ADS7843
FEATURES
q
4-WIRE TOUCH SCREEN INTERFACE
q
RATIOMETRIC CONVERSION
q
SINGLE SUPPLY: 2.7V to 5V
q
UP TO 125kHz CONVERSION RATE
q
SERIAL INTERFACE
q
PROGRAMMABLE 8- OR 12-BIT RESOLUTION
q
2 AUXILIARY ANALOG INPUTS
q
FULL POWER-DOWN CONTROL
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Internet: http://www.burr-brown.com/ FAXLine: (800) 548-6133 (US/Canada Only) Cable: BBRCORP Telex: 066-6491 FAX: (520) 889-1510 Immediate Product Info: (800) 548-6132
DESCRIPTION
The ADS7843 is a 12-bit sampling analog-to-digital
converter (ADC) with a synchronous serial interface
and low on-resistance switches for driving touch
screens. Typical power dissipation is 750
W at a
125kHz throughput rate and a +2.7V supply. The
reference voltage (V
REF
) can be varied between 1V and
+V
CC
, providing a corresponding input voltage range
of 0V to V
REF
. The device includes a shutdown mode
which reduces typical power dissipation to under
0.5
W. The ADS7843 is guaranteed down to 2.7V
operation.
Low power, high speed, and on-board switches make
the ADS7843 ideal for battery operated systems such
as personal digital assistants with resistive touch screens
and other portable equipment. The ADS7843 is avail-
able in a 16-lead SSOP package and is guaranteed
over the 40
C to +85
C temperature range.
APPLICATIONS
q
PERSONAL DIGITAL ASSISTANTS
q
PORTABLE INSTRUMENTS
q
POINT-OF-SALES TERMINALS
q
PAGERS
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TOUCH-SCREEN MONITORS
1997 Burr-Brown Corporation
PDS-1441C
Printed in U.S.A. June, 1998
TOUCH SCREEN CONTROLLER
CDAC
SAR
Comparator
Four
Channel
Multiplexer
Serial
Interface
and
Control
CS
DIN
DOUT
BUSY
DCLK
X+
PENIRQ
X
Y+
Y
IN3
IN4
V
REF
+V
CC
2
ADS7843
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ANALOG INPUT
Full-Scale Input Span
Positive Input - Negative Input
0
V
REF
V
Absolute Input Range
Positive Input
0.2
+V
CC
+0.2
V
Negative Input
0.2
+0.2
V
Capacitance
25
pF
Leakage Current
0.1
A
SYSTEM PERFORMANCE
Resolution
12
Bits
No Missing Codes
11
Bits
Integral Linearity Error
2
LSB
(1)
Offset Error
6
LSB
Offset Error Match
0.1
1.0
LSB
Gain Error
4
LSB
Gain Error Match
0.1
1.0
LSB
Noise
30
Vrms
Power Supply Rejection
70
dB
SAMPLING DYNAMICS
Conversion Time
12
Clk Cycles
Acquisition Time
3
Clk Cycles
Throughput Rate
125
kHz
Multiplexer Settling Time
500
ns
Aperture Delay
30
ns
Aperture Jitter
100
ps
Channel-to-Channel Isolation
V
IN
= 2.5Vp-p at 50kHz
100
dB
SWITCH DRIVERS
On-Resistance
Y+, X+
5
Y, X
6
REFERENCE INPUT
Range
1.0
+V
CC
V
Resistance
CS = GND or +V
CC
5
G
Input Current
13
40
A
f
SAMPLE
= 12.5kHz
2.5
A
CS = +V
CC
0.001
3
A
DIGITAL INPUT/OUTPUT
Logic Family
CMOS
Logic Levels, Except PENIRQ
V
IH
| I
IH
|
+5
A
+V
CC
0.7
+V
CC
+0.3
V
IL
| I
IL
|
+5
A
0.3
+0.8
V
V
OH
I
OH
= 250
A
+V
CC
0.8
V
V
OL
I
OL
= 250
A
0.4
V
PENIRQ
V
OL
T
A
= 0
C to +85
C, 100k
Pull-Up
0.8
V
Data Format
Straight Binary
POWER SUPPLY REQUIREMENTS
+V
CC
Specified Performance
2.7
3.6
V
Quiescent Current
280
650
A
f
SAMPLE
= 12.5kHz
220
A
Shut Down Mode with
3
A
DCLK = DIN = +V
CC
Power Dissipation
+V
CC
= +2.7V
1.8
mW
TEMPERATURE RANGE
Specified Performance
40
+85
C
SPECIFICATIONS
At T
A
=40
C to +85
C, +V
CC
= +2.7V, V
REF
= +2.5V, f
SAMPLE
= 125kHz, f
CLK
= 16 f
SAMPLE
= 2MHz, 12-bit mode, and digital inputs = GND or +V
CC
, unless
otherwise noted.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
ADS7843E
NOTE: (1) LSB means Least Significant Bit. With V
REF
equal to +2.5V, one LSB is 610
V.
3
ADS7843
1
2
3
4
5
6
7
8
+V
CC
X+
Y+
X
Y
GND
IN3
IN4
DCLK
CS
DIN
BUSY
DOUT
PENIRQ
+V
CC
V
REF
16
15
14
13
12
11
10
9
ADS7843
PIN CONFIGURATION
Top View
SSOP
PIN DESCRIPTION
PIN
NAME
DESCRIPTION
1
+V
CC
Power Supply, 2.7V to 5V.
2
X+
X+ Position Input. ADC input Channel 1.
3
Y+
Y+ Position Input. ADC input Channel 2.
4
X
X Position Input.
5
Y
Y Position Input.
6
GND
Ground
7
IN3
Auxiliary Input 1. ADC input Channel 3.
8
IN4
Auxiliary Input 2. ADC input Channel 4.
9
V
REF
Voltage Reference Input
10
+V
CC
Power Supply, 2.7V to 5V.
11
PENIRQ
Pen Interrupt. Open anode output (requires 10k
to 100k
pull-up resistor externally).
12
DOUT
Serial Data Output. Data is shifted on the falling
edge of DCLK. This output is high impedance
when CS is HIGH.
13
BUSY
Busy Output. This output is high impedance when
CS is HIGH.
14
DIN
Serial Data Input. If CS is LOW, data is latched on
rising edge of DCLK.
15
CS
Chip Select Input. Controls conversion timing and
enables the serial input/output register.
16
DCLK
External Clock Input. This clock runs the SAR con-
version process and synchronizes serial data I/O.
ABSOLUTE MAXIMUM RATINGS
(1)
+V
CC
to GND ........................................................................ 0.3V to +6V
Analog Inputs to GND ............................................ 0.3V to +V
CC
+ 0.3V
Digital Inputs to GND ............................................. 0.3V to +V
CC
+ 0.3V
Power Dissipation .......................................................................... 250mW
Maximum Junction Temperature ................................................... +150
C
Operating Temperature Range ........................................ 40
C to +85
C
Storage Temperature Range ......................................... 65
C to +150
C
Lead Temperature (soldering, 10s) ............................................... +300
C
NOTE: (1) Stresses above those listed under "Absolute Maximum Ratings"
may cause permanent damage to the device. Exposure to absolute maximum
conditions for extended periods may affect device reliability.
ELECTROSTATIC
DISCHARGE SENSITIVITY
This integrated circuit can be damaged by ESD. Burr-Brown
recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and
installation procedures can cause damage.
ESD damage can range from subtle performance degradation to
complete device failure. Precision integrated circuits may be
more susceptible to damage because very small parametric
changes could cause the device not to meet its published specifi-
cations.
MAXIMUM
INTEGRAL
PACKAGE
SPECIFICATION
LINEARITY
DRAWING
TEMPERATURE
ORDERING
TRANSPORT
PRODUCT
ERROR (LSB)
PACKAGE
NUMBER
(1)
RANGE
NUMBER
(2)
MEDIA
ADS7843E
2
16-Lead SSOP
322
40
C to +85
C
ADS7843E
Rails
"
"
"
"
"
ADS7843E/2K5
Tape and Reel
NOTES: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. (2) Models with a slash (/) are
available only in Tape and Reel in the quantities indicated (e.g., /2K5 indicates 2500 devices per reel). Ordering 2500 pieces of "ADS7843E/2K5" will get a single
2500-piece Tape and Reel. For detailed Tape and Reel mechanical information, refer to Appendix B of Burr-Brown IC Data Book.
PACKAGE/ORDERING INFORMATION
4
ADS7843
TYPICAL PERFORMANCE CURVES
At T
A
= +25
C, +V
CC
= +2.7V, V
REF
= +2.5V, f
SAMPLE
= 125kHz, and f
CLK
= 16 f
SAMPLE
= 2MHz, unless otherwise noted.
SUPPLY CURRENT vs TEMPERATURE
20
40
100
20
0
40
Temperature (C)
Supply Current (
A)
400
350
300
250
200
150
100
60
80
POWER DOWN SUPPLY CURRENT
vs TEMPERATURE
20
40
100
20
0
40
Temperature (C)
Supply Current (nA)
140
120
100
80
60
40
20
60
80
SUPPLY CURRENT vs +V
CC
3.5
2
5
2.5
4
+V
CC
(V)
Supply Current (
A)
320
300
280
260
240
220
200
180
4.5
3
f
SAMPLE
= 12.5kHz
V
REF
= +V
CC
MAXIMUM SAMPLE RATE vs +V
CC
3.5
2
5
2.5
4
+V
CC
(V)
Sample Rate (Hz)
1M
100k
10k
1k
4.5
3
V
REF
= +V
CC
CHANGE IN GAIN vs TEMPERATURE
20
40
100
20
0
40
Temperature (C)
Delta from +25C (LSB)
0.15
0.10
0.05
0.00
0.05
0.10
0.15
60
80
CHANGE IN OFFSET vs TEMPERATURE
20
40
100
20
0
40
Temperature (C)
Delta from +25C (LSB)
0.6
0.4
0.2
0.0
0.2
0.4
0.6
60
80
5
ADS7843
TYPICAL PERFORMANCE CURVES
(CONT)
At T
A
= +25
C, +V
CC
= +2.7V, V
REF
= +2.5V, f
SAMPLE
= 125kHz, and f
CLK
= 16 f
SAMPLE
= 2MHz, unless otherwise noted.
REFERENCE CURRENT vs SAMPLE RATE
75
0
125
25
50
100
Sample Rate (kHz)
Reference Current (
A)
14
12
10
8
6
4
2
0
REFERENCE CURRENT vs TEMPERATURE
20
40
100
20
0
40
Temperature (C)
Reference Current (
A)
18
16
14
12
10
8
6
60
80
SWITCH ON RESISTANCE vs +V
CC
(X+, Y+: +V
CC
to Pin; X, Y: Pin to GND)
3.5
2
5
2.5
X+
Y+
Y
X
4
+V
CC
(V)
R
ON
(
)
1
8
7
6
5
4
3
2
4.5
3
SWITCH ON RESISTANCE vs TEMPERATURE
(X+, Y+: +V
CC
to Pin; X, Y: Pin to GND)
20
40
100
20
X+
Y+
Y
X
40
Temperature (C)
R
ON
(
)
1
8
7
6
5
4
3
2
60
80
0
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
LSB Error
20
40
60
80
100
120
140
160
180
200
Sampling Rate (kHz)
MAXIMUM SAMPLING RATE vs R
IN
INL: R = 2k
INL: R = 500
DNL: R = 2k
DNL: R = 500
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