MAX1998 Quintuple/Triple-Output TFT LCD Power Supplies with Fault Protection and VCOM Buffer

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 linear-regulator 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-to-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. The three outputs can be sequenced in any order by selecting the appropriate external components. Both linear-regulator controllers, as well as the step-up regulator, have supply-sequencing control inputs.

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 overtemperature 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.