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ADT70GN Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADT70GN
Beschreibung PRTD Conditioning Circuit and Temperature Controller
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 14 Seiten
ADT70GN Datasheet, Funktion
a
PRTD Conditioning Circuit
and Temperature Controller
ADT70*
FEATURES
PRTD Temperature Measurement Range
Typical IC Measurement Error ؎1؇C
Includes Two Matched Current Sources
Rail-to-Rail Output Instrumentation Amp
Uncommitted, Rail-to-Rail Output Op Amp
On-Board ؉2.5 V Reference
Temperature Coefficient ؎25 ppm/؇C
؉5 V or ؎5 V Operation
Supply Current 4 mA Max
10 A Max in Shutdown
APPLICATIONS
Temperature Controllers
Portable Instrumentation
Temperature Acquisition Cards
GENERAL DESCRIPTION
The ADT70 provides excitation and signal conditioning for
resistance-temperature devices (RTDs). It is ideally suited for
1 kPlatinum RTDs (PRTDs), allowing a very wide range of
temperature measurement. It can also easily interface to 100
PRTDs. Using a remote, low cost thin-film PRTD, the ADT70
can measure temperature in the range of –50°C to +500°C.
With high performance platinum elements, the temperature
change can be extended to 1000°C. Accuracy of the ADT70
and PRTD system over a –200°C to +1000°C temperature
range heavily depends on the quality of the PRTD. Typically
the ADT70 will introduce an error of only ± 1°C over the
transducer's temperature range, and the error may be trimmed
to zero at a single calibration point.
The ADT70 consists of two matched 1 mA (nominal) current
sources for transducer and reference resistor excitation, a preci-
sion rail-to-rail output instrumentation amplifier, a 2.5 V refer-
ence and an uncommitted rail-to-rail output op amp. The
ADT70 includes a shutdown function for battery powered
equipment, which reduces the quiescent current from 4 mA to
less than 10␣ µA. The ADT70 operates from either single +5 V
or ±5 V supplies. Gain or full-scale range for the PRTD and
ADT70 system is set by a precision external resistor connected
to the instrumentation amplifier. The uncommitted op amp may
be used for scaling the internal voltage reference, providing a
“PRTD open” signal or “over-temperature” warning, a heater
switching signal, or other external conditioning determined by
the user.
The ADT70 is specified for operation from ؊40°C to ؉125°C
and is available in 20-lead DIP and SO packages.
*Patent pending.
REV. 0
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
FUNCTIONAL BLOCK DIAGRAM
NULLA NULLB BIAS 2.5VREFOUT
IOUTA
IOUTB
MATCHED
CURRENT
SOURCES
2.5V
REF
ADT70
+VS
OUTOA
+INOA
؊INOA
+INIA
؊INIA
INST
AMP
SHUT-
DOWN
RGA RGB GND
SENSE
OUTIA AGND ؊VS DGND
PIN CONFIGURATIONS
20-Lead P-DIP
(N Suffix)
–VS 1
20 +VS
AGND 2
19 VOUT OA
VREFOUT 3
18 –INOA
BIAS 4
17 +INOA
NULLA 5 ADT70 16 SHUTDOWN
TOP VIEW
NULLB 6 (Not to Scale) 15 DGND
IOUTA 7
14 VOUT IA
IOUTB 8
13 GND SENSE
–INIA 9
12 RGB
+INIA 10
11 RGA
a
20-Lead SOIC
(R Suffix)
–VS 1
AGND 2
20 +VS
19 VOUT OA
VREFOUT 3
BIAS 4
18 –INOA
17 +INOA
NULLA 5 ADT70 16 SHUTDOWN
TOP VIEW
NULLB 6 (Not to Scale) 15 DGND
IOUTA 7
IOUTB 8
؊ INIA 9
؉ INIA 10
14 VOUT IA
13 GND SENSE
12 RGB
11 RGA
a
SHUTDOWN
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., 1998






ADT70GN Datasheet, Funktion
ADT70
1000
VCC = 5V
VEE = 0
TA = +25؇C
100
VCC,
SOURCING
CURRENT
10
VEE,
SINKING
CURRENT
1
1 10 100 1k 10k
LOAD CURRENT – A
Figure 13. Op Amp Output Voltage from Rails vs.
Load Current
2.52
2.515
2.51
VS = +5V, DUT SOURCING
2.505
2.5
2.495
2.49
2.485
2.48
0
12
345678
LOAD CURRENT – mA
9
Figure 14. Reference Voltage vs. Load Current
4
TA = +25؇C
VCM INAMP = 1V
VEE = GND
3.8
3.6
3.4
3.2
3
4.5 4.75 5.0 5.25 5.5
SUPPLY VOLTAGE – Volts
Figure 15. Supply Current vs. Supply Voltage
950
VCC = 5V
VEE = 0V
VREF = 2.5V
940
+125؇C
930
+25؇C
920
؊55؇C
910
4.5
4.75 5.0 5.25
SUPPLY VOLTAGE – Volts
5.5
Figure 16. Output of Current Source vs. Supply Voltage
140
120
100
80
AV = 14
60
AV = 1.4
40
20
0
10 100 1k 10k 100k 1M
FREQUENCY – Hz
Figure 17. In Amp CMRR vs. Frequency
120 270
100 225
80 180
60 135
40 90
20 45
00
؊20
؊45
؊40
؊90
؊60
؊80
100
1k 10k 100k 1M
FREQUENCY – Hz
؊135
؊180
10M
Figure 18. Op Amp Open Loop Gain and Phase vs.
Frequency
–6– REV. 0

6 Page









ADT70GN pdf, datenblatt
ADT70
because the input voltage range of the on-board op amp only ex-
tends to about 1 V above the negative rail. If the application re-
quires the inputs of either the on-board amp or instrumentation
amplifier to operate within 1 V of ground, it will be necessary to
generate a “pseudo-ground.” Figure 31 illustrates a typical
ADT70 “pseudo-ground” application. The Analog Devices’
ADR290, a 2.048 V reference, is being used to generate the
“pseudo-ground.” The ADR290 was selected for the following
reasons: low noise, ability to drive the required 5 mA in this
application, good temperature stability, which is usually impor-
tant in a PRTD application. However, one undesired effect of
introducing the pseudo-ground is the loss in voltage range at
high temperature. In our example, the PRTD will only operate
from –200°C to +400°C corresponding to an input voltage
range of 1 V to 4 V.
100 PRTD Application Circuit
A 1000 PRTD sensor scales by 3.85 s/°C, which is exactly
ten times the scale of the 100 PRTD sensor. The ADT70
has been designed to allow for 1000 or 100 PRTD sen-
sors. Only the gain setting resistor RG needs to be altered. For
a 100 PRTD 0.00385 sensor, change RG to 4.99 kas illus-
trated in Figure 32. In single supply application, with a 100
PRTD sensor, a “pseudo-ground” will be necessary because the
inputs of the instrumentation amplifier will be within 1 V of the
negative rail. See the section on single supply applications for
more information.
؊INIA
RG
4.99k
INST
AMP
RG
+INIA
GND
SENSE
OUT
Figure 32. 100␣ 0.00385 PRTD Application Showing
New Value for RG
NULLA NULLB BIAS
2.5VREFOUT
ADT70
+5V
1k
REF
RESISTOR NODE C
NODE D
IOUTA
IOUTB
MATCHED
CURRENT
SOURCES
1k
PRTD
10F
؊INIA
RG
49.9k
RG
+INIA
+5V
ADR290
IN OUT
0.1F GND
INST
AMP
GND
SENSE
0.1F
2.5V
REF
+VS
OUTOA
+INOA
؊INOA
SHUT-
DOWN
SHUTDOWN
OUT
AGND ؊VS DGND
Figure 31. Single Supply Application with an ADR290 “Pseudo-Ground”
–12–
REV. 0

12 Page





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