ADT7484A(2012) データシートの表示（PDF） - ON Semiconductor
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ADT7484A Datasheet PDF : 14 Pages
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ADT7484A/ADT7486A
there are two thermocouples with a big
temperature differential between them,
thermocouple voltages should be much less than
200 mV.
6. Place a 0.1 mF bypass capacitor close to the
device.
7. If the distance to the remote sensor is more than
eight inches, the use of a twisted-pair cable is
recommended. This works for distances of about
6 feet to 12 feet.
8. For very long distances (up to 100 feet), use
shielded twisted-pair cables, such as Belden #8451
microphone cables. Connect the twisted-pair cable
to D1+ and D1− and the shield to GND, close to
the device. Leave the remote end of the shield
unconnected to avoid ground loops.
Because the measurement technique uses switched
current sources, excessive cable and/or filter capacitance
can affect the measurement. When usin g long cables, the
filter capacitor can be reduced or removed. Cable resistance
can also introduce errors. A 1ĂW series resistance introduces
about 0.5C error.
Temperature Offset
As CPUs run faster, it is more difficult to avoid high
frequency clocks when running the D1+ and D1− tracks
around a system board. Even when the recommended layout
guidelines are followed, there may still be temperature
errors, attributed to noise being coupled on to the D1+ and
D1− lines. High frequency noise generally has the effect of
producing temperature measurements that are consistently
too high by a specific amount. The ADT7484A/
ADT87486A have a temperature offset command code of
0xe0 through which a desired offset can be set. By doing a
one-time calibration of the system, the offset caused by
system board noise can be calculated and nulled by
specifying it in the ADT7484A/ADT7486A. The offset is
automatically added to every temperature measurement.
The maximum offset is 128C with 0.25C resolution. The
offset format is the same as the temperature data format;
16-bit, twos complement notation, as shown in Table 13.
The offset should be programmed in little endian format,
that is, LSB before MSB. The offset value is also returned
in little endian format when read.
Application Schematics
VCC
ADT7484A
2N3904
or
CPU
THERMAL
DIODE
1 VCC
2 GND
SST 8
ADD0 7
3 D1+ RESERVED 6
4 D1−
ADD1 5
SST
Figure 17. ADT7484A Typical Application Schematic
2N3904
NPN
VCC
ADT7486A
1 VCC
2 GND
SST 10
ADD0 9
3 D1+ RESERVED 8
4 D1−
ADD1 7
5 D2+
D2− 6
SST
CPU
THERMAL
DIODE
Figure 18. ADT7486A Typical Application Schematic
Table 14. ORDERING INFORMATION
Device Order Number*
Branding
Package Option
Package Type
Shipping†
ADT7484AARZ−REEL
−
R−8
SOIC−8 NB
2,500 Tape & Reel
ADT7484AARMZ−RL
T20
RM−8
8-lead MSOP
3,000 Tape & Reel
ADT7486AARMZ−RL
T22
RM−10
10-lead MSOP
3,000 Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
*These are Pb-Free packages.
http://onsemi.com
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