Datasheet

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General Description

The MAX1518B includes a high-performance step-up

regulator, two linear-regulator controllers, and high-cur-

rent operational amplifiers for active-matrix, thin-film tran-

sistor (TFT), liquid-crystal displays (LCDs). Also included

is a logic-controlled, high-voltage switch with adjustable

delay.

The step-up DC-DC converter provides the regulated

supply voltage for the panel source driver ICs. The con-

verter is a high-frequency (1.2MHz) current-mode regu-

lator with an integrated 14V n-channel MOSFET that

allows the use of ultra-small inductors and ceramic

capacitors. It provides fast transient response to pulsed

loads while achieving efficiencies over 85%.

The gate-on and gate-off linear-regulator controllers

provide regulated TFT gate-on and gate-off supplies

using external charge pumps attached to the switching

node. The MAX1518B includes five high-performance

operational amplifiers. These amplifiers are designed to

drive the LCD backplane (VCOM) and/or the gamma-

correction divider string. The device featureS high out-

put current (±150mA), fast slew rate (13V/µs), wide

bandwidth (12MHz), and rail-to-rail inputs and outputs.

The MAX1518B is available in a 32-pin thin QFN pack-

age with a maximum thickness of 0.8mm for ultra-thin

LCD panels.

Applications

Notebook Computer Displays

LCD Monitor Panels

Automotive Displays

Features

♦ 2.6V to 6.5V Input Supply Range

♦ 1.2MHz Current-Mode Step-Up Regulator

Fast Transient Response to Pulsed Load

High-Accuracy Output Voltage (1.5%)

Built-In 14V, 2.4A, 0.16Ω n-Channel MOSFET

High Efficiency (90%)

♦ Linear-Regulator Controllers for V

GON

and V

GOFF

♦ High-Performance Operational Amplifiers

±150mA Output Short-Circuit Current

13V/µs Slew Rate

12MHz, -3dB Bandwidth

Rail-to-Rail Inputs/Outputs

♦ Logic-Controlled, High-Voltage Switch with

Adjustable Delay

♦ Timer-Delay Fault Latch for All Regulator Outputs

♦ Thermal-Overload Protection

♦ 0.6mA Quiescent Current

MAX1518B

TFT-LCD DC-DC Converter with

Operational Amplifiers

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

STEP-UP

CONTROLLER

GATE-ON

CONTROLLER

SWITCH

CONTROL

GATE-OFF

CONTROLLER

REF

MAIN

PGND

AGND

DRVP

FBP

GON

GOFF

DEL

CTL

DRVN

FBN

NEG4

REF

POS4

NEG5

POS5

OUT4

OUT5

BGND

NEG2

POS2

OP3

POS3

OUT2

OUT3

POS1

OUT1

NEG1

SUP

COM

DRN

SRC

COMP

MAX1518B

OP2

OP1

OP5

OP4

Minimal Operating Circuit

19-3244; Rev 0; 10/05

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.

EVALUATION KIT

AVAILABLE

PART

TEMP

RANGE

PIN-PACKAGE

PKG

CODE

MAX1518BETJ

-40°C to

+100°C

32 Thi n QFN 5m m x 5m m

T3255-4

Pin Configuration appears at end of data sheet.

Summary of content (25 pages)

PAGE 1
9-3244; Rev 0; 10/05 KIT ATION EVALU E L B A AVAIL TFT-LCD DC-DC Converter with Operational Amplifiers The MAX1518B includes a high-performance step-up regulator, two linear-regulator controllers, and high-current operational amplifiers for active-matrix, thin-film transistor (TFT), liquid-crystal displays (LCDs). Also included is a logic-controlled, high-voltage switch with adjustable delay. The step-up DC-DC converter provides the regulated supply voltage for the panel source driver ICs.
PAGE 2
MAX1518B TFT-LCD DC-DC Converter with Operational Amplifiers ABSOLUTE MAXIMUM RATINGS IN, CTL to AGND ......................................................-0.3V to +7V COMP, FB, FBP, FBN, DEL, REF to AGND ....-0.3V to (VIN + 0.3V) PGND, BGND to AGND ......................................................±0.3V LX to PGND ............................................................-0.3V to +14V SUP to AGND .........................................................-0.3V to +14V DRVP, SRC to AGND...............
PAGE 3
TFT-LCD DC-DC Converter with Operational Amplifiers (VIN = 3V, VSUP = 8V, PGND = AGND = BGND = 0, IREF = 25µA, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER LX On-Resistance SYMBOL CONDITIONS MIN RLX(ON) LX Leakage Current ILX VLX = 13V LX Current Limit ILIM VFB = 1V, duty cycle = 65% Current-Sense Transconductance Soft-Start Period TYP MAX UNITS 160 250 mΩ 0.02 40 µA 2.5 3.0 3.5 A 3.0 3.8 5.
PAGE 4
MAX1518B TFT-LCD DC-DC Converter with Operational Amplifiers ELECTRICAL CHARACTERISTICS (continued) (VIN = 3V, VSUP = 8V, PGND = AGND = BGND = 0, IREF = 25µA, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) FBP Line (IN) Regulation Error DRVP Sink Current IDRVP = 100µA, 2.6V < VIN < 5.5V IDRVP DRVP Off-Leakage Current Soft-Start Period VFBP = 1.1V, VDRVP = 10V ±1.5 1 VFBP = 1.4V, VDRVP = 28V 0.
PAGE 5
TFT-LCD DC-DC Converter with Operational Amplifiers (VIN = 3V, VSUP = 8V, PGND = AGND = BGND = 0, IREF = 25µA, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER IN Supply Range SYMBOL CONDITIONS VIN IN Undervoltage-Lockout Threshold VUVLO VIN rising, typical hysteresis = 150mV MIN MAX UNITS 2.6 5.5 V 2.250 2.715 V VFB = VFBP = 1.4V, VFBN = 0, LX not switching IN Quiescent Current IIN REF Output Voltage 0.8 mA VFB = 1.1V, VFBP = 1.
PAGE 6
MAX1518B TFT-LCD DC-DC Converter with Operational Amplifiers ELECTRICAL CHARACTERISTICS (continued) (VIN = 3V, VSUP = 8V, PGND = AGND = BGND = 0, IREF = 25µA, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) FBP Effective Load-Regulation Error (Transconductance) VDRVP = 10V, IDRVP = 50µA to 1mA -2 % FBP Line (IN) Regulation Error IDRVP = 100µA, 2.6V < VIN < 5.5V 5 mV DRVP Sink Current IDRVP VFBP = 1.
PAGE 7
TFT-LCD DC-DC Converter with Operational Amplifiers 70 60 50 40 1.3 NO LOAD, SUP DISCONNECTED, R1 = 95.3kΩ, R2 = 10.2kΩ 8 1.2 CURRENT INTO INDUCTOR 6 4 1.1 MAX1518B toc03 MAX1518B toc02 10 SUPPLY CURRENT (mA) VIN = 3.3V 1.4 SWITCHING FREQUENCY (MHz) VIN = 5.0V 80 CURRENT INTO IN PIN 2 VOUT = 13V 0 1.0 30 100 1000 2.5 3.0 3.5 4.0 4.5 5.0 2.5 5.5 3.0 3.5 4.0 4.5 5.0 5.
PAGE 8
Typical Operating Characteristics (continued) (Circuit of Figure 1. VIN = 5V, VMAIN = 13V, VGON = 24V, VGOFF = -8V, VOUT1 = VOUT2 = VOUT3 = VOUT4 = VOUT5 = 6.5V, TA = +25°C unless otherwise noted.) GATE-ON REGULATOR LOAD REGULATION -0.2 -0.4 -0.6 VGON = 23.5V IGON = 20mA -0.8 -0.10 -0.15 -0.20 -0.30 24 25 26 27 28 0 5 INPUT VOLTAGE (V) 0.50 0.
PAGE 9
TFT-LCD DC-DC Converter with Operational Amplifiers OPERATIONAL-AMPLIFIER LARGE-SIGNAL STEP RESPONSE OPERATIONAL-AMPLIFIER LOAD-TRANSIENT RESPONSE OPERATIONAL-AMPLIFIER SMALL-SIGNAL STEP RESPONSE MAX1518B toc16 MAX1518B toc15 MAX1518B toc17 VSUP = 6V 0V A A A 0V +50mA B 0 0V B B -50mA 0V 1µs/div 400ns/div A: OUTPUT VOLTAGE, 1V/div, AC-COUPLED B: OUTPUT CURRENT, 50mA/div 0V 400ns/div A: INPUT SIGNAL, 2V/div B: OUTPUT SIGNAL, 2V/div A: INPUT SIGNAL, 100mV/div B: OUTPUT SIGNAL, 100mV/div Pin D
PAGE 10
TFT-LCD DC-DC Converter with Operational Amplifiers MAX1518B Pin Description (continued) PIN NAME 17 OUT4 Operational-Amplifier 4 Output 18 POS5 Operational-Amplifier 5 Noninverting Input 19 NEG5 Operational-Amplifier 5 Inverting Input 20 OUT5 Operational-Amplifier 5 Output 21 LX n-Channel Power MOSFET Drain and Switching Node. Connect the inductor and Schottky diode to LX and minimize the trace area for lowest EMI. 22 IN Supply Voltage Input. IN can range from 2.6V to 6.5V.
PAGE 11
TFT-LCD DC-DC Converter with Operational Amplifiers The MAX1518B Typical Operating Circuit (Figure 1) is a complete power-supply system for TFT LCDs. The circuit generates a +13V source-driver supply and +24V and -8V gate-driver supplies. The input voltage range for the IC is from +2.6V to +6.5V. The listed load currents in Figure 1 are available from a +4.5V to +5.5V supply. Table 1 lists some recommended components, and Table 2 lists the contact information of component suppliers. Table 1.
PAGE 12
MAX1518B TFT-LCD DC-DC Converter with Operational Amplifiers LX L1 3.0µH VIN 4.5V TO 5.5V D1 C2 22µF C1 22µF R10 10Ω R1 95.3kΩ 1% LX IN FB C18 0.1µF LX R1 10.2kΩ 1% 180kΩ 0.1µF AGND COMP PGND 220µF 0.1µF D2 LX 0.1µF MAX1518B 6.8kΩ D3 6.8kΩ DRVP 0.1µF Q2 R7 332kΩ 1% VGOFF -8V/50mA DRVN R4 192kΩ 1% Q1 FBP R5 10.0kΩ 1% FBN 0.22µF R8 40.2kΩ 1% 0.47µF SRC REF VGON 24V/20mA COM 0.22µF DRN DEL CTL 0.033µF SUP 0.
PAGE 13
TFT-LCD DC-DC Converter with Operational Amplifiers MAX1518B VCN VCP VIN VMAIN LX IN FB STEP-UP CONTROLLER PGND COMP AGND VCP MAX1518B DRVP GATE-ON CONTROLLER FBP VGON SRC DEL COM SWITCH CONTROL CTL VCN DRN DRVN GATE-OFF CONTROLLER VGOFF SUP NEG1 OUT1 FBN OP1 REF POS1 NEG2 OUT2 REF NEG4 OP2 OP4 POS2 OUT4 POS4 NEG5 OUT3 OP3 OP5 POS3 OUT5 POS5 BGND Figure 2.
PAGE 14
MAX1518B TFT-LCD DC-DC Converter with Operational Amplifiers LX RESET DOMINANT CLOCK S R PGND Q ILIM COMPARATOR SOFTSTART VLIMIT SLOPE COMP PWM COMPARATOR Σ CURRENT SENSE OSCILLATOR FAULT COMPARATOR TO FAULT LATCH 1.0V ERROR AMP FB 1.236V COMP Figure 3. Step-Up Regulator Functional Diagram This discharge condition forces the current through the inductor to ramp back down, transferring the energy stored in the magnetic field to the output capacitor and the load.
PAGE 15
TFT-LCD DC-DC Converter with Operational Amplifiers MAX1518B LX FROM CHARGE-PUMP OUTPUT VMAIN 0.1µF VMAIN 13V 0.1µF DRVP NPN CASCODE TRANSISTOR PNP PASS TRANSISTOR 6.8kΩ VGON MAX1518B Q1 DRVP MAX1518B VGON 35V 0.47µF 0.22µF 267kΩ 1% FBP FBP 10.0kΩ 1% Figure 4. Using Cascoded npn for Charge-Pump Output Voltages > 28V Figure 5. The linear regulator controls the intermediate chargepump stage. Gate-Off Linear-Regulator Controller, REG N SUP or to BGND.
PAGE 16
MAX1518B TFT-LCD DC-DC Converter with Operational Amplifiers Undervoltage Lockout (UVLO) The undervoltage-lockout (UVLO) circuit compares the input voltage at IN with the UVLO threshold (2.5V rising, 2.30V falling, typ) to ensure the input voltage is high enough for reliable operation. The 200mV (typ) hysteresis prevents supply transients from causing a restart. Once the input voltage exceeds the UVLO rising threshold, startup begins.
PAGE 17
TFT-LCD DC-DC Converter with Operational Amplifiers MAX1518B IN MAX1518B 5µA 2.5V FB OK FBP OK FBN OK Q1 SRC DEL REF COM CTL Q2 DRN Figure 7. Switch-Control Block Fault Protection Thermal-Overload Protection During steady-state operation, if the output of the main regulator or any of the linear-regulator outputs does not exceed its respective fault-detection threshold, the MAX1518B activates an internal fault timer.
PAGE 18
MAX1518B TFT-LCD DC-DC Converter with Operational Amplifiers Design Procedure Main Step-Up Regulator Inductor Selection The minimum 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. Size and cost are also important factors to consider.
PAGE 19
TFT-LCD DC-DC Converter with Operational Amplifiers VRIPPLE = VRIPPLE(C) + VRIPPLE(ESR) V I −V  VRIPPLE(C) ≈ MAIN  MAIN IN  , and COUT  VMAINfOSC  VRIPPLE(ESR) ≈ IPEAKRESR(COUT) where I PEAK is the peak inductor current (see the Inductor Selection section). For ceramic capacitors, the output voltage ripple is typically dominated by VRIPPLE(C). The voltage rating and temperature characteristics of the output capacitor must also be considered.
PAGE 20
MAX1518B TFT-LCD DC-DC Converter with Operational Amplifiers VMAIN >13V VIN LX has a negligible effect on output-current capability because the internal switch resistance and the diode impedance place a lower limit on the source impedance. A 0.1µF ceramic capacitor works well in most low-current applications. The flying capacitor’s voltage rating must exceed the following: FB VCX > n × VMAIN STEP-UP CONTROLLER PGND MAX1518B Figure 8.
PAGE 21
TFT-LCD DC-DC Converter with Operational Amplifiers MAX1518B POSITIVE CHARGE-PUMP OUTPUT VOLTAGE vs. VMAIN NEGATIVE CHARGE-PUMP OUTPUT VOLTAGE vs. VMAIN 60 -0 VD = 0.3V TO 1V 3-STAGE CHARGE PUMP 1-STAGE CHARGE PUMP -5 50 -10 -15 G_OFF (V) G_ON (V) 40 2-STAGE CHARGE PUMP 30 20 -20 2-STAGE CHARGE PUMP -25 -30 3-STAGE CHARGE PUMP -35 10 -40 1-STAGE CHARGE PUMP 0 VD = 0.3V TO 1V -45 2 4 6 8 10 12 14 VMAIN (V) 2 4 6 8 10 12 14 VMAIN (V) Figure 9.
PAGE 22
MAX1518B TFT-LCD DC-DC Converter with Operational Amplifiers The transconductance amplifier regulates the output voltage by controlling the pass transistor’s base current. The total DC loop gain is approximately:  10    I ×h  A V _ LR ≅   × 1+  BIAS FE   × VREF  VT    ILOAD _ LR   where VT is 26mV at room temperature, and IBIAS is the current through the base-to-emitter resistor (RBE).
PAGE 23
TFT-LCD DC-DC Converter with Operational Amplifiers Power Dissipation An IC’s maximum power dissipation depends on the thermal resistance from the die to the ambient environment and the ambient temperature. The thermal resistance depends on the IC package, PC board copper area, other thermal mass, and airflow. The MAX1518B, with its exposed backside pad soldered to 1in 2 of PC board copper, can dissipate approximately 1.7W into +70°C still air.
PAGE 24
TFT-LCD DC-DC Converter with Operational Amplifiers COM DRN CTL DEL DRVN FBN DRVP FBP TOP VIEW 32 31 30 29 28 27 26 25 SRC 1 24 COMP REF 2 23 FB AGND 3 22 IN PGND 4 21 LX OUT1 5 20 OUT5 NEG1 6 19 NEG5 POS1 7 18 POS5 OUT2 8 17 OUT4 9 10 11 12 13 14 15 16 POS2 BGND POS3 OUT3 SUP POS4 NEG4 MAX1518B NEG2 MAX1518B Pin Configuration THIN QFN 5mm x 5mm 24 ______________________________________________________________________________________
PAGE 25
TFT-LCD DC-DC Converter with Operational Amplifiers QFN THIN.EPS 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.