regulator powers all internal circuitry except the operational
amplifier. Bypass LDO to GND with a 0.22µF or greater ceramic capacitor.

12 OUT

Internal Linear Regulator Supply Pin. OUT is the supply input of the internal 5V linear regulator.
Connect OUT directly to the output of the step-up regulator.

13 I.C. Internally Connected. Make no connection to this pin.

14 SS

Soft-Start Control Pin. Connect a capacitor between SS and GND to set the soft-start period of the
step-up regulator. See the Bootstrapping and Soft-Start section for details.

15 COMP

Error Amplifier Compensation Pin. See the Step-Up Regulator Loop Compensation section for details.

16 FREQ

Frequency-Select Pin. Connect FREQ to GND for 600kHz operation, and connect FREQ to IN for

1.2MHz operation.

17 IN

Supply Pin. Bypass IN to GND with a 1µF ceramic capacitor. Place the capacitor close to the IN pin.

18 LX

Switching Node. LX is the drain of the internal power MOSFET. Connect the inductor and the Schottky
diode to LX and minimize trace area for low EMI.

19 SHDN

Shutdown Control Pin. Pull SHDN low to turn off the step-up regulator, the operational amplifier, and
the switch control block.

20 FB

Feedback Pin. The FB regulation point is 1.24V (typ). Connect FB to the center of a resistive voltage­divider between the step-up regulator output and GND to set the step-up regulator output voltage.
Place the divider close to the FB pin.

21 PGND Power Ground

22 MODE

High-Voltage, Switch-Control Block-Mode Selection Timing-Adjustment Pin. See the High-Voltage
Switch Control section for details. MODE is high impedance when it is connected to LDO. MODE is
internally pulled down by a 1kΩ resistor during UVLO, when V

DLP

< 0.5 x V

LDO

, or in shutdown.

23 DRN

High-Voltage, Switch-Control Input. DRN is the drain of the internal high-voltage p-channel MOSFET
connected to GON.

24 SRC

High-Voltage Switch-Control Input. SRC is the source of the internal high-voltage p-channel MOSFET.

MAX8758

Typical Operating Circuit

The typical operating circuit (Figure 1) of the MAX8758
is a power-supply solution for TFT LCD panels in note­book computers. The circuit generates a +8.5V source
driver supply, and approximately +22V and -7V gate

driver supplies. The input voltage range for the IC is
from +1.8V to +5.5V, but the Figure 1 circuit is
designed to run from 2.7V to 3.6V. Table 1 lists some
selected components and Table 2 lists the contact
information of component suppliers.

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

10 ______________________________________________________________________________________

MAX8758

V

MAIN

+8.5V/300mA

TO VCOM
BACKPLANE

V

GON

+24V/20mA

FROM TCON

V

IN

+1.8V TO +5.5V

V

GOFF

-8V/20mA

IN

FREQ

SHDN

COMP

LDO

FB

LX

GND

PGND

OUT

SUPB

GON

DRN

CTL

MODE

SS

POSB

NEGB

OUTB

THR

DLP

SRC

C15

0.1µF

C1

3.3µF

6.3V

C2

3.3µF

6.3V

R4

10Ω

C6

1µF

R10

100kΩ

R3

100kΩ

C7

220pF

C8

33pF

C9

0.22µF

C10

0.022µF

C11

150pF

R9

20kΩ

D2 D3

D4

C3

4.7µF
10V

C4

4.7µF
10V

C5

4.7µF
10V

L1

4.7µH

C6

0.1µF

C17

0.1µF

C19

0.1µF

C18

0.1µF

R1
200kΩ
1%

R2

34.0kΩ
1%

C12

0.1µF

R5
100kΩ

R6
100kΩ

R8

20.0kΩ
1%

R7

51.1kΩ
1%

C13

0.033µF

C14

0.1µF

D1

Figure 1. Typical Operating Circuit

Detailed Description

The MAX8758 is designed primarily for TFT LCD panels
used in notebook computers. It contains a high-perfor­mance step-up regulator, a high-speed operational
amplifier, a logic-controlled, high-voltage switch-control
block with programmable delay, and an internal linear
regulator for bootstrapping operation. Figure 2 shows
the MAX8758 functional block diagram.

Step-Up Regulator

The step-up regulator is designed to generate the LCD
source driver supply. It employs a current-mode, fixed­frequency PWM architecture to maximize loop band­width and provide fast transient response to pulsed
loads typical of TFT LCD panel source drivers. The inter­nal oscillator offers two pin-selectable frequency options
(640kHz/1.2MHz), allowing users to optimize their
designs based on the specific application requirements.

MAX8758

Step-Up Regulator with Switch Control and

Operational Amplifier for TFT LCD

______________________________________________________________________________________ 11

SRC

GON

DLP

MODE

THR

CTL

DRN

SWITCH

CONTROL

SUPB

NEGB

OUTB

POSB

GND

PGND

STEP-UP

REGULATOR

CONTROLLER

FB

COMP

SS

LX

LINEAR

REGULATOR

AND BOOTSTRAP

V

IN

MAX8758

SHDN

FREQ

LDO

IN

Figure 2. Functional Diagram

Table 1. Component List

DESIGNATION

DESCRIPTION

C1, C2

3.3µF ±10%, 6.3V X5R ceramic capacitors
(0603)
TDK C1608X5R0J335M

C3, C4, C5

4.7µF ±20%, 10V X5R ceramic capacitors
(1206)
TDK C3216X5R1A475M

D1

3A, 30V Schottky diode (M-flat)
Toshiba CMS02 (top mark S2)

D2, D3, D4

200mA, 100V dual diodes (SOT23)
Fairchild MMBD4148SE (top mark D4)

L1

4.2µH, 1.9A inductor
Sumida CDRH6D12-4R2

MAX8758

The internal n-channel power MOSFET reduces the
number of external components. The supply rail of the
internal gate driver is bootstrapped to the internal linear
regulator output to improve the efficiency at low-input
voltages. The external-capacitor, soft-start function
effectively controls inrush currents. The output voltage
can be set from VINto 13V with an external resistive
voltage-divider.

PWM Control Block

Figure 3 is the block diagram of the step-up regulator.

The regulator controls the output voltage and the power
delivered to the output by modulating the duty cycle (D)
of the internal power MOSFET in each switching cycle.
The duty cycle of the MOSFET is approximated by:

where V

OUT

is the output voltage of the step-up regulator.

On the rising edge of the internal oscillator clock, the
controller sets a flip-flop, turning on the n-channel
MOSFET and applying the input voltage across the
inductor. The current through the inductor ramps up lin­early, storing energy in its magnetic field. A transcon­ductance error amplifier compares the FB voltage with
a 1.24V (typ) reference voltage. The error amplifier
changes the COMP voltage by charging or discharging
the COMP capacitor. The COMP voltage is compared
with a ramp, which is the sum of the current-sense sig­nal and a slope compensation signal. Once the ramp
signal exceeds the COMP voltage, the controller resets
the flip-flop and turns off the MOSFET. Since the induc­tor current is continuous, a transverse potential devel­ops across the inductor that turns on the Schottky
diode (D1 in Figure 1). The voltage across the inductor
then becomes the difference between the output volt­age and the input voltage. This discharge condition
forces the current through the inductor to ramp down,
transferring the energy stored in the magnetic field to
the output capacitor and the load. The MOSFET
remains off for the rest of the clock cycle.

Bootstrapping and Soft-Start

The MAX8758 features bootstrapping operation. In nor­mal operation, the internal linear regulator supplies
power to the internal circuitry. The input of the linear
regulator (OUT) should be directly connected to the
output of the step-up regulator. The step-up regulator is
enabled when the input voltage at OUT is above 1.75V,
SHDN is high, and the fault latch is not set.

After being enabled, the regulator starts open-loop
switching to generate the supply voltage for the linear
regulator with a controlled duty cycle. The internal ref­erence block turns on when the LDO voltage exceeds

2.7V (typ). When the reference voltage reaches regula­tion, the PWM controller and the current-limit circuit are
enabled and the step-up regulator enters soft-start.

D

VV

V

OUT IN

OUT

≈

−

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

12 ______________________________________________________________________________________

Table 2. Component Suppliers

SUPPLIER PHONE FAX WEBSITE

Fairchild Semiconductor 408-822-2000 408-822-2102 www.fairchildsemi.com

Sumida 847-545-6700 847-545-6720 www.sumida.com

TDK 847-803-6100 847-390-4405 www.component.tdk.com

Toshiba 949-455-2000 949-859-3963 www.toshiba.com/taec

Figure 3. Step-Up Regulator Block Diagram

CLOCK

OSCILLATOR

SLOPE COMP

TO FAULT LOGIC

LOGIC AND

DRIVER

ILIM

COMPARATOR

SOFT­START

PWM

COMPARATOR

FAULT

COMPARATOR

∑

1.0V

I

LIMIT

CURRENT

SENSE

ERROR AMP

LX

PGND

SS

FB

1.24V

COMP

FREQ

The soft-start timing can be adjusted with an external
capacitor connected between SS and GND. After the
step-up regulator is enabled, the SS pin is immediately
charged to 0.5V. Then the capacitor is charged at a
constant current of 4µA (typ). During this time, the SS
voltage directly controls the peak inductor current,
allowing a linear ramp from zero up to the full current
limit. The maximum load current is available after the
voltage on SS exceeds 1.5V. The soft-start capacitor is
discharged to ground when SHDN is low. The soft-start
routine minimizes inrush current and voltage overshoot
and ensures a well-defined startup behavior (see the
Step-Up Regulator Heavy Load Soft-Start waveform in
the Typical Operating Characteristics).

Fault Protection

During steady-state operation, the MAX8758 monitors the
FB voltage. If the FB voltage is below 1V (typ), the
MAX8758 activates an internal fault timer. If there is a
continuous fault for the fault-timer duration, the MAX8758
sets the fault latch, shutting down all the outputs. Once
the fault condition is removed, cycle the input voltage to
clear the fault latch and reactivate the device. The fault­detection circuit is disabled during the soft-start time.

The MAX8758 monitors the OUT voltage for undervoltage
and overvoltage conditions. If the OUT voltage is below

1.4V (typ) or above 13.5V (typ), the MAX8758 disables
the gate driver of the step-up regulator and prevents the
internal MOSFET from switching. The OUT undervoltage
and overvoltage conditions do not set the fault latch.

Thermal-Overload Protection

The thermal-overload protection prevents excessive
power dissipation from overheating the MAX8758.
When the junction temperature exceeds TJ= +160°C, a
thermal sensor immediately activates the fault protec­tion, which sets the fault latch and shuts down all the
outputs, allowing the device to cool down. Once the
device cools down by approximately 15°C, cycle the
input voltage or toggle SHDN to clear the fault latch
and restart the device.

The thermal-overload protection protects the controller
in the event of fault conditions. For continuous opera­tion, do not exceed the absolute maximum junction
temperature rating of TJ= +150°C.

Frequency Selection (FREQ)

The FREQ pin selects the switching frequency. Table 3
shows the switching frequency based on the FREQ con­nection. High-frequency (1.2MHz) operation optimizes
the application for the smallest component size, trading
off efficiency due to higher switching losses. Low-fre­quency (600kHz) operation offers the best overall efficien­cy at the expense of component size and board space.

Operational Amplifier

The MAX8758’s operational amplifier is typically used
to drive the LCD backplane (VCOM) or the gamma-cor­rection-divider string. The operational amplifier features
±150mA output short-circuit current, 7.5V/µs slew rate,
and 12MHz bandwidth. The rail-to-rail input and output
capability maximizes system flexibility.

Short-Circuit Current Limit

The operational amplifier limits short-circuit current to
approximately ±150mA if the output is directly shorted to
SUPB or to GND. If the short-circuit condition persists,
the junction temperature of the IC rises until it reaches
the thermal shutdown threshold (+160°C typ). Once the
junction temperature reaches the thermal shutdown
threshold, an internal thermal sensor immediately sets
the thermal fault latch, shutting off all the IC’s outputs.
The device remains inactive until the input voltage is
cycled or SHDN is toggled.

Driving Pure Capacitive Load

The operational amplifier is typically used to drive the
LCD backplane (VCOM) or the gamma-correction
divider string. The LCD backplane consists of a distrib­uted series capacitance and resistance, a load that can
be easily driven by the operational amplifier. However,
if the operational amplifier is used in an application with
a pure capacitive load, steps must be taken to ensure
stable operation.

As the operational amplifier’s capacitive load increases,
the amplifier’s bandwidth decreases and gain peaking
increases. A 5Ω to 50Ω small resistor placed between
OUTB and the capacitive load reduces peaking but also
reduces the gain. An alternative method of reducing
peaking is to place a series RC network (snubber) in par­allel with the capacitive load. The RC network does not
continuously load the output or reduce the gain. Typical
values of the resistor are between 100Ω and 200Ω and
the typical value of the capacitor is 10pF.

High-Voltage Switch Control

The MAX8758’s high-voltage switch-control block (Figure

5) consists of two high-voltage, p-channel MOSFETs: Q1,
between SRC and GON and Q2, between GON and
DRN. The switch-control block is enabled when V

DLP

exceeds V

LDO

/2 and then Q1 and Q2 are controlled by
CTL and MODE. There are two different modes of opera­tion (see the Typical Operating Characteristics section.)

MAX8758

Step-Up Regulator with Switch Control and

Operational Amplifier for TFT LCD

______________________________________________________________________________________ 13

Table 3. Frequency Selection

FREQ SWITCHING FREQUENCY (kHz)

GND 600

IN 1200

MAX8758

Activate the first mode by connecting MODE to LDO.
When CTL is logic high, Q1 turns on and Q2 turns off,
connecting GON to SRC. When CTL is logic low, Q1
turns off and Q2 turns on, connecting GON to DRN.
GON can then be discharged through a resistor con­nected between DRN and PGND or AVDD. Q2 turns off
and stops discharging GON when V

GON

reaches 10

times the voltage on THR.

When V

MODE

is less than 0.9 x V

LDO

, the switch control
block works in the second mode. The rising edge of
V

CTL

turns on Q1 and turns off Q2, connecting GON to
SRC. An internal n-channel MOSFET Q3 between
MODE and GND is also turned on to discharge an
external capacitor between MODE and GND. The
falling edge of V

CTL

turns off Q3, and an internal 50µA
current source starts charging the MODE capacitor.
Once V

MODE

exceeds 0.5 x V

REF

, the switch control
block turns off Q1 and turns on Q2, connecting GON to
DRN. GON can then be discharged through a resistor
connected between DRN and GND or AVDD. Q2 turns
off and stops discharging GON when V

GON

reaches 10

times the voltage on THR.

The timing of enabling the switch control block can be
adjusted with an external capacitor connected between
DLP and GND. An internal current source starts charg­ing the DLP capacitor if the input voltage is above

1.75V (typ), SHDN is high, and the fault latch is not set.
The voltage on DLP linearly rises because of the con­stant-charging current. When VDLP goes above 2.5V
(typ), the switch control block is enabled. The switch
control block is disabled and DLP is held low when the
MAX8758 is shut down or in a fault state.

Linear Regulator (LDO)

The MAX8758 includes an internal 5V linear regulator.
OUT is the input of the linear regulator and should be
directly connected to the output of the step-up regulator.
The input voltage range is between 4.5V and 13V. The
output of the linear regulator (LDO) is set to 5V (typ). The
regulator powers all the internal circuitry including the
gate driver. This feature significantly improves the effi­ciency at low input voltages. Bypass the LDO pin to
GND with a 0.22µF or greater ceramic capacitor.

Design Procedure

Step-Up Regulator

Step-Up Regulator Inductor Selection

The inductance value, peak-current rating, and series
resistance are factors to consider when selecting the
inductor. These factors influence the converter’s effi­ciency, maximum output-load capability, transient
response time, and output voltage ripple. Physical size
and cost are also important factors to be considered.

The maximum output current, input voltage, output volt­age, and switching frequency determine the inductor
value. Very high inductance values minimize the cur­rent ripple and, therefore, reduce the peak current,
which decreases core losses in the inductor and I2R
losses in the entire power path. However, large induc­tor values also require more energy storage and more
turns of wire, which increase physical size and can
increase I2R losses in the inductor. Low inductance val­ues decrease the physical size but increase the current
ripple and peak current. Finding the best inductor
involves choosing the best compromise between circuit
efficiency, inductor size, and cost.

The equations used here include a constant LIR, which
is the ratio of the inductor peak-to-peak ripple current
to the average DC inductor current at the full-load cur­rent. The best trade-off between inductor size and cir­cuit efficiency for step-up regulators generally has an
LIR between 0.3 and 0.5. However, depending on the
AC characteristics of the inductor core material and
ratio of inductor resistance to other power-path resis­tances, the best LIR can shift up or down. If the induc­tor resistance is relatively high, more ripple can be
accepted to reduce the number of turns required and
increase the wire diameter. If the inductor resistance is
relatively low, increasing inductance to lower the peak
current can decrease losses throughout the power
path. If extremely thin high-resistance inductors are
used, as is common for LCD panel applications, the
best LIR can increase to between 0.5 and 1.0.

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

14 ______________________________________________________________________________________

MAX8758

Step-Up Regulator with Switch Control and

Operational Amplifier for TFT LCD

______________________________________________________________________________________ 15

REF

DLP

MODE

CTL

FAULT
SHDN
REF_OK

0.5 x V

REF

5µA

REF

50µA

1kΩ

9R

R

Q3

Q4

Q1

Q2

SRC

GON

DRN

THR

Q5

4R

1kΩ

5R

R

Figure 4. Switch Control

MAX8758

In Figure 1’s Typical Operating Circuit, the LCD’s gate-
on and gate-off voltages are generated from two unreg­ulated charge pumps driven by the step-up regulator’s
LX node. The additional load on LX must therefore be
considered in the inductance calculation. The effective
maximum output current I

MAIN(EFF)

becomes the sum
of the maximum load current on the step-up regulator’s
output plus the contributions from the positive and neg­ative charge pumps:

I

MAIN(EFF)

= I

MAIN(MAX)

+ n

NEG

x I

NEG

+ (n

POS

+ 1) x I

POS

where I

MAIN(MAX)

is the maximum output current, n

NEG

is the number of negative charge-pump stages, n

POS

is

the number of positive charge-pump stages, I

NEG

is

the negative charge-pump output current, and I

POS

is
the positive charge-pump output current, assuming the
pump source for I

POS

is V

MAIN

.

The required inductance can then be calculated as
follows:

where VINis the typical input voltage and η

TYP

is the
expected efficiency obtained from the appropriate
curve in the Typical Operating Characteristics.

Choose an available inductor value from an appropriate
inductor family. Calculate the maximum DC input cur­rent at the minimum input voltage V

IN(MIN)

using con-

servation of energy and the expected efficiency at that
operating point (η

MIN

) taken from an appropriate curve

in the Typical Operating Characteristics:

Calculate the ripple current at that operating point and
the peak current required for the inductor:

The inductor’s saturation current rating and the guaran­teed minimum value of the MAX8758’s LX current limit
(I

LIM

) should exceed I

PEAK

and the inductor’s DC current

rating should exceed I

IN(DC,MAX)

. For good efficiency,

choose an inductor with less than 0.1Ω series resistance.

Considering the Typical Operating Circuit, the maxi­mum load current (I

MAIN(MAX)

) is 300mA for the step­up regulator, 20mA for the two-stage positive charge
pump, and 20mA for the one-stage negative charge
pump. Altogether, the effective maximum output cur­rent, I

MAIN(EFF)

is 360mA with an 8.5V output and a
typical input voltage of 3.3V. The switching frequency is
set to 1.2MHz. Choosing an LIR of 0.4 and estimating
efficiency of 85% at this operating point:

Using the circuit’s minimum input voltage (3V) and esti­mating efficiency of 80% at that operating point:

The ripple current and the peak current are:

The peak-inductor current does not exceed the guaran­teed minimum value of the LX current limit in the

Electrical Characteristics table.

Step-Up Regulator Output Capacitor Selection

The total output voltage ripple has two components: the
capacitive ripple caused by the charging and discharg­ing of the output capacitance, and the ohmic ripple due
to the capacitor’s equivalent series resistance (ESR):

V

RIPPLE

= V

RIPPLE(C)

+ V

ARIPPLE(ESR)

and

V

RIPPLE(ESR)

≈ I

PEAK

x R

ESR

where I

PEAK

is the peak inductor current (see the Step-
Up Regulator Inductor Selection section). For ceramic
capacitors, the output voltage ripple is typically dominat­ed by V

RIPPLE(C)

. The voltage rating and temperature
characteristics of the output capacitor must also be con­sidered.

V

I

C

VV

Vf

RIPPLE C

MAIN

MAIN

MAIN IN

MAIN SW

()

≈ ×

×













−

IAAA

PEAK

. . .=+≈128

04

2

148

I

VVV

HVMHz

A

RIPPLE

(. )

. . .

.=

×

××

≈

−3853

42 85 12

04

µ

I

AV

V

A

IN DC MAX(, )

. .

.

.=

×

×

≈

036 85

308

128

L

V
V

VV

A MHz

H

.
.

. .

. .

.

.

.=











×

−

×











×











≈

33
85

85 33

036 12

085

04

42

2

µ

II

I

PEAK IN DC MAX

RIPPLE

(, )

=+

2

I

VVV

LV f

RIPPLE

IN MIN MAIN IN MIN

MAIN OSC

() ()

=

×

()

××

−

I

IV

V

IN DCMAX

MAIN EFF MAIN

IN MIN MIN

(, )

()

()

=

×

× η

L

V

V

VV

IfLIR

IN

MAIN

MAIN IN

MAIN EFF OSC

TYP

()

=













×

×













×











−

2

η

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

16 ______________________________________________________________________________________

Step-Up Regulator Input Capacitor Selection

The input capacitor reduces the current peaks drawn
from the input supply and reduces noise injection into
the IC. Two 10µF ceramic capacitors are used in the
Typical Applications Circuit (Figure 1) because of the
high source impedance seen in typical lab setups.
Actual applications usually have much lower source
impedance since the step-up regulator often runs
directly from the output of another regulated supply.
Typically, the input capacitance can be reduced below
the values used in the Typical Applications Circuit.

Step-Up Regulator Rectifier Diode

The MAX8758’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommend­ed for most applications because of their fast recovery
time and low forward voltage. In general, a 2A Schottky
diode complements the internal MOSFET well.

Step-Up Regulator Output Voltage Selection

The output voltage of the step-up regulator can be
adjusted by connecting a resistive voltage-divider from
the output (V

OUT

) to GND with the center tap connect-

ed to FB (see Figure 1). Select R2 in the 10kΩ to 50kΩ
range. Calculate R1 with the following equation:

where VFB, the step-up regulator’s feedback set point,
is 1.25V. Place R1 and R2 close to the IC.

Step-Up Regulator Loop Compensation

Choose R

COMP

(R3 in Figure 1) to set the high-frequen­cy integrator gain for fast transient response. Choose
C

COMP

(C7 in Figure 1) to set the integrator zero to

maintain loop stability.

For low-ESR output capacitors, use the following equa­tions to obtain stable performance and good transient
response:

To further optimize transient response, vary R

COMP

in

20% steps and C

COMP

in 50% steps while observing

transient-response waveforms.

Place C

COMP2

(C8 in Figure 1) from COMP to GND to

add an additional high-frequency pole. UseC

COMP2

between 10pF and 47pF.

Step-Up Regulator Soft-Start Capacitor

The soft-start capacitor should be large enough that it
does not reach final value before the output has
reached regulation. Calculate the soft-start capacitor
(CSS) value using:

where C

MAIN

is the total output capacitance, V

MAIN

is

the maximum output voltage, and I

INRUSH

is the peak

inrush current allowed, I

MAIN

is the maximum output

current, and VINis the minimum input voltage.

The load must wait for the soft-start cycle to finish
before drawing a significant amount of load current.
The duration after which the load can begin to draw
maximum load current is:

t

MAX

= 6.77 x 105x C

SS

Charge Pumps

Selecting the Number of Charge-Pump Stages

For highest efficiency, always choose the lowest num­ber of charge-pump stages that meet the output volt­age requirement.

The number of positive charge-pump stages is given by:

where n

POS

is the number of positive-charge-pump

stages, V

GON

is the positive-charge-pump output,

V

MAIN

is the main step-up regulator output, and VDis

the forward voltage drop of the charge-pump diode.

The number of negative charge-pump stages is given by:

where n

NEG

is the number of negative-charge-pump

stages, V

GOFF

is the negative charge-pump output,

V

MAIN

is the main step-up regulator output, and VDis

the forward voltage drop of the charge-pump diode.

n

V

VV

NEG

GOFF

MAIN D

=×

−

−

2

n

VV

VV

POS

GON MAIN

MAIN D

=×

−

−

2

CC

VVV

VI I V

SS MAIN

MAIN

IN MAIN

IN INRUSH MAIN MAIN

=× ×

×

×

××













−

−

−

21 10

6

2

C

VC
IR

COMP

MAIN MAIN

MAIN MAX COMP

()

≈

×

××10

R

VV C

LI

COMP

IN MAIN MAIN

MAIN MAX

()

≈

×× ×

×

315

RR

V

V

MAIN

FB

12 1 =×













−

MAX8758

Step-Up Regulator with Switch Control and

Operational Amplifier for TFT LCD

______________________________________________________________________________________ 17

MAX8758

Charge-Pump Flying Capacitors

Increasing the flying capacitor (C6, C17, C18) value
lowers the effective source impedance and increases
the output-current capability. Increasing the capaci­tance indefinitely has a negligible effect on output-cur­rent capability because the diode impedance places a
lower limit on the source impedance. Ceramic capaci­tors of 0.1µF or greater work well in most applications
that require output currents in the order of 10mA to
20mA.

The flying capacitor’s voltage rating must exceed the
following:

VC> n x V

MAIN

where n is the stage number in which the flying capaci­tor appears, and V

MAIN

is the output voltage of the

main step-up regulator.

Charge-Pump Output Capacitor

Increasing the output capacitance or decreasing the
ESR reduces the output voltage ripple and the peak-to­peak voltage during load transients. With ceramic
capacitors, the output voltage ripple is dominated by
the capacitance value. Use the following equation to
approximate the required capacitor value:

where C

MAIN_CP

is the output capacitor of the charge

pump, I

LOAD_CP

is the load current of the charge

pump, and V

RIPPLE_CP

is the peak-to-peak value of the

output ripple.

The charge-pump output capacitor is typically also the
input capacitor for a linear regulator. Often, its value must
be increased to maintain the linear regulator’s stability.

Charge-Pump Rectifier Diodes

Use low-cost, silicon-switching diodes with a current
rating equal to or greater than two times the average
charge-pump input current. If it helps avoid an extra
stage, some or all of the diodes can be replaced with
Schottky diodes with equivalent current ratings.

PC Board Layout and Grounding

Careful PC board layout is important for proper operation.
Use the following guidelines for good PC board layout:

1) Minimize the area of high-current loops by placing
the step-up regulator’s inductor, diode, and output
capacitors near its input capacitors, its LX, and
PGND pin. The high-current input loop goes from

the positive terminal of the input capacitor to the
inductor, to the IC’s LX pin, out of PGND, and to
the input capacitor’s negative terminal. The high­current output loop is from the positive terminal of
the input capacitor to the inductor, to the output
diode (D1), to the positive terminal of the output
capacitors, reconnecting between the output
capacitor and input capacitor ground terminals.
Connect these loop components with short, wide
connections. Avoid using vias in the high-current
paths. If vias are unavoidable, use many vias in
parallel to reduce resistance and inductance.

2) Create a power ground island (PGND) for the
step-up regulator, consisting of the input and out­put capacitor grounds and the PGND pin.
Maximizing the width of the power ground traces
improves efficiency and reduces output voltage
ripple and noise spikes. Create an analog ground
plane (GND) consisting of the GND pin, the feed­back-divider ground connection, the COMP and
DLP capacitor ground connections, and the
device’s exposed backside pad. Connect the
PGND and GND islands by connecting the two
ground pins directly to the exposed backside pad.
Make no other connections between these sepa­rate ground planes.

3) Place the feedback voltage-divider resistors as
close to the feedback pin as possible. The
divider’s center trace should be kept short.
Placing the resistors far away causes the FB trace
to become antennas that can pick up switching
noise. Care should be taken to avoid running the
feedback trace near LX.

4) Place the IN pin bypass capacitor as close to the
device as possible. The ground connection of the
IN bypass capacitor should be connected directly
to the GND pin with a wide trace.

5) Minimize the length and maximize the width of the
traces between the output capacitors and the load
for best transient responses.

6) Minimize the size of the LX node while keeping it
wide and short. Keep the LX node away from
feedback node (FB) and analog ground. Use DC
traces as shield if necessary.

Refer to the MAX8758 evaluation kit for an example of
proper board layout.

C

I

fV

MAIN CP

LOAD CP

OSC RIPPLE CP

_

_

_

≥

××2

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

18 ______________________________________________________________________________________

MAX8758

Step-Up Regulator with Switch Control and

Operational Amplifier for TFT LCD

______________________________________________________________________________________ 19

Chip Information

TRANSISTOR COUNT: 3208

PROCESS: BiCMOS

Pin Configuration

MAX8758

TOP VIEW

2

GON

1

GND

3

CTL

4

DLP5THR

6

SUPB

24

SRC

23

DRN

22

MODE

21

PGND

20

FB

19

SHDN

18LX17IN16

FREQ15COMP14SS13I.C.

11

LDO

10

N.C.

12

OUT

9

POSB

8

NEGB

7

OUTB

MAX8758

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

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages

.)

QFN THIN.EPS

D2

(ND-1) X e

e

D

C

PIN # 1
I.D.

(NE-1) X e

E/2

E

0.08 C

0.10 C

A

A1

A3

DETAIL A

E2/2

E2

0.10 M C A B

PIN # 1 I.D.

b

0.35x45°

D/2

D2/2

L

C

L

C

e e

L

CC

L

k

LL

DETAIL B

L

L1

e

XXXXX

MARKING

H

1

2

21-0140

PACKAGE OUTLINE,
16, 20, 28, 32, 40L THIN QFN, 5x5x0.8mm

-DRAWING NOT TO SCALE-

L

e/2

COMMON DIMENSIONS

3.353.15T2855-1 3.25 3.353.15 3.25

MAX.

3.20

EXPOSED PAD VARIATIONS

3.00T2055-2 3.10

D2

NOM.MIN.

3.203.00 3.10

MIN.E2NOM. MAX.

NE

ND

PKG.

CODES

1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994.

2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES.

3. N IS THE TOTAL NUMBER OF TERMINALS.

4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL
CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE
OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1
IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE.

5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN

0.25 mm AND 0.30 mm FROM TERMINAL TIP.

6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY.

7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION.

8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.

9. DRAWING CONFORMS TO JEDEC MO220, EXCEPT EXPOSED PAD DIMENSION FOR T2855-1,
T2855-3, AND T2855-6.

NOTES:

SYMBOL

PKG.

N

L1

e

E

D

b

A3

A

A1

k

10. WARPAGE SHALL NOT EXCEED 0.10 mm.

JEDEC

T1655-1 3.203.00 3.10 3.00 3.10 3.20

0.70 0.800.75

4.90

4.90

0.25

0.250--

4

WHHB

4

16

0.350.30

5.10

5.105.00

0.80 BSC.

5.00

0.05

0.20 REF.

0.02

MIN. MAX.NOM.

16L 5x5

3.10

T3255-2

3.00

3.20

3.00 3.10 3.20

2.70

T2855-2 2.60 2.602.80 2.70 2.80

L

0.30 0.500.40

---

---

WHHC

20

5

5

5.00

5.00

0.30

0.55

0.65 BSC.

0.45

0.25

4.90

4.90

0.25

0.65

--

5.10

5.10

0.35

20L 5x5

0.20 REF.

0.75

0.02

NOM.

0

0.70

MIN.

0.05

0.80

MAX.

---

WHHD-1

28

7

7

5.00

5.00

0.25

0.55

0.50 BSC.

0.45

0.25

4.90

4.90

0.20

0.65

--

5.10

5.10

0.30

28L 5x5

0.20 REF.

0.75

0.02

NOM.

0

0.70

MIN.

0.05

0.80

MAX.

---

WHHD-2

32

8

8

5.00

5.00

0.40

0.50 BSC.

0.30

0.25

4.90

4.90

0.50

--

5.10

5.10

32L 5x5

0.20 REF.

0.75

0.02

NOM.

0

0.70

MIN.

0.05

0.80

MAX.

0.20 0.25 0.30

DOWN
BONDS
ALLOWED

NO

YES3.103.00 3.203.103.00 3.20T2055-3

3.103.00 3.203.103.00 3.20T2055-4

T2855-3 3.15 3.25 3.35 3.15 3.25 3.35

T2855-6 3.15 3.25 3.35 3.15 3.25 3.35

T2855-4 2.60 2.70 2.80 2.60 2.70 2.80

T2855-5 2.60 2.70 2.80 2.60 2.70 2.80

T2855-7 2.60 2.70

2.80

2.60 2.70 2.80

3.203.00 3.10T3255-3 3.203.00 3.10

3.203.00 3.10T3255-4 3.203.00 3.10

NO

NO
NO

NO

NO

NO

NO

NO

YES
YES

YES

YES

3.203.00T1655-2 3.10 3.00 3.10 3.20 YES
NO3.203.103.003.10T1655N-1 3.00 3.20

3.353.15T2055-5 3.25 3.15 3.25 3.35

YES

3.35

3.15T2855N-1 3.25 3.15 3.25 3.35

NO

3.35

3.15T2855-8 3.25 3.15 3.25 3.35

YES

3.203.10T3255N-1 3.00

NO

3.203.103.00

L

0.40

0.40

**

**
**
**

**

**

**
**
**
**

**

**
**

**
**
**

**

**

**

SEE COMMON DIMENSIONS TABLE

±0.15

11. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY.

H

2

2

21-0140

PACKAGE OUTLINE,
16, 20, 28, 32, 40L THIN QFN, 5x5x0.8mm

-DRAWING NOT TO SCALE-

12. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY.

3.30T4055-1 3.20 3.40 3.20 3.30 3.40

**

YES

0.0500.02

0.600.40 0.50

10

-----

0.30

40
10

0.40 0.50

5.10

4.90 5.00

0.25 0.35 0.45

0.40 BSC.

0.15

4.90

0.250.20

5.00 5.10

0.20 REF.

0.70

MIN.

0.75 0.80

NOM.

40L 5x5

MAX.

13. LEAD CENTERLINES TO BE AT TRUE POSITION AS DEFINED BY BASIC DIMENSION "e", ±0.05.