Data Sheet
FEATURES
4-wire touch screen interface
On-chip temperature sensor: −40°C to +85°C
On-chip 2.5 V reference
Direct battery measurement (0 V to 6 V)
Touch pressure measurement
Specified throughput rate of 125 kSPS
Single supply, V
CC
of 2.2 V to 5.25 V
Ratiometric conversion
High speed serial interface
Programmable 8-bit or 12-bit resolution
One auxiliary analog input
Shutdown mode: 1 µA maximum
16-lead QSOP, TSSOP, and LFCSP packages
Touch Screen Digitizer
FUNCTIONAL BLOCK DIAGRAM
+V
CC
PENIRQ
X+
X–
Y+
Y–
TEMP
SENSOR
PEN
INTERRUPT
AD7873
T/H
6-TO-1
I/P
MUX
AUX
BATTERY
MONITOR
V
BAT
V
REF
GND
CHARGE
REDISTRIBUTION
DAC
COMP
APPLICATIONS
Personal digital assistants
Smart hand-held devices
Touch screen monitors
Point-of-sale terminals
Pagers
2.5V
REF
BUF
+V
CC
GENERAL DESCRIPTION
The AD7873 is a 12-bit successive approximation ADC with a
synchronous serial interface and low on resistance switches for
driving touch screens. The AD7873 operates from a single 2.2 V
to 5.25 V supply, with a throughput rate of 125 kSPS.
The AD7873 features direct battery measurement, temperature
measurement, and touch pressure measurement. The AD7873
also has an on-board reference of 2.5 V that can be used for the
auxiliary input, battery monitor, and temperature measurement
modes. When not in use, the internal reference can be shut
down to conserve power. An external reference can also be
applied and varied from 1 V to V
CC
with an analog input range
from 0 V to V
REF
. The device includes a shutdown mode that
reduces the current consumption to less than 1 µA.
The AD7873 features on-board switches. This, coupled with low
power and high speed operation, makes the device ideal for
battery-powered systems with resistive touch screens. The part
is available in a 16-lead, 0.15 inch quarter size outline package
(QSOP), a 16-lead, thin shrink small outline package (TSSOP),
and a 16-lead, lead frame chip scale package (LFCSP).
DIN
SAR + ADC
CONTROL LOGIC
SPORT
02164-001
CS
DOUT
DCLK
BUSY
Figure 1.
PRODUCT HIGHLIGHTS
1.
2.
3.
4.
5.
Ratiometric conversion mode available, eliminating errors
due to on-board switch resistances.
On-board temperature sensor: −40°C to +85°C.
Battery monitor input.
Touch pressure measurement capability.
Low power consumption of 1.37 mW maximum with the
reference off, or 2.41 mW typical with the reference on, at
125 kSPS and V
CC
at 3.6 V.
Package options include 4 mm × 4 mm LFCSP.
Analog input range from 0 V to V
REF
.
Versatile serial I/O ports.
6.
7.
8.
Rev. F
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