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GENERAL DESCRIPTION
The AD7879W is a 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 AD7879W works 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
AD7879W contains 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 AD7879W can run in slave
Rev. 0
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FUNCTIONAL BLOCK DIAGRAM
REF+
X�CY�CX+Y+
FILTERING
RESULT
REGISTERS
CONTROL
REGISTERS
SEQUENCER
AND TIMER
REF
TEMPERATURE
SENSOR
TO
RESULT
REGISTERS
6-TO-1 MUX
AD7879W/
AD7879-1W
VCC/REF
X+
X
Y+
Y
GND
AUX/VBAT/GPIO
PENIRQ/INT/DAV
SERIAL PORT
DIN/
ADD1
DOUT/
SDA
SCL CS/
ADD0
12-BIT
SARADC
REF
Figure 1.
mode or standalone (master) mode, using an automatic
conversion sequencer and timer.
The AD7879W has 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 AD7879W offers temperature
measurement and touch-pressure measurement.
The AD7879W is available in a 16-lead, 4.4 mm �� 5.0 mm
TSSOP and 16-lead 4 mm �� 4 mm LFCSP. Both packages
support an SPI interface (AD7879W) or an I2C® interface