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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
AD7873
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
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2013 Analog Devices, Inc. All rights reserved.
AD7873
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Product Highlights ........................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Timing Specifications .................................................................. 5
Absolute Maximum Ratings............................................................ 6
Thermal Resistance ...................................................................... 6
ESD Caution .................................................................................. 6
Pin Configurations and Function Descriptions ........................... 7
Terminology ...................................................................................... 8
Typical Performance Characteristics ............................................. 9
Data Sheet
Circuit Information ........................................................................ 13
ADC Transfer Function ............................................................. 13
Typical Connection Diagram ................................................... 13
Analog Input ............................................................................... 14
Measurements ............................................................................. 16
Pen Interrupt Request ................................................................ 18
Control Register ......................................................................... 19
Power vs. Throughput Rate ....................................................... 20
Serial Interface ............................................................................ 21
Grounding and Layout .................................................................. 23
PCB Design Guidelines for Chip Scale Package .................... 23
Outline Dimensions ....................................................................... 24
Ordering Guide .......................................................................... 25
REVISION HISTORY
2/13—Rev. E to Rev. F
Changes to General Description Section ...................................... 1
Added EPAD Note to Figure 3 and Table 5................................... 7
Updated Outline Dimensions ....................................................... 24
Changes to Ordering Guide .......................................................... 26
9/06—Rev. D to Rev. E
Changes to Figure 13 Caption ...................................................... 10
Updated Outline Dimensions ....................................................... 24
Changes to Ordering Guide .......................................................... 25
6/04—Rev. C to Rev. D
Updated Format .................................................................. Universal
Changes to Absolute Maximum Ratings ....................................... 6
Additions to PD0 and PD1 Description ...................................... 21
PBC Guidelines for Chip Scale Package Added ......................... 23
Additions to Ordering Guide ........................................................ 25
4/03—Rev. B to Rev. C
Changes to Formatting ...................................................... Universal
Updated Outline Dimensions ....................................................... 19
1/02—Rev. A to Rev. B
Addition of 16-Lead Lead Frame Chip Scale Package .. Universal
Edits to Features.................................................................................1
Edits to General Description ...........................................................1
Addition of LFCSP Pin Configuration ...........................................4
Edit to Absolute Maximum Ratings................................................4
Addition to Ordering Guide ............................................................4
Addition of CP-16 Outline Dimensions .................................... 19
2/01—Rev. 0 to Rev A
Edits to Notes in the Ordering Guide
Rev. F | Page 2 of 28
Data Sheet
SPECIFICATIONS
V
CC
= 2.7 V to 3.6 V, V
REF
= 2.5 V internal or external, f
DCLK
= 2 MHz; T
A
= −40°C to +85°C, unless otherwise noted.
Table 1.
Parameter
DC ACCURACY
Resolution
No Missing Codes
Integral Nonlinearity
2
Differential Nonlinearity
2
Offset Error
2
Gain Error
2
Noise
Power Supply Rejection
SWITCH DRIVERS
On Resistance
2
Y+, X+
Y–, X–
ANALOG INPUT
Input Voltage Ranges
DC Leakage Current
Input Capacitance
REFERENCE INPUT/OUTPUT
Internal Reference Voltage
Internal Reference Tempco
V
REF
Input Voltage Range
DC Leakage Current
V
REF
Input Impedance
TEMPERATURE MEASUREMENT
Temperature Range
Resolution
Differential Method
3
Single Conversion Method
4
Accuracy
Differential Method
3
Single Conversion Method
4
BATTERY MONITOR
Input Voltage Range
Input Impedance
Accuracy
LOGIC INPUTS
Input High Voltage, V
INH
Input Low Voltage, V
INL
Input Current, I
IN
Input Capacitance, C
IN 5
AD7873A
1
12
11
±2
±6
±4
70
70
AD7873B
1
12
12
±1
–0.9/+1.5
±6
±4
70
70
Unit
Bits
Bits min
LSB max
LSB max
LSB max
LSB max
µV rms typ
dB typ
Test Conditions/Comments
AD7873
+V
CC
= 2.7 V
External reference
5
6
0 to V
REF
±0.1
37
2.45/2.55
±15
1/V
CC
±1
1
5
6
0 to V
REF
±0.1
37
2.45/2.55
±15
1/V
CC
±1
1
Ω typ
Ω typ
V
µA typ
pF typ
V min/max
ppm/°C typ
V min/max
µA max
GΩ typ
CS = GND or +V
CC
; typically 260 Ω when the
on-board reference is enabled
–40/+85
1.6
0.3
±2
±2
0/6
10
±2.5
±3
2.4
0.4
±1
10
–40/+85
1.6
0.3
±2
±2
0/6
10
±2
±3
2.4
0.4
±1
10
°C min/max
°C typ
°C typ
°C typ
°C typ
V min/max
kΩ typ
% max
% max
V min
V max
µA max
pF max
Sampling; 1 GΩ when battery monitor is off
External reference
Internal reference
Typically 10 nA, V
IN
= 0 V or +V
CC
Rev. F | Page 3 of 28
AD7873
Parameter
LOGIC OUTPUTS
Output High Voltage, V
OH
Output Low Voltage, V
OL
PENIRQ Output Low Voltage, V
OL
Floating-State Leakage Current
Floating-State Output Capacitance
5
Output Coding
CONVERSION RATE
Conversion Time
Track-and-Hold Acquisition Time
Throughput Rate
POWER REQUIREMENTS
+V
CC
(Specified Performance)
I
CC 6
Normal Mode (f
SAMPLE
= 125 kSPS)
Normal Mode (f
SAMPLE
= 12.5 kSPS)
Normal Mode (Static)
Shutdown Mode (Static)
Power Dissipation
6
Normal Mode (f
SAMPLE
= 125 kSPS)
Shutdown
1
2
Data Sheet
AD7873A
1
V
CC
– 0.2
0.4
0.4
±10
10
AD7873B
1
Unit
Test Conditions/Comments
I
SOURCE
= 250 µA; V
CC
= 2.2 V to 5.25 V
I
SINK
= 250 µA
100 kΩ pull-up; I
SINK
= 250 µA
V
CC
– 0.2
V min
0.4
V max
0.4
V max
±10
µA max
10
pF max
Straight (Natural) Binary
12
3
125
2.7/3.6
380
670
170
150
580
1
1.368
2.412
3.6
DCLK cycles max
DCLK cycles min
kSPS max
V min/max
µA max
µA typ
µA typ
µA typ
µA typ
µA max
mW max
mW typ
µW max
Functional from 2.2 V to 5.25 V
Digital I/Ps = 0 V or V
CC
Internal reference off, V
CC
= 3.6 V, 240 µA typ
Internal reference on, V
CC
= 3.6 V
Internal reference off, V
CC
= 2.7 V, f
DCLK
= 200 kHz
Internal reference off, V
CC
= 3.6 V
Internal reference on, V
CC
= 3.6 V
200 nA typ
Internal reference off, V
CC
= 3.6 V
Internal reference on, V
CC
= 3.6 V
V
CC
= 3.6 V
12
3
125
2.7/3.6
380
670
170
150
580
1
1.368
2.412
3.6
Temperature range as follows: A, B Versions: –40°C to +85°C.
See the Terminology section.
3
Difference between TEMP0 and TEMP1 measurement. No calibration necessary.
4
Temperature drift is –2.1 mV/°C.
5
Sample tested @ 25°C to ensure compliance.
6
See the Power vs. Throughput Rate section.
Rev. F | Page 4 of 28
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