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FEATURES
16-Bit - ADC
Programmable Gain Front End
Simultaneous 50 Hz and 60 Hz Rejection at 20 Hz
Update Rate
VREF Select™
Allows Absolute and Ratiometric
Measurement Capability
ISOURCE Select™
16-Bit No Missing Codes
13-Bit p-p Resolution @ 20 Hz, 20 mV Range
16-Bit p-p Resolution @ 20 Hz, 2.56 V Range
INTERFACE
3-Wire Serial
SPI
®
, QSPI™, MICROWIRE™, and DSP Compatible
Schmitt Trigger on SCLK
POWER
Specified for Single 3 V and 5 V Operation
Normal: 1.25 mA Typ @ 3 V
Power-Down: 7 A (32.768 kHz Crystal Running)
ON-CHIP FUNCTIONS
Rail-to-Rail Input Buffer and PGA
Selectable Reference Inputs
3 Switchable, Ratioed Current Sources for
V
BE
Measurements
4-Bit Digital I/O Port
Low-Side Power Switches
16-Bit - ADC with
Switchable Current Sources
AD7709
APPLICATIONS
Sensor Measurement
Temperature Measurement
Pressure Measurements
Weigh Scales
Portable Instrumentation
4–20 mA Loops
GENERAL DESCRIPTION
The AD7709 is a complete analog front end for low frequency
measurement applications. It contains a 16-bit - ADC, selectable
reference inputs, three switchable matched excitation current
sources, low-side power switches, and a digital I/O port. The
16-bit channel with PGA accepts fully differential, unipolar,
and bipolar input signal ranges from 1.024 REFIN/128 to
1.024 REFIN. It can be configured as two fully differential
input channels or four pseudo-differential input channels. Signals
can be converted directly from a transducer without the need for
signal conditioning.
The device operates from a 32.768 kHz crystal with an on-chip
PLL generating the required internal operating frequency. The
output data rate from the part is software programmable. The
p-p resolution from the part varies with the programmed gain
and output data rate.
The part operates from a single 3 V or 5 V supply. When
operating from 3 V supplies, the power dissipation for the part
is 3.75 mW. The AD7709 is housed in a 24-lead TSSOP package.
FUNCTIONAL BLOCK DIAGRAM
REFIN1(+) REFIN2(+)
V
DD
IEXC1
8I
IOUT1
IEXC2
8I
IEXC3
I
OSCILLATOR
AND
PLL
REFIN1(–) REFIN2(–)
XTAL1
XTAL2
DOUT
IOUT2
AIN1
AIN2
AIN3/P3
AIN4/P4
AINCOM
I = 25 A
SERIAL
INTERFACE
AND
CONTROL
LOGIC
V
DD
I/O PORT
DIN
SCLK
CS
RDY
RESET
MUX
BUF
PGA
16-BIT - ADC
AD7709
V
DD
GND
PWRGND
P1/SW1 P2/SW2
REV. A
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. 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 companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© 2003 Analog Devices, Inc. All rights reserved.
AD7709
TABLE OF CONTENTS
FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . 1
FUNCTIONAL BLOCK DIAGRAM . . . . . . . . . . . . . . . . . 1
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
TIMING CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . 6
ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . 8
ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
PIN CONFIGURATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
PIN FUNCTION DESCRIPTIONS . . . . . . . . . . . . . . . . . . 9
TYPICAL PERFORMANCE CHARACTERISTICS . . . . 10
ADC CIRCUIT INFORMATION . . . . . . . . . . . . . . . . . . . 11
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
S-D
ADC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
NOISE PERFORMANCE . . . . . . . . . . . . . . . . . . . . . . . . . 13
ON-CHIP REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Communications Register . . . . . . . . . . . . . . . . . . . . . . . . 14
Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Configuration Register . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Filter Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
ADC Data Result Register . . . . . . . . . . . . . . . . . . . . . . . . 18
CONFIGURING THE AD7709 . . . . . . . . . . . . . . . . . . . . . 19
DIGITAL INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
MICROCOMPUTER/MICROPROCESSOR
INTERFACING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
AD7709-to-68HC11 Interface . . . . . . . . . . . . . . . . . . . . .
AD7709-to-8051 Interface . . . . . . . . . . . . . . . . . . . . . . . .
AD7709-to-ADSP-2103/ADSP-2105 Interface . . . . . . . .
CIRCUIT DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . .
Analog Input Channels . . . . . . . . . . . . . . . . . . . . . . . . . .
Programmable Gain Amplifier . . . . . . . . . . . . . . . . . . . . .
Bipolar/Unipolar Configuration . . . . . . . . . . . . . . . . . . . .
Data Output Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Excitation Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Crystal Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reference Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reset Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power-Down Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Grounding and Layout . . . . . . . . . . . . . . . . . . . . . . . . . . .
APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pressure Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . .
Temperature Measurement . . . . . . . . . . . . . . . . . . . . . . .
3-Wire RTD Configurations . . . . . . . . . . . . . . . . . . . . . .
Smart Transmitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . .
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
21
21
21
22
22
23
23
23
24
24
24
24
24
24
25
25
26
27
28
29
30
–2–
REV. A
AD7709
SPECIFICATIONS
Parameter
1
(V
DD
= 2.7 V to 3.6 V or 4.75 V to 5.25 V, REFIN(+) = 2.5 V; REFIN(–) = GND; GND = 0 V; XTAL1/XTAL2 =
32.768 kHz Crystal; all specifications T
MIN
to T
MAX
, unless otherwise noted.)
AD7709A, AD7709B
5.4
105
16
13
16
See Tables II to V
±
30
±
3
±
10
±
0.75
±
0.2
±
0.5
85
±
1.024
¥
REFIN
GAIN
Unit
Hz min
Hz max
Bits min
Bits p-p
Bits p-p
ppm of FSR max
mV
typ
nV/∞C typ
LSB typ
% of FS typ
ppm/∞C typ
dB typ
Test Conditions
0.732 ms Increments
ADC CHANNEL SPECIFICATION
Output Update Rate
ADC CHANNEL
No Missing Codes
2
Resolution
Output Noise and Update Rates
Integral Nonlinearity
2
Offset Error
Offset Error Drift vs. Temperature
Full-Scale Error
3
Gain Drift vs. Temperature
Power Supply Rejection (PSR)
ANALOG INPUTS
Differential Input Voltage Ranges
ADC Range Matching
Absolute AIN1–AIN4 Voltage Limits
2
AIN1–AIN4 Analog Input Current
DC Input Current
2
DC Input Current Drift
Absolute AINCOM Voltage Limits
2
AINCOM Analog Input Current
DC Input Current
DC Input Current Drift
Normal-Mode Rejection
2, 4
@ 50 Hz
@ 60 Hz
Common-Mode Rejection
@ DC
@ 50 Hz
2
@ 60 Hz
2
REFERENCE INPUTS
(REFIN1 and REFIN2)
REFIN Voltage
REFIN Voltage Range
2
Absolute REFIN Voltage Limits
2
Average Reference Input Current
Average Reference Input Current Drift
Normal-Mode Rejection
2, 4
@ 50 Hz
@ 60 Hz
Common-Mode Rejection
@ DC
@ 50 Hz
@ 60 Hz
See Notes on page 5.
20 Hz Update Rate
±
20 mV Range, 20 Hz Update Rate
±
2.56 V Range, 20 Hz Update Rate
Typically 2 ppm
FSR
=
B Grade, V
DD
= 4 V
A Grade
Input Range =
±
2.56 V
100 dB typ on
±
20 mV Range
REFIN = REFIN(+) – REFIN(–)
GAIN = 1 to 128
Input Voltage = 19 mV on All Ranges
2
¥
1.024
REFIN
GAIN
V nom
mV
typ
V min
V max
nA max
pA /∞C typ
V min
V max
nA/V typ
pA/V/∞C typ
dB min
dB min
dB typ
dB min
dB min
±
2
GND + 100 mV
V
DD
– 100 mV
±
1
±
5
GND – 30 mV
V
DD
+ 30 mV
±
125
±
2
100
100
100
100
100
Pseudo-Differential Mode of Operation
Input Current Varies with Input Range
50 Hz
±
1 Hz, 16.65 Hz Update Rate, SF = 82
60 Hz
±
1 Hz, 20 Hz Update Rate, SF = 68
Input Range =
±
2.56 V, AIN = 1 V
110 dB typ on
±
20 mV Range
50 Hz
±
1 Hz, Range =
±
2.56 V, AIN = 1 V
60 Hz
±
1 Hz, Range =
±
2.56 V, AIN = 1 V
2.5
1
V
DD
GND – 30 mV
V
DD
+ 30 mV
0.5
±
0.01
100
100
110
110
110
V nom
V min
V max
V min
V max
mA/V
typ
nA/V/∞C typ
dB min
dB min
dB typ
dB typ
dB typ
REFIN = REFIN(+) – REFIN(–)
50 Hz
±
1 Hz, SF = 82
60 Hz
±
1 Hz, SF = 68
Input Range =
±
2.56 V, AIN = 1 V
50 Hz
±
1 Hz, Range = 2.56 V, AIN = 1 V
60 Hz
±
1 Hz, Range = 2.56 V, AIN = 1 V
REV. A
–3–
AD7709
SPECIFICATIONS
(continued)
Parameter
EXCITATION CURRENT SOURCES
(IEXC1, IEXC2, and IEXC3)
Output Current
IEXC1, IEXC2
IEXC3
Initial Tolerance at 25∞C
Drift
Initial Current Matching at 25∞C
(between IEXC1 and IEXC2)
Drift Matching
(between IEXC1 and IEXC2)
Initial Current Matching at 25∞C
(between 8 IEXC3 and
IEXC1/IEXC2)
Drift Matching
(between 8 IEXC3 and
IEXC1/IEXC2)
Line Regulation
IEXC1, IEXC2
IEXC3
Load Regulation
Output Compliance
LOW-SIDE POWER SWITCHES
(SW1 and SW2)
R
ON
AD7709A, AD7709B
Unit
Test Conditions
200
25
±
10
200
±
2.5
±
2.5
20
±
5
±
5
20
1.25
2.6
1
1
300
V
DD
– 0.6
GND –30 mV
mA
nom
mA
nom
% typ
ppm/∞C typ
% max
% typ
ppm/∞C typ
% max
% typ
B Grade, No Load
A Grade, No Load
B Grade, No Load
A Grade, No Load
ppm/∞C typ
mA/V
typ
mA/V
max
mA/V
max
mA/V
typ
nA/V typ
V max
V min
V
DD
= 5 V
±
5%
A, B Grades
B Grade
B Grade
A Grade
Allowable Current
2
LOGIC INPUTS
All Inputs Except SCLK and XTAL1
2
V
INL
, Input Low Voltage
V
INH
, Input High Voltage
SCLK Only (Schmitt-Triggered Input)
2
V
T(+)
V
T(–)
V
T(+)
– V
T(–)
V
T(+)
V
T(–)
V
T(+)
– V
T(–)
XTAL1 Only
2
V
INL
, Input Low Voltage
V
INH
, Input High Voltage
V
INL
, Input Low Voltage
V
INH
, Input High Voltage
Input Currents (except XTAL)
3
5
4.5
7
20
W
typ
W
max
W
typ
W
max
mA max
V
DD
= 5 V, A and B Grade
B Grade
V
DD
= 3 V, A and B Grade
B Grade
Continuous Current per Switch
0.8
0.4
2.0
1.4/2
0.8/1.4
0.3/0.85
0.95/2
0.4/1.1
0.3/0.85
0.8
3.5
0.4
2.5
±
2
–70
V max
V max
V min
V min/V max
V min/V max
V min/V max
V min/V max
V min/V max
V min/V max
V max
V min
V max
V min
mA
max
mA
max
pF typ
V
DD
= 5 V
V
DD
= 3 V
V
DD
= 3 V or 5 V
V
DD
= 5 V
V
DD
= 5 V
V
DD
= 5 V
V
DD
= 3 V
V
DD
= 3 V
V
DD
= 3 V
V
DD
= 5 V
V
DD
= 5 V
V
DD
= 3 V
V
DD
= 3 V
V
IN
= V
DD
V
IN
= GND, Typically –40
mA
@ 5 V and
–20
mA
at 3 V; Weak Pull-Ups on the
Logic Inputs
All Digital Inputs
Input Capacitance
10
–4–
REV. A
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