MAX8798 Datasheet, PDF (1/30 Pages) Maxim Integrated Products – Internal-Switch Boost Regulator with Integrated 3-Channel Scan Driver for TFT LCDs

19-0971; Rev 0; 9/07
EVAALVUAAILTAIOBNLEKIT _{Internal-Switch Boost Regulator with}
Integrated 3-Channel Scan Driver for TFT LCDs
General Description
The MAX8798 includes a high-performance, step-up
regulator; a high-speed operational amplifier; a digitally
adjustable VCOM calibration device with nonvolatile
memory and an I²C interface; and a high-voltage, level-
shifting scan driver. The device is optimized for thin-film
transistor (TFT) liquid-crystal display (LCD) applications.
The step-up DC-DC converter provides the regulated
supply voltage for panel source driver ICs. The high
switching frequency allows the use of ultra-small induc-
tors and ceramic capacitors. The current-mode control
architecture provides fast transient response to pulsed
loads typical of source driver loads. The step-up regu-
lator features soft-start and current limit.
The high-current operational amplifier is designed to
drive the LCD backplane (VCOM). The amplifier fea-
tures high output current (±150mA), fast slew rate
(45V/µs), wide bandwidth (20MHz), and rail-to-rail
inputs and outputs.
The programmable VCOM calibrator is externally
attached to the VCOM amplifier’s resistive voltage-divider
and sinks a programmable current to adjust the VCOM
output-voltage level. An internal 7-bit digital-to-analog
converter (DAC) controls the sink current. The DAC is
ratiometric relative to BOOST and is guaranteed to be
monotonic over all operating conditions. The calibrator IC
includes an EEPROM to store the desired VCOM voltage
level. The 2-wire I²C interface between the LCD panel
and the programming circuit minimizes panel connector
pin count and simplifies production equipment.
The high-voltage, level-shifting scan driver is designed
to drive the TFT panel gate drivers. Its three outputs
swing from +35V (maximum) to -25V (minimum) and
can swiftly drive capacitive loads. To save power, the
two complementary outputs are designed to allow
charge sharing during state changes.
The MAX8798 is available in a 36-pin, thin QFN pack-
age with a maximum thickness of 0.8mm for ultra-thin
LCD panels.
Applications
Notebook Computer Displays
LCD Monitor Panels
Ordering Information
PART
TEMP RANGE
PIN-
PACKAGE
MAX8798ETX+ -40°C to +85°C ^{36 Thin QFN}
6mm x 6 mm
PKG
CODE
T-3666M-1
Features
o 1.8V to 5.5V IN Supply Voltage Range
o 1.8V to 4.0V V_DD Input Voltage Range
o 1.2MHz Current-Mode Step-Up Regulator
Fast Transient Response
Built-In 20V, 1.9A, 150mΩ MOSFET
o High-Speed (20MHz) Operational Amplifier
±150mA Output Current
o High-Voltage Drivers with Scan Logic
+35V to -25V Outputs
Output Charge Sharing
o Programmable VCOM Calibrator
7-Bit Adjustable Current-Sink Output
I²C Interface
EEPROM Setting Memory
o Thermal-Overload Protection
Simplified Operating Circuit
VP
VN
VIN
SYSTEM
VN
PANEL
VIN
I²C
BUS
50kΩ
SHDN
IN
LX
DISH
CPV
OE
STV
OECON
GOFF
STVP
CKVCS
CKVB
CKVBCS
1kΩ
SCAN DRIVER
LOGIC
AND
GATE DRIVERS
1.9A
STEP-UP
REG
PGND
FB
COMP
AGND
GON
BOOST
NEG
VCOM
CKV
VL
3.3V
VDD
LINEAR
REG
VCOM CALIBRATOR
GND
7
SDA
SCL
SCLS
WPP WPN
POS
BGND
OUT
SET
VMAIN
VP
TO VCOM
BACKPLANE
________________________________________________________________ Maxim Integrated Products 1
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