The AD7877 is a 12-bit， successive approximation ADC with a synchronous serial interface and low on resistance switches for driving touch screens. The AD7877 operates from a single 2.7 V to 5.25 V power supply （functional operation to 2.2 V）， and features throughput rates of 125 kSPS. The AD7877 features direct battery measurement on two inputs， temperature and touch-pressure measurement. The AD7877 also has an on-board reference of 2.5 V. When not in use， it can be shut down to conserve power. An external reference can also be applied and varied from 1 V to +VCC， with an analog input range of 0 V to VREF. The device includes a shutdown mode that reduces its current consumption to less than 1 μA. To reduce the effects of noise from LCDs， the acquisition phase of the on-board ADC is controlled via the STOPACQ pin. Userprogrammable conversion controls include variable acquisition time and first conversion delay. Up to 16 averages can be taken per conversion. There is also an on-board DAC for LCD backlight or contrast control. The AD7877 runs in either slave or master mode using a conversion sequencer and timer. It is ideal for battery-powered systems such as personal digital assistants with resistive touch screens and other portable equipment. The part is available in a 32-lead lead frame chip scale package （LFCSP）， and a 25-ball wafer level chip scale package （WLCSP）