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 a
throughput rate of 105 kSPS. The devices include a shutdown
mode that reduces current consumption to less than 6 μA.
To reduce the effects of noise from LCDs and other sources, the
AD7879/AD7889 contain a preprocessing block. The
preprocessing 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 ADCs, as a battery monitor,
or as a general-purpose input/output (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 devices support
an SPI interface (AD7879/AD7889) or an I2C interface (AD7879-1/
AD7889-1).
Applications
- Personal digital assistants
- Smart handheld devices
- Touch screen monitors
- Point-of-sale terminals
- Medical devices
- Cell phones
