Touch Screen Digitizer
AD7873
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, VCC 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
APPLICATIONS
FUNCTIONAL BLOCK DIAGRAM
+VCC
PENIRQ
PEN
INTERRUPT
TEMP
SENSOR
X+
X–
AD7873
Y+
T/H
Y–
6-TO-1
I/P
MUX
AUX
COMP
BATTERY
MONITOR
VBAT
VREF
Personal digital assistants
Smart hand-held devices
Touch screen monitors
Point-of-sale terminals
Pagers
GND
2.5V
REF
CHARGE
REDISTRIBUTION
DAC
BUF
+VCC
SAR + ADC
CONTROL LOGIC
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 power supply and features throughput rates greater
than 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 can be varied from 1 V to VCC and the analog input
range is from 0 V to VREF. 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 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 package
(QSOP), a 16-lead, thin shrink small outline package (TSSOP),
and a 16-lead, lead frame chip scale package (LFCSP).
DIN
CS
DOUT
DCLK
BUSY
02164-001
SPORT
Figure 1.
PRODUCT HIGHLIGHTS
1.
Ratiometric conversion mode available, eliminating errors
due to on-board switch resistances.
2.
On-board temperature sensor: −40°C to +85°C.
3.
Battery monitor input.
4.
Touch pressure measurement capability.
5.
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 VCC at 3.6 V.
6.
Package options include 4 mm × 4 mm LFCSP.
7.
Analog input range from 0 V to VREF.
8.
Versatile serial I/O ports.
Rev. E
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rights of third parties that may result from its use. Specifications subject to change without notice. No
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