The MAX1997/MAX1998 provide the voltages required for
active-matrix, thin-film transistor liquid-crystal displays
(TFT LCDs). Both combine a high-performance step-up
regulator with two linear-regulator controllers, input protection
switch control, and flexible sequence programming.
The MAX1997 contains two additional linearregulator
controllers and a VCOM buffer. The MAX1997/
MAX1998 can operate from input supplies of 2.7V to 5.5V
and feature multiple levels of protection circuitry, making
them complete power-supply systems for displays.
The main DC-DC converter provides the regulated supply
voltage for the display’s source-driver ICs. The converter
is a high-frequency (up to 1.5MHz) step-up regulator with
an integrated 14V N-channel MOSFET that allows the use
of ultra-small inductors and ceramic capacitors while
achieving efficiencies over 85%. Its current-mode control
architecture provides fast transient response to pulsed
loads. Internal soft-start and cycle-by-cycle current limit
help prevent input surge currents.
The positive and negative linear-regulator controllers
postregulate charge-pump outputs for TFT gate-on and
gate-off supplies. Both linear-regulator controllers, as well
as the step-up regulator, have supply-sequencing control
inputs. The three outputs can be sequenced in any order
by selecting the appropriate external components.
The MAX1997 features a high-current backplane driver
(VCOM). This buffer provides peak currents exceeding
300mA (typ) and requires only a 0.47μF output filter
capacitor. The MAX1997’s two additional linear-regulator
controllers can be used to build the gamma reference
voltage and a logic supply.
The MAX1997/MAX1998 have a unique input switch control
that can replace the typical input supply fuse. When a
fault is detected, the regulator is disconnected from the
input supply. The fault detector monitors all the regulated
output voltages and the current from the input supply. In
addition, the MAX1997/MAX1998 enter shutdown when
the internal over-temperature threshold is reached.
The MAX1997 is available in a 32-pin thin QFN package
and the MAX1998 is available in a 20-pin thin QFN package.
Both packages have a maximum thickness of
0.8mm suitable for ultra-thin LCD panels.
Applications
Notebook Computer Displays
LCD Monitors
Car Navigation Displays