Quad-Output TFT LCD DC-DC Converters with Buffer

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 architecture 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 (0.35≈ N-channel MOSFET) enable efficiencies up to 91%.

The dual low-power charge pumps (MAX1778/ MAX1880/MAX1881/MAX1882 only) independently regulate one positive output (VPOS) and one negative output (VNEG). 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 external 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 conditions 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 Desktop Monitor Panels * TFT LCD Notebook Displays

* 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–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)