OMO ElectronicOMO Electronic
Expand menu
Hello, Sign inMy Account
0 Cart

ADT7484AARMZ-RL

P1-P3P4-P6P7-P9P10-P12P13-P14
ADT7484A/ADT7486A
http://onsemi.com
10
Reading Temperature Measurements
The temperature measurement command codes are
detailed in Table 12. The temperature data returned is two
bytes in little endian format, that is, LSB before MSB. All
temperatures can be read together by using Command Code
0x00 with a read length of 0x04. The command codes and
returned data are described in Table 12.
Table 12. TEMPERATURE CHANNEL COMMAND
CODES
Temp
Channel
Command
Code
Returned Data
Internal 0x00 LSB, MSB
External 1 0x01 LSB, MSB
External 2 0x02 LSB, MSB
All Temps 0x00 Internal LSB, Internal MSB;
External 1 LSB, External 1 MSB;
External 2 LSB, External 2 MSB
SST Temperature Sensor Data Format
The data for temperature is structured to allow values in
the range of 512C to be reported. Thus, the temperature
sensor format uses a twos complement, 16-bit binary value
to represent values in this range. This format allows
temperatures to be represented with approximately a
0.016C resolution.
Table 13. SST TEMPERATURE DATA FORMAT
Temperature (5C)
Twos Complement
MSB LSB
−125 1110 0000 1100 0000
−80 1110 1100 0000 0000
−40 1111 0110 0000 0000
−20 1111 1011 0011 1110
−5 1111 1110 1100 0000
−1 1111 1111 1100 0000
0 0000 0000 0000 0000
+1 0000 0000 0100 0000
+5 0000 0001 0100 0000
+20 0000 0100 1100 0010
+40 0000 1010 0000 0000
+80 0001 0100 0000 0000
+125 0001 1111 0100 0000
Using Discrete Transistors
If a discrete transistor is used, the collector is not grounded
and should be linked to the base. If a PNP transistor is used,
the base is connected to the D1− input and the emitter is
connected to the D1+ input. If an NPN transistor is used, the
emitter is connected to the D1− input and the base is
connected to the D1+ input. Figure 17 shows how to connect
the ADT7484A/ADT7486A to an NPN or PNP transistor for
temperature measurement. To prevent ground noise from
interfering with the measurement, the more negative
terminal of the sensor is not referenced to ground, but is
biased above ground by an internal diode at the D1− input.
Figure 15. Connections for NPN and PNP Transistors
ADT7484A/
ADT7486A
D+
D−
2N3904
NPN
ADT7484A/
ADT8486A
D+
D−
2N3906
PNP
The ADT7484A/ADT7486A show an external
temperature value of 0x8000 if the external diode is an open
or short circuit.
Layout Considerations
Digital boards can be electrically noisy environments.
Take the following precautions to protect the analog inputs
from noise, particularly when measuring the very small
voltages from a remote diode sensor:
1. Place the device as close as possible to the remote
sensing diode. Provided that the worst noise
sources, such as clock generators, data/address
buses, and CRTs, are avoided, this distance can be
four to eight inches.
2. Route the D1+ and D1− tracks close together in
parallel with grounded guard tracks on each side.
Provide a ground plane under the tracks if
possible.
3. Use wide tracks to minimize inductance and
reduce noise pickup. A 5 mil track minimum width
and spacing is recommended.
Figure 16. Arrangement of Signal Tracks
5 MIL
5 MIL
5 MIL
5 MIL
5 MIL
5 MIL
5 MIL
GND
D−
D+
GND
4. 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.
5. Thermocouple effects should not be a major
problem because 1C corresponds to about
240 mV, and thermocouple voltages are about
3 mV/C of the temperature difference. Unless
ADT7484A/ADT7486A
http://onsemi.com
11
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
Figure 17. ADT7484A Typical Application Schematic
RESERVED
SST
ADD0
ADD1
V
CC
GND
D1+
D1−
8
7
6
54
3
2
1
ADT7484A
SST
V
CC
2N3904
or
CPU
THERMAL
DIODE
Figure 18. ADT7486A Typical Application Schematic
RESERVED
SST
ADD0
ADD1
V
CC
GND
D1+
D1−
10
9
8
74
3
2
1
ADT7486A
SST
V
CC
2N3904
NPN
D2−D2+ 65
CPU
THERMAL
DIODE
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.
ADT7484A/ADT7486A
http://onsemi.com
12
PACKAGE DIMENSIONS
SOIC−8 NB
CASE 751−07
ISSUE AK
SEATING
PLANE
1
4
58
N
J
X 45
_
K
NOTES:
1. DIMENSIONING AND TOLERANCING PER
ANSI Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DIMENSION A AND B DO NOT INCLUDE
MOLD PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 (0.006)
PER SIDE.
5. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.127 (0.005) TOTAL
IN EXCESS OF THE D DIMENSION AT
MAXIMUM MATERIAL CONDITION.
6. 751−01 THRU 751−06 ARE OBSOLETE. NEW
STANDARD IS 751−07.
A
B
S
D
H
C
0.10 (0.004)
DIM
A
MIN MAX MIN MAX
INCHES
4.80 5.00 0.189 0.197
MILLIMETERS
B 3.80 4.00 0.150 0.157
C 1.35 1.75 0.053 0.069
D 0.33 0.51 0.013 0.020
G 1.27 BSC 0.050 BSC
H 0.10 0.25 0.004 0.010
J 0.19 0.25 0.007 0.010
K 0.40 1.27 0.016 0.050
M 0 8 0 8
N 0.25 0.50 0.010 0.020
S 5.80 6.20 0.228 0.244
−X−
−Y−
G
M
Y
M
0.25 (0.010)
−Z−
Y
M
0.25 (0.010) Z
S
X
S
M
____
1.52
0.060
7.0
0.275
0.6
0.024
1.270
0.050
4.0
0.155
ǒ
mm
inches
Ǔ
SCALE 6:1
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
SOLDERING FOOTPRINT*
P1-P3P4-P6P7-P9P10-P12P13-P14

ADT7484AARMZ-RL

Mfr. #:
Buy ADT7484AARMZ-RL
Manufacturer:
ON Semiconductor
Description:
Board Mount Temperature Sensors DIGITAL TEMP SENSOR W/SST INTERFACE
Lifecycle:
New from this manufacturer.
Delivery:
DHL FedEx Ups TNT EMS
Payment:
T/T Paypal Visa MoneyGram Western Union

Products related to this Datasheet