ADT7485AARMZ-R View Datasheet(PDF) - ON Semiconductor
Part Name
Description
Manufacturer
ADT7485AARMZ-R Datasheet PDF : 12 Pages
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ADT7485A
• Use wide tracks to minimize inductance and reduce
noise pickup. A 5 mil track minimum width and
spacing is recommended.
GND
D1+
D1–
GND
5mil
5mil
5mil
5mil
5mil
5mil
5mil
Figure 17. Arrangements of Signal Tracks
• Try to minimize the number of copper/solder joints,
which can cause thermocouple effects. Where
copper/solder joints are used, make sure that they are in
both the D1+ and D1− paths and are at the same
temperature.
• Thermocouple effects should not be a major problem
because 1°C corresponds to about 240 mV, and
thermocouple voltages are about 3 mV/°C of the
temperature difference. Unless there are two
thermocouples with a big temperature differential
between them, thermocouple voltages should be much
less than 200 mV.
• Place a 0.1 mF bypass capacitor close to the ADT7485A.
• 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.
• 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 D+ and D−
and the shield to GND, close to the ADT7485A. 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 using long cables, the
filter capacitor can be reduced or removed. Cable resistance
can also introduce errors. A 1 W series resistance introduces
about 0.5°C error.
Temperature Offset
As CPUs run faster, it is more difficult to avoid high
frequency clocks when routing the D+ and D− tracks around
a system board. Even when the recommended layout
guidelines are followed, there may still be temperature
errors, attributed to noise being coupled onto the D+ and D−
lines. High frequency noise generally has the effect of
producing temperature measurements that are consistently
too high by a specific amount. The ADT7485A has
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 ADT7485A.
The offset is automatically added to every temperature
measurement. The maximum offset is ±128°C with 0.25°C
resolution. The offset format is the same as the temperature
data format; 16−bit, twos complement notation, as shown in
Table 11. 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.
ORDERING INFORMATION
Device Order Number*
Package Type
Package Option
Shipping†
ADT7485AARMZ−R
ADT7485AARMZ−R7
10−Lead MSOP
RM−10
3000 Tape & Reel
1000 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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