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LCD power supply with fault protection

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MAXIM Integrated Products, represented by Arrow Electronics , has introduced the MAX1997/MAX1998 power supplies that provide the voltages required for active-matrix, thin-film transistor, liquid crystal displays (TFT LCD).

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 linear-regulator controllers and a VCOM buffer. The MAX1997/MAX1998 operate from 2.7V to 5.5V input supplies and feature multiple levels of protection circuitry, making a complete power supply system 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 greater than 85 per cent.

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 post-regulate 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 400mA and requires only a 0.47 microfarads 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 fuse by disconnecting the load from the input supply when a fault is detected.

The fault detector monitors all the regulated output voltages as well as the current from the input supply. In addition, the MAX1997/MAX1998 enter shutdown when the internal overtemperature threshold is reached.

The MAX1997 is available in a 32-pin QFN package and the MAX1998 is available in a 20-pin QFN package. Both packages have a maximum 1.0mm thickness suitable for ultra-thin LCD panels.

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