ADT7461AR-REEL7 ON Semiconductor, ADT7461AR-REEL7 Datasheet - Page 18

• 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
the high temperature limits. THERM is reset automatically
when the temperature falls back within the THERM limit. The
external limit is set by default to 85°C, as is the local THERM
limit. A hysteresis value can be programmed so that THERM
resets when the temperature falls to the limit value minus the
hysteresis value. This applies to both local and remote
measurement channels. The power-on hysteresis default value is
10°C, but this may be reprogrammed to any value after power-
up.
The hysteresis loop on the THERM outputs is useful when
THERM is used for on/off control of a fan. The user’s system
can be set up so that when THERM asserts, a fan can be
switched on to cool the system. When THERM goes high again,
the fan can be switched off. Programming an hysteresis value
protects from fan jitter where the temperature hovers around
the THERM limit, and the fan is constantly being switched.
Table 13. THERM Hysteresis
THERM Hysteresis
0°C
1°C
10°C
Figure 21 shows how the THERM and ALERT outputs operate.
A user may choose to use the ALERT output as an SMBALERT
to signal to the host via the SMBus that the temperature has
risen. The user could use the THERM output to turn on a fan to
cool the system, if the temperature continues to increase. This
method would ensure there is a fail-safe mechanism to cool the
system without the need for host intervention.
TEMPERATURE
1.
2.
3.
THERM
ALERT
100°C
90°C
80°C
70°C
60°C
50°C
40°C
If the measured temperature exceeds the high temperature
limit, the ALERT output asserts low.
If the temperature continues to increase and exceeds the
THERM limit, the THERM output asserts low. This can be
used to throttle the CPU clock or switch on a fan.
The THERM output deasserts (goes high) when the
temperature falls to THERM limit minus hysteresis. The
Figure 21. Operation of the ALERT and THERM Interrupts
1
2
Binary Representation
0 000 0000
0 000 0001
0 000 1010
3
RESET BY MASTER
4
THERM LIMIT
THERM LIMIT-HYSTERESIS
HIGH TEMP LIMIT
Rev. 3 | Page 18 of 23 | www.onsemi.com
4.
Pin 6 on the ADT7461 can be configured as either an ALERT
output or as an additional THERM output. THERM2 asserts
low when the temperature exceeds the programmed local
and/or remote high temperature limits. It is reset in the same
manner as THERM, and it is not maskable. The programmed
hysteresis value applies to THERM2 also.
Figure 22 shows how THERM and THERM2 might operate
together to implement two methods of cooling the system. In
this example, the THERM2 limits are set lower than the
THERM limits. The THERM2 output could be used to turn on
a fan. If the temperature continues to rise and exceeds the
THERM limits, the THERM output could provide additional
cooling by throttling the CPU.
1.
2.
3.
4.
Both the external and internal temperature measurements cause
THERM and THERM2 to operate as described.
THERM2
THERM
TEMPERATURE
90°C
80°C
70°C
60°C
50°C
40°C
30°C
default hysteresis value of 10°C is shown in Figure 21.
The ALERT output deasserts only when the temperature
falls below the high temperature limit, and the master has
read the device address and cleared the status register.
When the THERM2 limit is exceeded, the THERM2 signal
asserts low.
If the temperature continues to increase and exceeds the
THERM limit, the THERM output asserts low.
The THERM output deasserts (goes high) when the
temperature falls to THERM limit minus hysteresis. No
hysteresis value is shown in Figure 22.
As the system continues to cool and the temperature falls
below the THERM2 limit, the THERM2 signal resets.
Again, no hysteresis value is shown for THERM2.
Figure 22. Operation of the THERM and THERM2 Interrupts
1
2
3
4
THERM LIMIT
THERM2 LIMIT