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参数资料
| 型号： | NCT1008DMT3R2G |
| 厂商： | ON SEMICONDUCTOR |
| 元件分类： | 模拟信号调理 |
| 英文描述： | %2B-1℃ temperature monitor with series resistance cancellation |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, DSO8 |
| 封装： | 2 X 2 MM, 0.50 MM PITCH, LEAD FREE, DFN-8 |
| 文件页数： | 7/20页 |
| 文件大小： | 251K |
| 代理商： | NCT1008DMT3R2G |
NCT1008
http://onsemi.com
15
(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 causes ALERT to assert low.
If the user does not wish to use an external sensor with the
NCT1008, tie the D+ and D inputs together to prevent
continuous setting of the open flag.
The NCT1008 Interrupt System
The NCT1008 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 opencircuit fault on
the external diode. THERM is intended as a failsafe
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 opencircuit 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 poweron
hysteresis default value is 10
°C, 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 user’s 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 9. 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. 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 failsafe mechanism to
cool the system, without the need for host intervention.
Figure 19. Operation of the ALERT and THERM
Interrupts
1
3
2
4
HIGH TEMP LIMIT
RESET BY MASTER
ALERT
THERM
1005C
TEMPERATURE
905C
805C
705C
605C
505C
405C
THERM LIMIT
THERM LIMITHYSTERESIS
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. In ,
the default hysteresis value of 10
°C is shown.
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 NCT1008 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 is
not maskable.
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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