General Description
The MAX1778/MAX1880–MAX1885 multiple-output
DC-DC converters provide the regulated voltages
required by active matrix thin-film transistor (TFT) liquid
crystal displays (LCD) in a low-profile TSSOP package.
One high-power step-up converter and two low-power
charge pumps convert the 2.7V to 5.5V input voltage
into three independent output voltages. A built-in linear
regulator and VCOM buffer complete the power-supply
requirements.
The main step-up converter accurately generates an
externally set output voltage up to 13V that can supply
the display’s row/column drivers. The converter’s high
switching frequency and current-mode PWM architec-
ture provide fast transient response and allow the use
of small low-profile inductors and ceramic capacitors.
The low-power BiCMOS control circuitry and internal
14V switch (0.35Ω N-channel MOSFET) enable efficien-
cies up to 91%.
The dual low-power charge pumps (MAX1778/
MAX1880/MAX1881/MAX1882 only) independently reg-
ulate one positive output (V
POS
) and one negative out-
put (V
NEG
). These low-power outputs use external
diode and capacitor stages (as many stages as
required) to regulate output voltages up to +40V and
-40V. A unique control scheme minimizes output ripple
as well as capacitor sizes for both charge pumps.
A resistor-programmable, 40mA, low-dropout linear
regulator (MAX1778/MAX1881/MAX1883/MAX1884
only) provides preregulation or postregulation for any of
the supplies. For higher current applications, an exter-
nal transistor can be added. Additionally, the VCOM
buffer provides a high current output that is ideal for
driving the capacitive backplane of TFT LCD panels.
The VCOM buffer’s output voltage is preset with an
internal 50% resistive-divider or can be externally
adjusted for other voltages.
The MAX1778/MAX1880–MAX1885 are protected
against output undervoltage and thermal overload con-
ditions by a latched fault detection circuit that shuts
down the device. All devices are available in the ultra-
thin TSSOP package (1.1mm max height).
Applications
TFT LCD Notebook Displays
TFT LCD Desktop Monitor Panels
Features
♦ 500kHz/1MHz Current-Mode PWM Step-Up
Regulator
Up to +13V Main High-Power Output
±1% Accurate
High Efficiency (91%)
♦ Dual Regulated Charge-Pump Outputs
(MAX1778/MAX1880/MAX1881/MAX1882 only)
Up to +40V Positive Charge-Pump Output
Up to -40V Negative Charge-Pump Output
♦ Low-Dropout 40mA Linear Regulator
(MAX1778/MAX1881/MAX1883/MAX1884 only)
Up to +15V LDO Input
♦ Optional Higher Current with External Transistor
♦ 2.7V to 5.5V Input Supply
♦ Internal Supply Sequencing and Soft-Start
♦ Power-Ready Output
♦ Adjustable Fault-Detection Latch
♦ Thermal Protection (+160°C)
♦ 0.1µA Shutdown Current
♦ 0.7mA IN Quiescent Current
♦ Ultra-Small External Components
♦ Thin TSSOP Package (1.1mm max height)
MAX1778/MAX1880–MAX1885
Quad-Output TFT LCD DC-DC
Converters with Buffer
________________________________________________________________ Maxim Integrated Products 1
19-1979; Rev 0a; 3/01
Ordering Information
