ADM1031ARQZ Просмотр технического описания (PDF) - ON Semiconductor
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ADM1031ARQZ Datasheet PDF : 30 Pages
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ADM1031
4. Try to minimize the number of copper/solder
joints, which can cause thermocouple effects.
Where copper/solder joints are used, make sure
that they are in both the D+ and D– path and at the
same temperature.
Thermocouple effects should not be a major problem as
1°C corresponds to about 200 mV, and thermocouple
voltages are about 3 mV/°C of temperature difference.
Unless there are two thermocouples with a big temperature
differential between them, thermocouple voltages should be
much less than 200 mV.
5. Place a 0.1 mF bypass capacitor close to the
ADM1031.
6. If the distance to the remote sensor is more than
8 inches, the use of twisted pair cable is
recommended. This works up to about 6 to 12 feet.
7. For extra long distances (up to 100 feet), use a
shielded twisted pair cable, such as the Belden #8451
microphone cable. Connect the twisted pair to D+
and D– and the shield to GND close to the
ADM1031. Leave the remote end of the shield
unconnected to avoid ground loops.
Because the measurement technique uses switched
current sources, excessive cable and/or filter capacitance
can affect the measurement. When using long cables, the
filter capacitor C1 can be reduced or removed. In any case
the total shunt capacitance should not exceed 1000 pF.
Cable resistance can also introduce errors. One ohm series
resistance introduces about 0.5°C error.
Addressing the Device
ADD (Pin 13) is a three−state input. It is sampled, on
powerup to set the lowest two bits of the serial bus address.
Up to three addresses are available to the systems designer
via this address pin. This reduces the likelihood of conflicts
with other devices attached to the system management bus.
The Interrupt System
The ADM1031 has two interrupt outputs, INT and
THERM. These have different functions. INT responds to
violations of software programmed temperature limits and
is maskable.
THERM is intended as a “fail−safe” interrupt output that
cannot be masked. If the temperature is below the low
temperature limit, the INT pin is asserted low to indicate an
out−of−limit condition. If the temperature exceeds the high
temperature limit, the INT pin is also asserted low. A third
limit, THERM limit, can be programmed into the device to
set the temperature limit above which the overtemperature
THERM pin is asserted low. The behavior of the high limit
and THERM limit is as follows:
1. Whenever the temperature measured exceeds the
high temperature limit, the INT pin is asserted low.
2. If the temperature exceeds the THERM limit, the
THERM output asserts low. This can be used to
throttle the CPU clock. If the THERM−to−Fan
Enable bit (Bit 7 of THERM behavior/revision
register) is cleared to 0, then the fans do not run
full−speed. The THERM limit can be programmed
at a lower temperature than the high temperature
limit. This allows the system to run in silent mode,
where the CPU can be throttled while the cooling
fan is off. If the temperature continues to increase,
and exceeds the high temperature limit, an INT is
generated. Software can then decide whether the
fan should run to cool the CPU. This allows the
system to run in silent mode.
3. If the THERM−to−Fan Enable bit is set to 1, then
the fan runs full−speed whenever THERM is
asserted low. In this case, both throttling and active
cooling take place. If the high temperature limit is
programmed to a lower value than the THERM
limit, exceeding the high temperature limit asserts
INT low. Software could change the speed of the
fan depending on temperature readings. If the
temperature continues to increase and exceeds the
THERM limit, THERM asserts low to throttle the
CPU and the fan runs full−speed. This allows the
system to run in performance mode, where active
cooling takes place and the CPU is only throttled
at high temperature.
Using the high temperature limit and the THERM limit in
this way allows the user to gain maximum performance from
the system by only slowing it down, should it be at a critical
temperature.
Although the ADM1031 does not have a dedicated
interrupt mask register, clearing the appropriate enable bits
in Configuration Register 2 clears the appropriate interrupts
and masks out future interrupts on that channel. Disabling
interrupt bits prevents out−of−limit conditions from
generating an interrupt or setting a bit in the status registers.
Using THERM as an Input
The THERM pin is an open−drain input/output pin. When
used as an output, it signals overtemperature conditions.
When asserted low as an output, the fan is driven full−speed
if the THERM−to−Fan Enable bit is set to 1 (Bit 7 of Register
0×3F). When THERM is pulled low as an input, the THERM
bit (Bit 7) of Status Register 2 is set to 1, and the fans are
driven full−speed. Note that the THERM−to−Fan Enable bit
has no effect whenever THERM is used as an input. If
THERM is pulled low as an input, and the THERM−to−Fan
Enable bit = 0, then the fans are still driven full−speed. The
THERM−to−Fan Enable bit only affects the behavior of
THERM when used as an output.
Status Registers
All out−of−limit conditions are flagged by status bits in
Status Register 1 (0×02) and Status Register 2 (0×03). Bit 0
(Alarm Speed) and Bit 1 (Fan Fault) of Status Register 1,
once set, can be cleared by reading Status Register 1. Once
the alarm speed bit is cleared, this bit is not reasserted on the
next monitoring cycle even if the condition still persists.
This bit can be reasserted only if the fan is no longer at alarm
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