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| 型号： | NCT72CMTR2G |
| 厂商： | ON Semiconductor |
| 文件页数： | 15/20页 |
| 文件大小： | 326K |
| 描述： | IC REMOTE THERMAL SENSOR 8-WDFN |
| 标准包装： | 1 |
| 功能： | 温度监控系统（传感器） |
| 传感器类型： | 内部和外部 |
| 感应温度： | 0°C ~ 127°C，-64°C ~ 191°C |
| 精确度： | ±2.5°C |
| 拓扑： | ADC，比较器，多路复用器，寄存器库 |
| 输出类型： | 2 线串行，I²C?/SMBUS? |
| 输出警报： | 是 |
| 输出风扇： | 是 |
| 电源电压： | 2.8 V ~ 3.6 V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-WFDFN |
| 供应商设备封装： | 8-WDFN（2x2） |
| 包装： | 标准包装 |
| 其它名称： | NCT72CMTR2GOSDKR |
NCT72
http://onsemi.com
15
fault is detected. If the ALERT
pin is enabled, setting this
flag causes ALERT
to assert low.
If the user does not wish to use an external sensor with the
NCT72, tie the D+ and D inputs together to prevent
continuous setting of the open flag.
The NCT72 Interrupt System
The NCT72 has two interrupt outputs, ALERT
and
THERM
. Both have different functions and behavior.
ALERT
is maskable and responds to violations of software
programmed temperature 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 temperature 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
temperature exceeds the programmed THERM
limits.
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. A hysteresis value can be programmed; in
which case, 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癈, but this can be
reprogrammed to any value after powerup.
The hysteresis loop on the THERM
outputs is useful when
THERM
is used, for example, as an on/off controller for a
fan. The users system can be set up so that when THERM
asserts, a fan is 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 switched.
Table 14. THERM
HYSTERESIS
THERM
Hysteresis
Binary Representation
0癈
0 000 0000
1癈
0 000 0001
10癈
0 000 1010
Figure 19 shows how the THERM
and ALERT
outputs
operate. The ALERT
output can be used as a SMBALERT
to signal to the host via the SMBus that the temperature has
risen. The user can use the THERM
output to turn on a fan
to cool the system, if the temperature continues to increase.
This method ensures 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
1005C
THERM
LIMIT
905C
805C
705C
605C
505C
405C
THERM
LIMIT HYSTERESIS
HIGH TEMP LIMIT
RESET BY MASTER
TEMPERATURE
1
2
3
4
ALERT
THERM
?SPAN class="pst NCT72CMNR2G_2296365_3"> If the measured temperature exceeds the high
temperature limit, the ALERT
output asserts low.
?SPAN class="pst NCT72CMNR2G_2296365_3"> 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.
?SPAN class="pst NCT72CMNR2G_2296365_3"> The THERM
output deasserts (goes high) when the
temperature falls to THERM
limit minus hysteresis. In ,
the default hysteresis value of 10癈 is shown.
?SPAN class="pst NCT72CMNR2G_2296365_3"> 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.
?SPAN class="pst NCT72CMNR2G_2296365_3"> Pin 6 on the NCT72 can be configured as either an
ALERT
output or as an additional THERM
output.
?SPAN class="pst NCT72CMNR2G_2296365_3"> 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 is
not maskable.
?SPAN class="pst NCT72CMNR2G_2296365_3"> The programmed hysteresis value also applies to
THERM2
.
Figure 20 shows how THERM
and THERM2
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 is used to turn on a
fan. If the temperature continues to rise and exceeds the
THERM
limits, the THERM
output provides additional
cooling by throttling the CPU.
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