MAX8784 Datasheet, PDF (1/24 Pages) Maxim Integrated Products – Step-Up Regulator, Internal Charge Pumps, Switch Control, and Operational Amplifier for TFT LCDs

19-0737; Rev 0; 1/07
EVAALVUAAILTAIOBNLEKIT
Step-Up Regulator, Internal Charge Pumps, Switch
Control, and Operational Amplifier for TFT LCDs
General Description
The MAX8784 generates supply rails for the thin-film
transistor (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-con-
trolled, 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 opti-
mized for LCD TV panel and LCD monitor applications.
The step-up DC-DC regulator provides a regulated sup-
ply voltage for TFT source drivers. The step-up regulator
is a high-frequency (1.2MHz), high-efficiency, current-
mode regulator. The step-up regulator has a built-in
110mΩ (typ) power MOSFET. The high-switching fre-
quency allows the use of ultra-small inductors and
ceramic capacitors. The current-mode architecture pro-
vides fast transient response and easy compensation.
The step-up regulator features output undervoltage pro-
tection, soft-start, internal current limit, and adjustable
output voltage by an external resistive divider.
The three operational amplifiers drive the LCD back-
plane 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-cir-
cuit current (200mA). Each op amp has rail-to-rail input
and rail-to-rail output operation.
The positive charge-pump regulator and the negative
charge-pump regulator provide regulated supply volt-
ages 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 posi-
tive TFT gate-driver supply.
The MAX8784 is available in a small (5mm x 5mm), low-
profile (0.8mm), 40-pin TQFN package and operates
over the -40°C to +85°C temperature range.
Applications
LCD TVs and LCD Monitors
Ordering Information
PART
TEMP RANGE ^PIN-
PKG CODE
PACKAGE
MAX8784ETL+
-40°C to +85°C
40 TQFN
5mm x 5mm
T4055-1
+Denotes a lead(Pb)-free/RoHS-compliant package.
Dual Mode is a trademark of Maxim Integrated Products, Inc.
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 Operational Amplifiers
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
VIN
OUTPUT
STEP-UP
OUTPUT
TO
VCOM
TO
VCOM
TO
VCOM
VIN
VCC
POS1
NEG1
OUT1
POS2
NEG2
OUT2
POS3
OUT3
HVS
REF
AGND
MAX8784
FBN
VGOFF
DRVN
LX
PGND
FB
COMP
RSET
GDEL
ADEL
CTL
SHDN
GON
DRN
POUT
TCON
ON/OFF
PGND
SUP C1N
C1P C2N
FBP
C2P
STEP-UP
OUTPUT
VGON
STEP-UP
OUTPUT
________________________________________________________________ Maxim Integrated Products 1
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