REV.0
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a
AD7843
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2000
Touch Screen Digitizer
FUNCTIONAL BLOCK DIAGRAM
PEN
INTERRUPT
DCLK
GND
+V
CC
BUSY
PENIRQ
SAR + ADC
CONTROL LOGIC
SPORT
CS DOUTDIN
4-TO-1
I/P
MUX
AD7843
+V
CC
IN3
V
REF
IN4
Y–
Y+
X–
X+
T/H
CHARGE
REDISTRIBUTION
DAC
COMP
GENERAL DESCRIPTION
The AD7843 is a 12-bit successive-approximation ADC with a
synchronous serial interface and low on resistance switches for
driving touch screens. The part operates from a single 2.2 V to
5.25 V power supply and features throughput rates greater than
125 kSPS.
The external reference applied to the AD7843 can be varied
from 1 V to +V
CC
, while the analog input range is from 0 V to
V
REF
. The device includes a shutdown mode that reduces the
current consumption to less than 1 µA.
The AD7843 features on-board switches. This coupled with low
power and high-speed operation make this device ideal for
battery-powered systems such as personal digital assistants with
resistive touch screens and other portable equipment. The part
is available in a 16-lead 0.15" Quarter Size Outline (QSOP) pack-
age and a 16-lead Thin Shrink Small Outline (TSSOP) package.
FEATURES
4-Wire Touch Screen Interface
Specified Throughput Rate of 125 kSPS
Low Power Consumption:
1.37 mW Max at 125 kSPS with V
CC
= 3.6 V
Single Supply, V
CC
of 2.2V to 5.25 V
Ratiometric Conversion
High-Speed Serial Interface
Programmable 8- or 12-Bit Resolution
Two Auxiliary Analog Inputs
Shutdown Mode: 1 H9262A max
16-Lead QSOP and TSSOP Packages
APPLICATIONS
Personal Digital Assistants
Smart Hand-Held Devices
Touch Screen Monitors
Point-of-Sales Terminals
Pagers
PRODUCT HIGHLIGHTS
1. Ratiometric conversion mode available eliminating errors
due to on-board switch resistances.
2. Maximum current consumption of 380 µA while operating at
125 kSPS.
3. Power-down options available.
4. Analog input range from 0 V to V
REF
.
5. Versatile serial I/O port.