ADT7461AR-REEL7 ON Semiconductor, ADT7461AR-REEL7 Datasheet - Page 20

• Manufacturer Part Number: ADT7461AR-REEL7
• Description: IC SENSOR TEMP 2-CH 8SOIC
• Manufacturer: ON Semiconductor

Specifications of ADT7461AR-REEL7

• Rohs Status: RoHS non-compliant
• Function: Temp Monitoring System (Sensor)
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: 0°C ~ 127°C, External Sensor
• Output Type: SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 120°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)

ADT7461
thermal, contact with a PCB and may also be in a forced airflow.
How accurately the temperature of the board and/or the forced
airflow reflects the temperature to be measured also affects the
accuracy. Self-heating due to the power dissipated in the
ADT7461 or the remote sensor causes the chip temperature of
the device or remote sensor to rise above ambient.
However, the current forced through the remote sensor is so
small that self-heating is negligible. With the ADT7461, the
worst-case condition occurs when the device is converting at 64
conversions per second while sinking the maximum current of
1 mA at the ALERT and THERM output. In this case, the total
power dissipation in the device is about 4.5 mW. The thermal
resistance, θ
LAYOUT CONSIDERATIONS
Digital boards can be electrically noisy environments, and the
ADT7461 is measuring very small voltages from the remote
sensor, so care must be taken to minimize noise induced at the
sensor inputs. The following precautions should be taken:
1.
2.
GND
GND
D+
D–
Place the ADT7461 as close as possible to the remote
sensing diode. Provided the worst noise sources, such as
clock generators, data/address buses, and CRTs, are
avoided, this distance can be 4 inches to 8 inches.
Route the D+ and D– tracks close together, in parallel, with
grounded guard tracks on each side. To minimize
inductance and reduce noise pick-up, a 5 mil track width
and spacing is recommended. Provide a ground plane
under the tracks if possible.
JA
Figure 24. Typical Arrangement of Signal Tracks
, of the SOIC-8 package is about 121°C/W.
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5MIL
5MIL
5MIL
5MIL
5MIL
5MIL
5MIL
3.
4.
5.
Because the measurement technique uses switched current
sources, excessive cable or filter capacitance can affect the
measurement. When using long cables, the filter capacitance
may be reduced or removed.
Try to minimize the number of copper/solder joints
that can cause thermocouple effects. Where copper/solder
joints are used, make sure that they are in both the D+ and
D− path and at the same temperature.
Thermocouple effects should not be a major problem as
1°C corresponds to about 200 mV, and thermocouple
voltages are about 3 mV/°C of 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 μF bypass capacitor close to the V
extremely noisy environments, an input filter capacitor
may be placed across D+ and D− close to the ADT7461.
This capacitance can effect the temperature measurement,
so care must be taken to ensure any capacitance seen at D+
and D− is a maximum of 1,000 pF. This maximum value
includes the filter capacitance plus any cable or stray
capacitance between the pins and the sensor diode.
If the distance to the remote sensor is more than 8 inches,
the use of twisted pair cable is recommended. This works
up to about 6 feet to 12 feet.
For extremely long distances (up to 100 feet), use a
shielded twisted pair, such as the Belden No. 8451
microphone cable. Connect the twisted pair to D+ and D−
and the shield to GND close to the ADT7461. Leave the
remote end of the shield unconnected to avoid ground
loops.
DD
pin. In