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參數資料
| 型號： | ADT7461AR-REEL |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 模擬信號調理 |
| 英文描述： | 【1∑C Temperature Monitor with Series Resistance Cancellation |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, PDSO8 |
| 封裝： | MS-012-AA, SOIC-8 |
| 文件頁數： | 17/24頁 |
| 文件大小： | 854K |
| 代理商： | ADT7461AR-REEL |
ADT7461
the ADT7461. A simple voltage comparator trips if the voltage
at D+ exceeds V
DD
1 V (typical), signifying an open circuit
between D+ and D. The output of this comparator is checked
when a conversion is initiated. Bit 2 of the status register (OPEN
flag) is set if a fault is detected. If the ALERT pin is enabled,
setting this flag will cause ALERT to assert low.
If the user does not wish to use an external sensor with the
ADT7461, then in order to prevent the OPEN flag being set
continuously, the user should tie the D+ and D inputs of the
ADT7461 together.
Most temperature sensing diodes have an operating temperature
range of 55°C to +150°C. Above 150°C, they lose their semicon-
ductor characteristics and approximate conductors instead. This
results in a diode short, setting the OPEN flag. The external diode
in this case will no longer give an accurate temperature meas-
urement. A read of the temperature result register will give the
last good temperature measurement. The user should be aware
that, while the diode fault is triggered, the temperature measure-
ment on the external channel may not be accurate.
THE ADT7461 INTERRUPT SYSTEM
The ADT7461 has two interrupt outputs, ALERT and THERM.
Both have different functions and behavior. ALERT is maskable
and responds to violations of software-programmed tempera-
ture limits or an open-circuit fault on the external diode.
THERM is intended as a fail-safe interrupt output that cannot
be masked.
If the external or local temperature exceeds the programmed
high temperature limits, or equals or exceeds the low tempera-
ture limits, the ALERT output is asserted low. An open-circuit
fault on the external diode also causes ALERT to assert. ALERT
is reset when serviced by a master reading its device address,
provided the error condition has gone away, and the status
register has been reset.
The THERM output asserts low if the external or local tempera-
ture exceeds the programmed THERM limits. The THERM
temperature limits should normally be equal to or greater than
the high temperature limits. THERM is reset automatically
when the temperature falls back within the THERM limit. The
external THERM limit is set by default to 85°C, as is the local
THERM limit. A hysteresis value can be programmed, in which
case, THERM will reset 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 a 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
Binary Representation
0°C
0 000 0000
1°C
0 000 0001
10°C
0 000 1010
Figure 19
shows how the THERM and ALERT outputs operate.
A user may wish to use the ALERT output as a 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 that there is a fail-safe mechanism to cool
the system, without the need for host intervention.
Figure 19. Operation of the ALERT and THERM Interrupts
Figure 19
0
1
3
2
4
THERM LIMIT
HIGH TEMP LIMIT
THERM LIMIT-HYSTERESIS
RESET BY MASTER
ALERT
THERM
100
°
C
TEMPERATURE
90
°
C
80
°
C
70
°
C
60
°
C
50
°
C
40
°
C
1.
If the measured temperature exceeds the high temperature
limit, the ALERT output will assert low.
2.
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.
3.
The THERM output deasserts (goes high) when the
temperature falls to THERM limit minus hysteresis. In
, the default hysteresis value of 10°C is shown.
4.
The ALERT output deasserts only when the temperature
has fallen below the high temperature limit, and the master
has read the device address and cleared the status register.
Pin 6 on the ADT7461 can be configured as either an ALERT
output or as an additional THERM output. THERM2 will assert
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.
Rev. 0 | Page 17 of 24
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