The MAX8798 includes a high-performance, step-up
regulator; a high-speed operational amplifier; a digitally
adjustable VCOM calibration device with nonvolatile
memory; 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 inductors
and ceramic capacitors. The current-mode control
architecture provides fast transient response to pulsed
loads typical of source driver loads. The step-up regulator
features soft-start and current limit.
The high-current operational amplifier is designed to
drive the LCD backplane (VCOM). The amplifier features
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
lead 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 65V (maximum) between +45V (maximum) and
-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 package
with a maximum thickness of 0.8mm for ultra-thin
LCD panels.