ADT7462ACPZ-REEL ON Semiconductor, ADT7462ACPZ-REEL Datasheet - Page 21

• Manufacturer Part Number: ADT7462ACPZ-REEL
• Description: IC TEMP/VOLT MONITOR 32-LFCSP
• Manufacturer: ON Semiconductor

Specifications of ADT7462ACPZ-REEL

• Function: Fan Control, Temp Monitor
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 32-LFCSP
• Number Of Voltages Monitored: 1
• Monitored Voltage: 0.9 V to 12 V
• Manual Reset: Not Resettable
• Watchdog: No Watchdog
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 3 V
• Supply Current (typ): 4000 uA
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Layout Considerations
The ADT7462 measures 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:
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Digital boards can be electrically noisy environments.
GND
GND
Place the ADT7462 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 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. If possible, provide a
ground plane under the tracks.
Minimize the number of copper/solder joints that can
cause thermo−couple 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
because 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 large 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, an input filter capacitor
can be placed across D+ and D− close to the ADT7462.
This capacitance can affect the temperature
measurement, so care must be taken to ensure that any
capacitance seen at D+ and D− is a maximum of
1000 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 from about 6 feet up to 12 feet.
Figure 34. Typical Arrangement of Signal Tracks
D+
D–
CC
pin. In
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Noise Filtering
the industry−standard practice is to place a capacitor across
the D+ and D− pins to help combat the effects of noise.
However, large capacitances affect the accuracy of the
temperature measurement, leading to a recommended
maximum capacitor value of 1000 pF. While this capacitor
does reduce noise, it does not eliminate it, making it difficult
to use the sensor in a very noisy environment.
in eliminating the effects of noise on the external sensor. The
series resistance cancellation feature allows a filter to be
constructed between the external temperature sensor and the
device. The effect of any filter resistance seen in series with
the remote sensor is automatically canceled from the
temperature result.
remote temperature sensor to operate in noisy environments.
Figure 35 shows a low−pass RCR filter, with the following
values:
differential noise.
Voltage Measurement
voltage inputs at one time. Table 11 is a list of the voltage
measurement inputs and the corresponding input pins. Each
pin can be configured to measure the desired voltage option
using the Pin Configuration 1 (0x10) to Pin Configuration 4
(0x13) registers or the easy configuration options.
For temperature sensors operating in noisy environments,
The ADT7462 has a major advantage over other devices
The construction of a filter allows the ADT7462 and the
This filtering reduces both common−mode noise and
The ADT7462 is capable of measuring up to 13 different
For really long distances (up to 100 feet), use shielded
twisted pair, such as Belden No. 8451 microphone
cable. Connect the twisted pair to D+ and D− and the
shield to GND close to the ADT7462. Leave the remote
end of the shield unconnected to avoid ground loops.
Because the measurement technique uses switched
current sources, excessive cable or filter capacitance
can affect the measurement. When using long cables,
the filter capacitance can be reduced or removed.
Figure 35. Filter Between Remote Sensor and
R = 100 W
C = 1 nF
REMOTE
SENSOR
ADT7462
100Ω
100Ω
1nF
D+
D–