ADT7461AARMZ-002 ON Semiconductor, ADT7461AARMZ-002 Datasheet - Page 17

• Manufacturer Part Number: ADT7461AARMZ-002
• Description: IC TEMP SENSOR DGTL 2CH 8-MSOP
• Manufacturer: ON Semiconductor

Specifications of ADT7461AARMZ-002

• 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 ~ 3.6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Full Temp Accuracy: +/- 2.5 C
• Digital Output - Bus Interface: Serial (2-Wire)
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Temperature Sensor Function: Temp Sensor
• Interface Type: Serial (2-Wire)
• Package Type: MSOP
• Operating Temperature (min): -40C
• Operating Temperature (max): 125C
• Operating Temperature Classification: Automotive
• Operating Supply Voltage (min): 3V
• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (max): 3.6V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

If it is not, the thermal inertia caused by the sensor’s mass
causes a lag in the response of the sensor to a temperature
change. In the case of the remote sensor, this should not be
a problem since it is either a substrate transistor in the
processor or a small package device, such as the SOT−23,
placed in close proximity to it.
processor and only monitors the general ambient
temperature around the package. How accurately the
temperature of the board and/or the forced airflow reflects
the temperature to be measured dictates the accuracy of the
measurement. Self−heating due to the power dissipated in
the ADT7461A 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. In the case
of the ADT7461A, 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, q
the 8−lead MSOP is approximately 142°C/W.
Layout Considerations
the ADT7461A is measuring very small voltages from the
remote sensor, so care must be taken to minimize noise
induced at the sensor inputs. Take the following precautions:
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GND
GND
D+
D–
The on−chip sensor, however, is often remote from the
Digital boards can be electrically noisy environments, and
Place the ADT7461A as close as possible to the remote
sensing diode. Provided that the worst noise sources,
that is, 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 pickup, a 5 mil track width
and spacing is recommended. Provide a ground plane
under the tracks, if possible.
Figure 22. Typical Arrangement of Signal Tracks
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current sources, excessive cable or filter capacitance can
affect the measurement. When using long cables, the filter
capacitance can be reduced or removed.
Application Circuit
ADT7461A, using a discrete sensor transistor connected via
a shielded, twisted pair cable. The pullups on SCLK,
SDATA, and ALERT are required only if they are not
provided elsewhere in the system.
be interfaced directly to the SMBus of an I/O controller, such
as the Intel
Because the measurement technique uses switched
Figure 23 shows a typical application circuit for the
The SCLK pin and the SDATA pin of the ADT7461A can
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 mF bypass capacitor close to the V
extremely noisy environments, place an input filter
capacitor across D+ and D− close to the ADT7461A.
This capacitance can effect the temperature
measurement, so ensure that any capacitance seen at D+
and D− is, at maximum, 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. A
total of 6 feet to 12 feet is needed.
For really 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 ADT7461A. Leave the
remote end of the shield unconnected to avoid ground
loops.
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