AD7879

The AD7879 is a 12-bit successive approximation analog-to- digital converter (ADC) with a synchronous serial interface and low on-resistance switches for driving 4-wire resistive touch screens. The AD7879 works with a very low power supply (a single 1.6 V to 3.6 V) and features throughput rates of 105 kSPS.

The device includes a shutdown mode that reduces its current consumption to less than 6 A.

To reduce the effects of noise from LCDs and other sources, the AD7879 contains a preprocessing block. The preprocessing function consists of a median and an averaging filter. The com- bination of these two techniques provides a more robust solution, discarding the spurious noise in the signal and keeping only the data of interest. The size of both filters is programmable. Other user-programmable conversion controls include variable acquisition time and first conversion delay; up to 16 averages can be taken per conversion. The AD7879 can run in either slave or standalone mode, using an automatic conversion sequencer and timer.

The AD7879 has a programmable pin that can operate as an auxiliary input to the ADC, as a battery monitor, or as a GPIO. There is also a programmable interrupt output that can operate in three modes: as a general-purpose interrupt to signal when new data is available INT, as an interrupt to indicate when limits are exceeded, or as a pen-down interrupt when the screen is touched (PENIRQ).

The AD7879 offers temperature measure- ment and touch-pressure measurement. The AD7879 is available in a 12-ball, 1.6 mm * 2 mm WLCSP and in a 16-lead, 4 mm * 4 mm LFCSP. The part also has either an SPI (AD7879) or I2C (AD7879-1) interface.