FUNCTIONAL BLOCK DIAGRAM
RGA RGB
2IN
IA
+IN
IA
INST
AMP
SHUT-
DOWN
GND
SENSE
OUT
IA
AGND DGND2V
S
SHUTDOWN
+IN
OA
2IN
OA
OUT
OA
+V
S
2.5V
REF
I
OUTA
I
OUTB
MATCHED
CURRENT
SOURCES
NULLA NULLB BIAS 2.5V
REFOUT
ADT70
PIN CONFIGURATIONS
20-Lead P-DIP
(N Suffix)
SHUTDOWN
14
13
12
11
17
16
15
20
19
18
10
9
8
1
2
3
4
7
6
5
–V
S
+IN
OA
–IN
OA
V
OUT

OA
+V
S
AGND
V
REFOUT
BIAS
V
OUT

IA
DGND
NULLA
NULLB
I
OUTA
I
OUTB
–IN
IA
+IN
IA
RGA
RGB
GND SENSE
a
ADT70
TOP VIEW
(Not to Scale)
20-Lead SOIC
(R Suffix)
14
13
12
11
17
16
15
20
19
18
10
9
8
1
2
3
4
7
6
5
–V
S
+IN
OA
–IN
OA
V
OUT OA
+V
S
AGND
V
REFOUT
BIAS
V
OUT

IA
DGND
SHUTDOWN
NULLA
NULLB
I
OUTA
I
OUTB
2 IN
IA
1 IN
IA
RGA
RGB
GND SENSE
ADT70
TOP VIEW
(Not to Scale)
a
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.
a
PRTD Conditioning Circuit
and Temperature Controller
ADT70*
FEATURES
PRTD Temperature Measurement Range
Typical IC Measurement Error 618C
Includes Two Matched Current Sources
Rail-to-Rail Output Instrumentation Amp
Uncommitted, Rail-to-Rail Output Op Amp
On-Board 12.5 V Reference
Temperature Coefficient 625 ppm/8C
15 V or 65 V Operation
Supply Current 4 mA Max
10 mA 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 kW Platinum RTDs (PRTDs), allowing a very wide range of
temperature measurement. It can also easily interface to 100 W
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␣ m A. 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 240 C to 1125 C
and is available in 20-lead DIP and SO packages.
*Patent pending.
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