參數資料
型號： FMS2704T1C
廠商： FAIRCHILD SEMICONDUCTOR CORP
元件分類： 模擬信號調理
英文描述： SPECIALTY ANALOG CIRCUIT, PDSO24
封裝： TSSOP-24
文件頁數： 12/39頁
文件大?。?/td> 173K
代理商： FMS2704T1C
PRODUCT SPECIFICATION
FMS2704/FMS2704L
2
REV. 1.01 12/2/99
Architectural Overview
As a sensor, the FMS2704 has three monitoring functions:
1.
Tachometer
2.
Thermometer
3.
Voltmeter.
Additional functions are:
1.
Fan speed controller mode.
2.
Programmable dual fan speed outputs.
3.
Reset Generator.
Overall operation of the FMS2704 is controlled by the Serial
Bus, which sets register values and interrupt masking. Ten of
sixteen inputs can be monitored:
1.
Two remote thermal diode voltages.
2.
Local thermal diode voltage.
3.
VCC voltage.
4.
Six tachometer, TACH.
5.
V4-1 voltages instead of external diode inputs.
6.
V6-5 voltages instead of TACHA3 and TACHB3.
Following comparisons against either preset or programmable
thresholds the following hardware outputs are set:
1.
Reset, RST if VCC is low.
2.
THERM if a remote or local thermometer trip point
violated.
3.
Interrupt (INT), if:
a) Fan speed is low.
b) Remote/Local High/Low temperature limit is violated.
c) Remote diode fault.
d) V6-1 voltage out of tolerance.
Register bits also indicate status:
1.
Fan speed error.
2.
Remote high/low temperature limit violated.
3.
Local high/low temperature limit violated.
4.
THERM input asserted.
5.
Remote diode fault.
6.
Voltage error.
Tachometers
Six tachometers monitor fan speed. Stored in each 8-bit
tachometer register is the fan speed value expressed in 22.5kHz
clock counts per blade revolution. Sensitivity is established by
the Tachometer Divisor Register which matches pulse count-
ing to the sensor pulses per revolution.
Each tachometer output is compared against a low speed
threshold. A violation will trip the interrupt output to notify
System Management software or BIOS that a fault has
occurred.
Thermometers
There are three thermometers: two for remote sensing; one for
measuring local temperature. All channels utilize the thermal
variation of the voltage drop, VD across a diode, sampled at
two currents to derive the diode temperature.
To facilitate tracking of temperatures for controlling fan speed,
upper and lower temperature limits can be loaded into the
Limit Registers. If a limit is violated, the INT output is
asserted to indicate that limits must be updated and fan speed
changed. A remote diode open or short circuit fault will also
assert INT. All interrupt sources are maskable.
Maximum allowable remote and local temperatures are loaded
into the Trip Point registers. If a Trip Point is violated, the
THERM output is asserted warning that system temperature is
too high.
Instead of sensing the change in VD at one current, which is
approximately –2mV/°C, VD is sampled at two currents (IHI =
100 and ILO = 10A) to cancel out common error voltages.
Difference voltage between the two currents is proportional to
absolute temperature:
where:
n = PN junction ideality factor, typically 1.0065 for the
Pentium II thermal diode.
k = Boltmann’s constant, 1.381 x 10-23 J.K-1
T = Absolute temperature, °K
q = Electron charge, 1.602 x 10-19 C
V
D
nkT
q
----------
1n
I
HI
I
LO
--------
=
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