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Multi-Output Power Supplies with VCOM Amplifier

and High-Voltage Gamma Reference for LCD TVs

MAX17126B

EVALUATION KIT AVAILABLE

General Description

The MAX17126B generates 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 device 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

protects the step-up and step-down power supplies

against fault conditions. The device provides soft-start

functions to limit inrush current during startup. In addi-

tion, the device integrates a control 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 device includes one high-current operational ampli-

fier designed to drive the LCD backplane (VCOM). The

amplifier features high output current (Q200mA), fast

slew rate (45V/Fs), wide bandwidth (20MHz), and rail-to-

rail outputs.

Also featured in the device is a high-accuracy, high-

voltage adjustable reference for gamma correction.

The device is available in a small (7mm x 7mm), ultra-thin

(0.8mm), 48-pin TQFN package and operates over the

-40NC to +85NC temperature range.

Applications

LCD TV Panels

Features

S 8.0V to 16.5V IN Supply Voltage Range

Selectable Frequency (500kHz/750kHz)

Current-Mode Step-Up Regulator

Fast Load-Transient Response

High-Accuracy Output Voltage (1.0%)

Built-In 20V, 3.5A, 100mI MOSFET

High Efficiency

Adjustable Soft-Start

Adjustable Current Limit

Low Duty-Cycle Operation (13.2V

- 13.5V AVDD)

Current-Mode Step-Down Regulator

Fast Load-Transient Response

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

High Efficiency

3ms Internal Soft-Start

Adjustable Positive Charge-Pump Regulator

Adjustable Negative Charge-Pump Regulator

Integrated High-Voltage Switch with Adjustable

Turn-On Delay

S High-Speed Operational Amplifier

±200mA Short-Circuit Current

45V/µs Slew Rate

High-Accuracy Reference for Gamma Buffer

±1% Feedback Voltage

Up to 30mA Load Current

Low-Dropout Voltage 0.5V at 60mA

External p-Channel Gate Control for AVDD

Sequencing

S XAO Comparator

Input Undervoltage Lockout and Thermal-

Overload Protection

S 48-Pin, 7mm x 7mm, TQFN Package

19-6050; Rev 0; 9/11

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

*EP = Exposed pad.

Ordering Information

Visit www.maximintegrated.com/products/patents for

product patent marking information.

PART TEMP RANGE PIN-PACKAGE

MAX17126BETM+

-40NC to +85NC

48 TQFN-EP*

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

Summary of content (34 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs General Description The MAX17126B generates all the supply rails for thinfilm 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 highaccuracy high-voltage gamma reference, and a highvoltage switch control block.
PAGE 2
MAX17126B 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, XAO, VDET, VREF_FB, OUT to GND..............-0.3V, (VL+ 0.3) GD, GD_I to GND...................................................-0.
PAGE 3
MAX17126B 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 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.
PAGE 4
MAX17126B 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 CONDITIONS MIN TYP MAX VFB1 = 1.1V, RCLIM = unconnected 3.0 3.5 4.2 VFB1 = 1.1V, with RCLIM at CLIM pin -20% 3.5 (68k/ RCLIM) +20% RCLIM = 60.5kI 0.56 0.625 0.69 V 0.
PAGE 5
MAX17126B 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 VOP Overvoltage Fault Threshold VOP Supply Current CONDITIONS MIN TYP MAX UNITS VVOP = rising, hysteresis = 200mV (Note 2) 20.
PAGE 6
MAX17126B 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 1.19 1.25 1.
PAGE 7
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs ELECTRICAL CHARACTERISTICS (VINVL = VIN2 = 12V, VVOP = VVREF_I = 15V, TA = -40NC to +85NC.) (Note 3) PARAMETER CONDITIONS MIN TYP MAX UNITS V GENERAL INVL, IN2 Input-Voltage Range 8 16.5 FSEL = INVL or high impedance 630 870 FSEL = GND 420 580 INVL rising, 150mV typical hysteresis 6.0 8.0 V VL Output Voltage IVL = 25mA, VFB1 = VFB2 = VFB = 1.1V, VFBN = 0.
PAGE 8
MAX17126B 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 FB1 Regulation Voltage FB1 = COMP, CCOMP = 1nF FB1 Fault Trip Level Falling edge 0.96 1.04 V FB1 Transconductance DI = Q2.
PAGE 9
MAX17126B 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.
PAGE 10
MAX17126B 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
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) STEP-DOWN REGULATOR EFFICIENCY vs. LOAD CURRENT 70 500kHz 65 60 MAX17126B toc02 750kHz 750kHz OUTPUT VOLTAGE (V) EFFICIENCY (%) 80 75 3.350 MAX17126B toc01 85 STEP-DOWN REGULATOR OUTPUT VOLTAGE vs. LOAD CURRENT 3.325 3.300 500kHz 55 50 0.10 3.275 10.00 1.
PAGE 12
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs 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.
PAGE 13
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) POSITIVE CHARGE-PUMP REGULATOR NORMALIZED LOAD REGULATION POSITIVE CHARGE-PUMP REGULATOR NORMALIZED LINE REGULATION -4 IGON = 25mA -6 -8 -10 MAX17126B toc15 IGON = 0A -2 0.5 OUTPUT CURRENT ERROR (%) 0 -0.5 -1.0 -1.5 -2.
PAGE 14
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) OP AMP SUPPLY CURRENT vs. SUPPLY VOLTAGE POWER-UP SEQUENCE OF ALL SUPPLY OUTPUTS MAX17126B toc20 VOUT 0V 0V VGOFF VAVDD VGON 0V 0V VCOM VDLY1 0V 0V 0V VGHM 0V 2.60 VOP SUPPLY CURRENT (mA) 0V MAX17126B toc21 2.65 VIN 2.55 2.50 2.45 2.40 2.35 2.
PAGE 15
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) HIGH-VOLTAGE SWITCH CONTROL FUNCTION (VGHM WITH 470pF LOAD) VIN SUPPLY CURRENT vs.
PAGE 16
MAX17126B 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 XAO Voltage Detector Output 8 GVOFF 9 EN Enable Input.
PAGE 17
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Pin Description (continued) 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.
PAGE 18
MAX17126B 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 XAO VIN VIN 10kI MAX17126B 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 13.3kI DLY1 0.
PAGE 19
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Typical Operating Circuit Detailed Description The typical operating circuit (Figure 1) of the device comprises 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
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs 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
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Step-Down Regulator The step-down regulator consists of an internal n-channel MOSFET with gate driver, a lossless current-sense network, a current-limit comparator, and a PWM controller block. The external power stage consists of a Schottky diode rectifier, an inductor, and output capacitors. The output voltage is regulated by changing the duty cycle of the high-side MOSFET.
PAGE 22
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs On the rising edge of the internal 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. Once the sum of the currentfeedback signal and the slope compensation exceed the COMP voltage, the controller resets the flip-flop and turns off the MOSFET.
PAGE 23
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs 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. The amount of charge transferred to the output is determined by the error amplifier that controls N1’s on-resistance.
PAGE 24
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs REF MAX17126B 10µA DLY1 Q4 FAULT SHDN EN GD DONE VGH VREF Q1 VGHM 9R 1kI R GVOFF Q2 DRN THR Figure 5. Switch Control High-Voltage Switch Control The device’s high-voltage switch control block (Figure 5) consists of two high-voltage p-channel MOSFETs: Q1, between VGH, and VGHM and Q2, between VGHM and DRN. The switch control block is enabled when VDLY1 exceeds VREF.
PAGE 25
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Short-Circuit Current Limit and Input Clamp The operational amplifier limits short-circuit current to approximately Q200mA if the output is directly shorted to VOP or to OGND. If the short-circuit condition persists, the junction temperature of the IC rises until it reaches the thermal-shutdown threshold (+160NC typ).
PAGE 26
MAX17126B 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 device’s internal reference voltage (REF) is above its undervoltage lockout (UVLO) threshold. Once the step-down regulator soft-start is done, the FB2 fault-detection circuit and the negative charge pump are enabled. Negative charge-pump fault protection is enabled after its own soft-start is done.
PAGE 27
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Power-Down Sequence The step-down regulator, step-up regulator, positive charge pump, negative charge pump, and high-voltage switching block all start to shut down when INVL drops below its UVLO threshold. VL stays flat until INVL does not have enough headroom. Reference REF starts to fall after VL drops below its UVLO threshold. Gamma reference GREF stays flat until AVDD does not have enough headroom.
PAGE 28
MAX17126B 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. Lower inductor values minimize size and cost, but they also increase the output ripple and reduce the efficiency due to higher peak currents.
PAGE 29
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs The step-down regulator’s output capacitor and ESR also affect the voltage undershoot and overshoot when the load steps up and down abruptly. The undershoot and overshoot also have two components: the voltage steps caused by ESR, and voltage sag and soar due to the finite capacitance and inductor slew rate.
PAGE 30
MAX17126B 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 device’s LX1 current limit should exceed IAVDD_PEAK and the inductor’s DC current rating should exceed IIN(DC,MAX).
PAGE 31
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs To further optimize transient response, vary RCOMP in 20% steps and CCOMP in 50% steps while observing transient response waveforms. 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
MAX17126B 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
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs U Minimize the length and maximize the width of the traces between the output capacitors and the load for best transient responses. U Minimize the size of the LX1 and LX2 nodes while keeping them wide and short. Keep the LX1 and LX2 nodes away from feedback nodes (FB1, FB2, FBP, FBN, and VREF_FB) and analog ground. Use DC traces as shield if necessary.
PAGE 34
MAX17126B Multi-Output Power Supplies with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs Revision History REVISION NUMBER REVISION DATE 0 9/11 DESCRIPTION Initial release PAGES CHANGED — 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.