ADT70GN Analog Devices Inc, ADT70GN Datasheet - Page 12

• Manufacturer Part Number: ADT70GN
• Manufacturer: Analog Devices Inc

Specifications of ADT70GN

• Operating Temperature (min): -40C
• Operating Temperature (max): 125C
• Operating Temperature Classification: Automotive
• Mounting: Through Hole
• Pin Count: 20
• Package Type: PDIP
• Lead Free Status / RoHS Status: Not Compliant

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
A 1000
ten times the scale of the 100
has been designed to allow for 1000
sors. Only the gain setting resistor RG needs to be altered. For
PRTD Application Circuit
PRTD sensor scales by 3.85 s/ C, which is exactly
NODE D
1k
PRTD
10 F
Figure 31. Single Supply Application with an ADR290 “Pseudo-Ground”
1k
REF
RESISTOR
PRTD sensor. The ADT70
+5V
0.1 F
NODE C
49.9k
or 100
IN
ADR290
RG
RG
GND
I
I
+IN
OUTB
OUTA
OUT
IN
NULLA
IA
IA
PRTD sen-
0.1 F
NULLB
INST
AMP
SOURCES
MATCHED
CURRENT
GND
SENSE
BIAS
–12–
OUT
a 100
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.
Figure 32. 100
New Value for RG
2.5V
2.5V
REF
REFOUT
AGND
PRTD 0.00385 sensor, change RG to 4.99 k as illus-
4.99k
V
ADT70
S
DOWN
SHUT-
+IN
DGND
IN
0.00385 PRTD Application Showing
RG
RG
IA
IA
+5V
SHUTDOWN
+V
OUT
+IN
INST
AMP
IN
S
OA
OA
OA
GND
SENSE
OUT
REV. 0