MAX8784

MAX8784
XX-XXXX; Rev 0; 1/07
KIT
ATION
EVALU
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A
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Step-Up Regulator, Internal Charge Pumps, Switch
Control, and Operational Amplifier for TFT LCDs
The MAX8784 generates supply rails for the thin-film
(TFT) liquid-crystal display (LCD) panels in TVs and
monitors. It includes a step-up regulator, a regulated
positive- and a negative-charge pump, three high-current operational amplifiers, and Dual Mode™, logic-controlled, high-voltage switch control block. HVS mode
automatically increases the output voltages of the boost
regulator and the positive-charge pump to stress test
display panels during production. The MAX8784 can
operate from input voltages of 4V to 5.5V and is optimized for LCD TV panel and LCD monitor applications.
The step-up DC-DC regulator provides a regulated supply voltage for TFT source drivers. The step-up regulator
is a high-frequency (1.2MHz), high-efficiency, currentmode regulator. The step-up regulator has a built-in
110mΩ (typ) power MOSFET. The high-switching frequency allows the use of ultra-small inductors and
ceramic capacitors. The current-mode architecture provides fast transient response and easy compensation.
The step-up regulator features output undervoltage protection, soft-start, internal current limit, and adjustable
output voltage by an external resistive divider.
The three operational amplifiers drive the LCD backplane and the gamma-correction-divider string. Each
operational amplifier has a fast slew rate (45V/µs), a
wide bandwidth (20MHz), and a high-output short-circuit current (200mA). Each op amp has rail-to-rail input
and rail-to-rail output operation.
The positive-charge pump regulator and the negativecharge pump regulator provide regulated supply voltages for the TFT gate drivers. The positive-charge
pump is a two-stage charge pump, which requires no
external diodes. The output voltages of both charge
pumps are resistor adjustable. The logic-controlled
high-voltage switch allows the manipulation of the positive TFT gate-driver supply.
Features
o Step-Up Regulator Supply for LCD Panel Source
Driver
Fast Transient Response to Pulsed Load
Built-In 18V, 4A, 0.11Ω n-Channel Power
MOSFET with Lossless Current Sensing
Cycle-by-Cycle Current-Limit Comparator
90% Efficiency (5V In to 15V Out)
1.2MHz Switching Frequency
o Three High-Current 19V
180mA Output Short-Circuit Current
45V/µs Slew Rate
20MHz Bandwidth
Rail-to-Rail Input and Output Operation
o Regulated Charge-Pump Tripler with Integrated
Diodes for TFT Gate-On Supply
o Regulated Charge Pump for TFT Gate-Off Supply
o Built-In Sequencing
Internal Digital Soft-Start
36V Gate-On Switch
Startup Timing Capacitors for AVDD and GON
o Undervoltage and Thermal Protection
o 4V to 5.5V Input Operating Range
Simplified Operating Circuit
STEP-UP
OUTPUT
VIN
LX
VCC
POS1
TO
VCOM
STEP-UP
OUTPUT
TO
VCOM
PGND
NEG1
OUT1
FB
POS2
NEG2
COMP
OUT2
TO
VCOM
The MAX8784 is available in a small (5mm x 5mm), lowprofile (0.8mm), 40-pin thin QFN package and operates
over the -40°C to +85°C temperature range.
VIN
POS3
RSET
OUT3
GDEL
ADEL
HVS
REF
MAX8784
CTL
AGND
Applications
SHDN
FBN
LCD TVs and LCD Monitors
GON
TCON
ON/OFF
VGON
DRN
Ordering Information
PART
TEMP RANGE
PINPACKAGE
MAX8784ETL+
-40°C to +85°C
40 Thin QFN
5mm x 5mm
PKG CODE
VGOFF
POUT
DRVN
PGND
FBP
SUP C1N
C1P C2N
STEP-UP
OUTPUT
C2P
T4055-1
STEP-UP
OUTPUT
Dual Mode is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ Maxim Integrated Products
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.
1
MAX8784
General Description
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