ADT70GR-REEL7 Analog Devices Inc, ADT70GR-REEL7 Datasheet - Page 11

• Manufacturer Part Number: ADT70GR-REEL7
• Manufacturer: Analog Devices Inc

Specifications of ADT70GR-REEL7

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

REV. 0
achieve in a single supply application where the negative rail is
ground or 0 V. Therefore, to achieve full scale operation the
output of ADT70 should be shifted by 1 V to allow for opera-
tion in the 0 V to 5 V region.
The most straightforward method to shift the output voltage
incorporates the use of the GND SENSE as shown in Figure 29.
To shift output voltage range apply a potential equal to the neces-
sary shift on the GND SENSE pin. For example, to shift the out-
put voltage, OUT
GND SENSE. When applying a potential to GND SENSE, care
should be taken to ensure that the voltage source is capable of driv-
ing 2 k and does not introduce excessive noise. Figure 29 uses the
on-board 2.5 V voltage reference for a low noise source. This refer-
ence is then divided to 1 V and buffered by the on-board op amp
to drive GND SENSE at a low impedance. A small 500
ometer can be used to calibrate the initial offset error to zero.
IA
Figure 30. A Basic Single Supply Operational Diagram with Bias Resistor in Sensor Path
, up to 1 V to GND SENSE, apply 1 V to
RESISTOR
1k
PRTD
SENSOR
768
RESISTOR
1K
PRTD
1k
REF
Figure 29. A Single Supply Application with Shifted Ground Sense Pin
1K
REF
RESISTOR
49.9k
49.9k
RG
RG
RG
RG
I
I
+IN
OUTB
OUTA
I
I
+IN
OUTB
OUTA
IN
NULLA
IN
NULLA
IA
IA
IA
IA
NULLB
INST
AMP
NULLB
INST
AMP
SOURCES
MATCHED
CURRENT
SOURCES
MATCHED
CURRENT
GND
SENSE
GND
SENSE
potenti-
BIAS
BIAS
OUT
–11–
IA
2.5V
2.5V
However, a voltage applied to GND SENSE is not the only
method to shift the voltage range. Placing a 768
PRTD sensor path also shifts the output voltage by 1 V. This
second method, as shown in Figure 30, is usually not recom-
mended for the following reasons; the input voltage range of the
op amps is limited to around 1 V from the negative and positive
rails and this could cause problems at high temperature, limiting
the upper range to 600 C; the physical location of this resistor
(if placed at a distance from the ADT70) may have an impact
on the noise performance. The method frees up the on-board op
amp for another function and achieves the lowest impedance
ground point for GND SENSE.
This brief section on ADT70 single supply operation has focused
on simple techniques to bias the ADT70 such that all output volt-
ages are within operational range. However, these techniques may
not be useful in all single supply applications. For example, in Fig-
ure 3 the additional on-board op amp is operating at near ground
potential which will create problems in a single supply application
2.5V
REF
2.5V
REFOUT
REF
TO A/D CONVERTER
REFOUT
+5V
V
S
DOWN
SHUT-
DOWN
SHUT-
ADT70
DGND
DGND
ADT70
SHUTDOWN
+V
OUT
+IN
SHUTDOWN
+V
OUT
+IN
IN
S
IN
OA
S
OA
OA
OA
OA
OA
TO CONTROLLER
TO CONTROLLER
15k
9.76k
500
POT
V
REF
ADT70
resistor in the