The AD7879/AD7889 are 12-bit successive approximation analog-to-digital converters (SAR ADCs) with a synchronous
serial interface and low on-resistance switches for driving 4-wire
resistive touch screens. The AD7879/AD7889 work with a very low power supply°a single 1.6 V to 3.6 V supply°and feature
throughput rates of 105 kSPS. The devices include a shutdown
mode that reduces current consumption to less than 6 °A.
To reduce the effects of noise from LCDs and other sources, the
AD7879/AD7889 contain a preprocessing block. The prepro-
cessing function consists of a median filter and an averaging filter. The combination of these two filters 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/AD7889 can run in
slave mode or standalone (master) mode, using an automatic
conversion sequencer and timer.
The AD7879/AD7889 have a programmable pin that can operate
as an auxiliary input to the ADC, as a battery monitor, or as a GPIO. In addition, a programmable interrupt output can operate in three modes: as a general-purpose interrupt to signal when new data is available (DAV), as an interrupt to indicate when limits are exceeded (INT), or as a pen-down interrupt when the screen is touched (PENIRQ). The AD7879/AD7889 offer temperature measurement 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 AD7889 is available in a backside-coated version of the WLCSP. Both parts support an SPI interface (AD7879/AD7889) or an I2C® interface (AD7879-1/AD7889-1).
