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Multi-Output Power Supplies with VCOM Amplifier

and High-Voltage Gamma Reference for LCD TVs

MAX17126/MAX17126A

General Description

The MAX17126/MAX17126A generate all the supply rails

for thin-film transistor liquid-crystal display (TFT LCD)

TV panels operating from a regulated 12V input. They

include a step-down and a step-up regulator, a positive

and a negative charge pump, an operational amplifier,

a high-accuracy high-voltage gamma reference, and

a high-voltage switch control block. The MAX17126/

MAX17126A can operate from input voltages from 8V

to 16.5V and is optimized for an LCD TV panel running

directly from 12V supplies.

The step-up and step-down switching regulators feature

internal power MOSFETs and high-frequency opera-

tion allowing the use of small inductors and capacitors,

resulting in a compact solution. The step-up regulator

provides TFT source driver supply voltage, while the

step-down regulator provides the system with logic sup-

ply voltage. Both regulators use fixed-frequency current-

mode control architectures, providing fast load-transient

response and easy compensation. A current-limit func-

tion for internal switches and output-fault shutdown pro-

tects the step-up and step-down power supplies against

fault conditions. The MAX17126/MAX17126A provide

soft-start functions to limit inrush current during startup.

In addition, the MAX17126/MAX17126A integrate a con-

trol block that can drive an external p-channel MOSFET

to sequence power to source drivers.

The positive and negative charge-pump regulators pro-

vide TFT gate-driver supply voltages. Both output volt-

ages can be adjusted with external resistive voltage-

dividers. A logic-controlled, high-voltage switch block

allows the manipulation of the positive gate-driver supply.

The MAX17126/MAX17126A include one high-current

operational amplifier designed to drive the LCD back-

plane (VCOM). The amplifier features high output cur-

rent (Q200mA), fast slew rate (45V/Fs), wide bandwidth

(20MHz), and rail-to-rail outputs.

Also featured in the MAX17126/MAX17126A is a high-

accuracy, high-voltage adjustable reference for gamma

correction.

The MAX17126/MAX17126A are available in a small (7mm

x 7mm), ultra-thin (0.8mm), 48-pin thin QFN package and

operate over the -40NC to +85NC temperature range.

Applications

LCD TV Panels

Features

S 8.0V to 16.5V IN Supply-Voltage Range

S Selectable Frequency (500kHz/750kHz)

S Current-Mode Step-Up Regulator

Fast Load-Transient Response

High-Accuracy Output Voltage (1.0%)

Built-In 20V, 4.2A, 100mI MOSFET

High Efficiency

Adjustable Soft-Start

Adjustable Current Limit

Low Duty-Cycle Operation (13.2V

- 13.5V AVDD)

S Current-Mode Step-Down Regulator

Fast Load-Transient Response

Built-In 20V, 3.2A, 100mI MOSFET

High Efficiency

3ms Internal Soft-Start

S Adjustable Positive Charge-Pump Regulator

S Adjustable Negative Charge-Pump Regulator

S Integrated High-Voltage Switch with Adjustable

Turn-On Delay

S High-Speed Operational Amplifier

Q200mA Short-Circuit Current

45V/µs Slew Rate

S High-Accuracy Reference for Gamma Buffer

Q1% Feedback Voltage

Up to 30mA Load Current

Low-Dropout Voltage 0.5V at 60mA

S External p-Channel Gate Control for AVDD

Sequencing

S PGOOD Comparator

S Input Undervoltage Lockout and Thermal-

Overload Protection

S 48-Pin, 7mm x 7mm, Thin QFN Package

19-4681; Rev 1; 3/10

Pin Configuration appears at end of data sheet.

+Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

Ordering Information

EVALUATION KIT

AVAILABLE

PART TEMP RANGE PIN-PACKAGE

MAX17126ETM+

-40NC to +85NC

48 Thin QFN-EP*

MAX17126AETM+

-40NC to +85NC

48 Thin QFN-EP*

Summary of content (34 pages)

PAGE 1
TION KIT EVALUA BLE IL AVA A 19-4681; Rev 1; 3/10 Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs The MAX17126/MAX17126A generate all the supply rails for thin-film transistor liquid-crystal display (TFT LCD) TV panels operating from a regulated 12V input. They include a step-down and a step-up regulator, a positive and a negative charge pump, an operational amplifier, a high-accuracy high-voltage gamma reference, and a high-voltage switch control block.
PAGE 2
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs ABSOLUTE MAXIMUM RATINGS INVL, IN2, VOP, EN, FSEL to GND........................-0.3V to +24V PGND, OGND, CPGND to GND...........................-0.3V to +0.3V DLY1, GVOFF, THR, VL to GND...........................-0.3V to +7.5V REF, FBP, FBN, FB1, FB2, COMP, SS, CLIM, PGOOD, VDET, VREF_FB, OUT to GND.........-0.3V, (VL+ 0.3) GD, GD_I to GND...................................................-0.
PAGE 3
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs (Circuit of Figure 1, VINVL= VIN2 = 12V, VVOP = VVREF_I = 15V, TA = 0°C to +85°C. Typical values are at TA = +25NC, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP 3.3 MAX UNITS STEP-DOWN REGULATOR OUT Voltage in Fixed Mode FB2 = GND, no load (Note 1) 0°C < TA = +85°C 3.25 TA = +25°C 3.267 FB2 Voltage in Adjustable Mode VOUT = 2.5V, no load (Note 1) 0°C < TA = +85°C TA = +25°C 1.23 1.2375 1.
PAGE 4
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VINVL= VIN2 = 12V, VVOP = VVREF_I = 15V, TA = 0°C to +85°C. Typical values are at TA = +25NC, unless otherwise noted.) PARAMETER LX1 Current Limit CLIM Voltage MIN TYP MAX VFB1 = 1.1V, RCLIM = unconnected CONDITIONS 3.6 4.2 4.8 VFB1 = 1.1V, with RCLIM at CLIM pin -20% 4.2 (68k/ RCLIM) +20% RCLIM = 60.5kI 0.56 0.625 0.
PAGE 5
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs (Circuit of Figure 1, VINVL= VIN2 = 12V, VVOP = VVREF_I = 15V, TA = 0°C to +85°C. Typical values are at TA = +25NC, unless otherwise noted.) PARAMETER VOP Overvoltage Fault Threshold VOP Supply Current Input Offset Voltage Input Bias Current CONDITIONS VVOP = rising, hysteresis = 200mV (Note 2) MIN TYP MAX UNITS 20.
PAGE 6
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VINVL= VIN2 = 12V, VVOP = VVREF_I = 15V, TA = 0°C to +85°C. Typical values are at TA = +25NC, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS SEQUENCE CONTROL EN Pulldown Resistance DLY1 Charge Current 1 VDLY1 = 1V; when DLY1 cap is not used, there is no delay EN, DLY1 Turn-On Threshold MI 6 8 10 FA 1.
PAGE 7
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs (Circuit of Figure 1, VINVL= VIN2 = 12V, VVOP = VVREF_I = 15V, TA = 0°C to +85°C. Typical values are at TA = +25NC, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS 0.6 V SWITCHING FREQUENCY SELECTION FSEL Input Low Voltage 500kHz FSEL Input High Voltage 750kHz 1.6 FSEL Pullup Resistance V 1 MI ELECTRICAL CHARACTERISTICS (VINVL = VIN2 = 12V, VVOP = VVREF_I = 15V, TA = -40NC to +85NC.
PAGE 8
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs ELECTRICAL CHARACTERISTICS (continued) (VINVL = VIN2 = 12V, VVOP = VVREF_I = 15V, TA = -40NC to +85NC.) (Note 3) PARAMETER CONDITIONS MIN TYP MAX UNITS STEP-UP REGULATOR Output-Voltage Range VIN 20 V Oscillator Maximum Duty Cycle 70 85 % 1.2375 1.2625 V 0.96 1.04 V 150 560 FS 40 FA 3.6 4.
PAGE 9
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs (VINVL = VIN2 = 12V, VVOP = VVREF_I = 15V, TA = -40NC to +85NC.) (Note 3) PARAMETER CONDITIONS MIN TYP MAX UNITS OPERATIONAL AMPLIFIERS VOP Supply Range 8 20 V 20.
PAGE 10
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs ELECTRICAL CHARACTERISTICS (continued) (VINVL = VIN2 = 12V, VVOP = VVREF_I = 15V, TA = -40NC to +85NC.) (Note 3) PARAMETER CONDITIONS MIN TYP MAX UNITS GAMMA REFERENCE 18.0 V VREF_I Undervoltage Lockout VREF_I Input Voltage Range VREF_I rising 5.2 V VREF_I Input Bias Current No load 250 FA VREF_O Dropout Voltage IVREF_O = 60mA VREF_FB Regulation Voltage 10 VREF_I = 13.
PAGE 11
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs STEP-DOWN REGULATOR EFFICIENCY vs. LOAD CURRENT 70 500kHz 65 60 MAX17126 toc02 750kHz 750kHz OUTPUT VOLTAGE (V) EFFICIENCY (%) 80 75 3.350 MAX17126 toc01 85 STEP-DOWN REGULATOR OUTPUT VOLTAGE vs. LOAD CURRENT 3.325 3.300 500kHz 55 50 0.10 3.275 10.00 1.00 LOAD CURRENT (A) 0 STEP-DOWN REGULATOR LOAD TRANSIENT RESPONSE (0.3A TO 1.8A) 0.80 1.20 1.60 LOAD CURRENT (A) 2.00 2.
PAGE 12
Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) STEP-UP REGULATOR PULSED LOAD TRANSIENT RESPONSE (0.1A TO 1.9mA) STEP-UP REGULATOR LOAD TRANSIENT RESPONSE (0.1A TO 1.1A) MAX17126 toc08 MAX17126 toc07 ILOAD 1A/div 0V ILOAD 1A/div 0A VAVDD (AC-COUPLED) 200mV/div 0A VAVDD (AC-COUPLED) 200mV/div 0A IL1 1A/div 0A IL1 1A/div 0V 10Fs/div 20Fs/div L = 10FH L = 10FH SWITCHING FREQUENCY vs. INPUT VOLTAGE STEP-UP REGULATOR HEAVY LOAD SOFT-START (0.
PAGE 13
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs POSITIVE CHARGE-PUMP REGULATOR NORMALIZED LOAD REGULATION POSITIVE CHARGE-PUMP REGULATOR NORMALIZED LINE REGULATION -4 IGON = 25mA -6 -8 -10 MAX17126 toc15 IGON = 0A -2 0.5 OUTPUT CURRENT ERROR (%) 0 -0.5 -1.0 -1.5 -2.0 -12 10 11 12 13 14 15 16 SUPP VOLTAGE (V) 0 18 17 NEGATIVE CHARGE-PUMP REGULATOR NORMALIZED LINE REGULATION POSITIVE CHARGE-PUMP REGULATOR LOAD-TRANSIENT RESPONSE 0.
PAGE 14
Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) OP AMP SUPPLY CURRENT vs. SUPPLY VOLTAGE POWER-UP SEQUENCE OF ALL SUPPLY OUTPUTS MAX17126 toc19 0V VOUT 0V 0V VGOFF VAVDD VGON 0V 0V VCOM VDLY1 0V 0V 0V VGHM 0V MAX17126 toc20 2.65 VIN 2.60 VOP SUPPLY CURRENT (mA) MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs 2.55 2.50 2.45 2.40 2.35 2.
PAGE 15
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs OPERATIONAL AMPLIFIER SMALL-SIGNAL STEP RESPONSE VIN SUPPLY CURRENT vs.
PAGE 16
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Pin Description PIN NAME 1 VREF_I FUNCTION Gamma Reference Input 2 VOP Operational Amplifier Power Supply 3 OGND Operational Amplifier Power Ground 4 OPP 5 OPN Operational Amplifier Noninverting Input Operational Amplifier Inverting Input 6 OPO Operational Amplifier Output 7 PGOOD Input voltage power-good open-drain output pulled high to VL or 3.3V through 10kI resistor.
PAGE 17
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs PIN NAME FUNCTION 30 GD Step-Up Regulator External pMOS Pass Switch Gate Input. A 10FA P 20% current source pulls down on the gate of the external pFET when EN is high. 31 FB1 Boost Regulator Feedback Input. Connects FB1 to the center of a resistive voltage-divider between the boost regulator output and GND to set the boost regulator output voltage. Place the resistive voltagedivider within 5mm of FB1.
PAGE 18
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs VIN 12V C1 L1 10µH 0.1µF D1 BST LX1 IN2 C4 LX1 IN2 C2 PGND PGND FB1 COMP L2 OUT 3.3V, 1.5A D2 C5 LX2 FSEL LX2 CLIM RCOMP 25kI R2 CCOMP 1nF R1 OUT GD_I Q1 GD VL (OR 3.3V) FB2 R7 68.1kI PGOOD VIN VIN 10kI MAX17126 MAX17126A INVL AVDD 16V, 1A VDET C3 0.1µF R8 422kI VL VL VOP REF OPN GND OGND 1µF REF OPP 0.22µF ON/OFF OPO 2.2kI 1kI EN DRN 13.
PAGE 19
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Detailed Description The typical operating circuit (Figure 1) of the MAX17126/ MAX17126A comprise a complete power-supply system for TFT LCD TV panels. The circuit generates a +3.3V logic supply, a +16V source driver supply, a +35V positive gate-driver supply, a -6V negative gate-driver supply, and a P 0.5% high-accuracy, high-voltage gamma reference.
PAGE 20
VIN L1 BST IN2 OUT LX1 VL LX2 STEP-DOWN REG STEP-UP REG OSC PGND FB1 COMP OUT FSEL CLIM GD_I GD FB2 VIN VL (OR 3.
PAGE 21
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs PWM Controller Block The heart of the PWM control block is a multi-input, openloop comparator that sums three signals: the outputvoltage signal with respect to the reference voltage, the current-sense signal, and the slope-compensation signal. The PWM controller is a direct-summing type, lacking a traditional error amplifier and the phase shift associated with it.
PAGE 22
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs PWM Controller Block An error amplifier compares the signal at FB1 to 1.25V and changes the COMP output. The voltage at COMP sets the peak inductor current. As the load varies, the error amplifier sources or sinks current to the COMP output accordingly to produce the inductor peak current necessary to service the load.
PAGE 23
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs During the first half cycle, N1 turns on and charges flying capacitors C12 and C13 (Figure 3). During the second half cycle, N1 turns off and P1 turns on, level shifting C12 and C13 by VSUPP volts. If the voltage across C15 (VGH) plus a diode drop (VD) is smaller than the level-shifted flying-capacitor voltage (VC13) plus VSUPP, charge flows from C13 to C15 until the diode (D3) turns off.
PAGE 24
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs REF MAX17126 MAX17126A 10µA DLY1 Q4 FAULT SHDN EN GD DONE VGH VREF Q1 VGHM 9R 1kI R GVOFF Q2 DRN THR Figure 5. Switch Control The negative charge-pump regulator is enabled after the step-down regulator finishes soft-start. Each time it is enabled, the negative charge-pump regulator goes through a soft-start routine by ramping down its internal reference voltage from 1.
PAGE 25
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs MAX17126 MAX17126A VOP OPP ±4V 500 High-Accuracy, High-Voltage Gamma Reference The LDO is typically used to drive gamma-correction divider string. Its output voltage is adjustable through a resistor-divider. This LDO features high output accuracy (Q0.5%) and low-dropout voltage (0.25V typ) and can supply at least 60mA.
PAGE 26
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Power-Up Sequence The step-down regulator starts up when the MAX17126/ MAX17126As’ internal reference voltage (REF) is above its undervoltage lockout (UVLO) threshold. Once the step-down regulator soft-start is done, the FB2 faultdetection circuit and the negative charge pump are enabled. Negative charge-pump fault protection is enabled after its own soft-start is done.
PAGE 27
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Gamma reference GREF stays flat until AVDD does not have enough headroom. A pMOS switch turns on after VL drops below its UVLO threshold to guarantee GREF does not go over AVDD. PGOOD is pulled low after its input voltage (buck output in this case) drops below the designed threshold. After VL drops below its UVLO threshold, PGOOD gives up control and is resistively pulled up to its input voltage.
PAGE 28
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs where IOUT(MAX) is the maximum DC load current, and the switching frequency fSW is 750kHz when FSEL is tied to VL, 500kHz when FSEL is tied to GND. The exact inductor value is not critical and can be adjusted to make trade-offs among size, cost, and efficiency.
PAGE 29
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs The amplitude of the ESR step is a function of the load step and the ESR of the output capacitor: VOUT_ESR_STEP = DIOUT × R ESR_OUT The amplitude of the capacitive sag is a function of the load step, the output capacitor value, the inductor value, the input-to-output voltage differential, and the maximum duty cycle: VOUT_SAG = L 2 × (DIOUT ) 2 ( 2 × C OUT × VIN2(MIN) × D MAX - VOUT ) The amplitude of the capac
PAGE 30
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Calculate the ripple current at that operating point and the peak current required for the inductor: I AVDD_RIPPLE = ( VIN(MIN) × VAVDD - VIN(MIN) ) L AVDD × VAVDD × fSW I I AVDD_PEAK = IIN(DC,MAX) + AVDD_RIPPLE 2 The inductor’s saturation current rating and the MAX17126/ MAX17126As’ LX1 current limit should exceed IAVDD_ PEAK and the inductor’s DC current rating should exceed IIN(DC,MAX).
PAGE 31
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Charge-Pump Regulators Selecting the Number of Charge-Pump Stages For highest efficiency, always choose the lowest number of charge-pump stages that meet the output requirement.
PAGE 32
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs High-Accuracy, High-Voltage Gamma Reference Output-Voltage Selection The output voltage of the high-accuracy LDO is set by connecting a resistive voltage-divider from the output (VREF_O) to AGND with the center tap connected to VREF_FB (see Figure 1). Select R10 in the 10kI to 50kI range.
PAGE 33
Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs PACKAGE TYPE PACKAGE CODE OUTLINE No. LAND PATTERN No. 48 TQFN T4877-3 21-0144 90-0129 LX1 PGND PGND GD_I GD FB1 COMP THR CPGND SUPP DRVP LX1 SS FBP 38 23 CLIM VGH 39 22 FSEL VGHM 40 21 VL DRN 41 20 INVL SUPN 42 19 VDET DRVN 43 18 GND GND 44 17 IN2 FBN 45 16 IN2 46 15 BST REF MAX17126 MAX17126A LX2 3 4 5 6 7 8 9 10 11 12 N.C.
PAGE 34
MAX17126/MAX17126A Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Revision History REVISION NUMBER REVISION DATE 0 6/09 Initial release 1 3/10 MAX17126A added to data sheet DESCRIPTION PAGES CHANGED — 1-33 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.