Analog Devices MAX1997 Product Info

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 al