參數(shù)資料
型號: LM92CIMX
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 溫度/濕度傳感器
英文描述: 【0.33∑C Accurate, 12-Bit Sign Temperature Sensor and Thermal Window Comparator with Two-Wire Interface
中文描述: DIGITAL TEMP SENSOR-SERIAL, 13BIT(s), 1.50Cel, RECTANGULAR, SURFACE MOUNT
封裝: 0.150 INCH, PLASTIC, SOP-8
文件頁數(shù): 15/18頁
文件大?。?/td> 396K
代理商: LM92CIMX
3.0 Application Hints
The temperature response graph in Figure 7 depicts a typi-
cal application designed to meet ACPI requirements. In this
type of application, the temperature scale is given an arbi-
trary value of
granularity
, or the window within which tem-
perature notification events should occur. The LM92 can be
programmed to the window size chosen by the designer, and
will issue interrupts to the processor whenever the window
limits have been crossed. The internal flags permit quick de-
termination of whether the temperature is rising or falling.
The T_CRIT limit would typically use its separate output to
activate hardware shutdown circuitry separate from the pro-
cessor. This is done because it is expected that if tempera-
ture has gotten this high that the processor may not be re-
sponding. The separate circuitry can then shut down the
system, usually by shutting down the power supply.
Note that the INT and T_CRIT_A outputs are separate, but
can be wire-or’d together.Alternatively the T_CRIT_Acan be
diode or’d to the INT line in such a way that a T_CRIT_A
event activates the INT line, but an INT event does not acti-
vate the T_CRIT_A line. This may be useful in the event that
it is desirable to notify both the processor and separate
T_CRIT_A shutdown circuitry of a critical temperature alarm
at the same time (maybe the processor is still working and
can coordinate a graceful shutdown with the separate shut-
down circuit).
To implement ACPI compatible sensing it is necessary to
sense whenever the temperature goes outside the window,
issue an interrupt, service the interrupt, and reprogram the
window according to the desired granularity of the tempera-
ture scale. The reprogrammed window will now have the cur-
rent temperature inside it, ready to issue an interrupt when-
ever the temperature deviates from the current window.
To understand this graph, assume that at the left hand side
the system is at some nominal temperature. For the 1st
event temperature rises above the upper window limit,
T
, causing INT to go active. The system responds to the
interrupt by querying the LM92’s status bits and determines
that T
was exceeded, indicating that temperature is ris-
ing. The system then reprograms the temperature limits to a
value higher by an amount equal to the desired granularity.
Note that in Event Interrupt Mode, reprogramming the limits
has caused a second, known, interrupt to be issued since
temperature has been returned within the window. In Com-
parator Interrupt Mode, the LM92 simply stops issuing inter-
rupts.
The 2nd event is another identical rise in temperature. The
3rd event is typical of a drop in temperature. This is one of
the conditions that demonstrates the power of the LM92, as
the user receives notification that a lower limit is exceeded in
such a way that temperature is dropping.
The Critical Alarm Event activates the separate T_CRIT_A
output. Typically, this would feed circuitry separate from the
processor on the assumption that if the system reached this
temperature, the processor might not be responding.
DS101051-15
Note:
Event Interrupt mode is drawn as if the user is reading the part. If the user doesn’t read, the outputs would go low and stay that way until the LM92 is read.
FIGURE 7. Temperature Response Diagram for ACPI Implementation
L
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