ADT7473 Analog Devices, Inc., ADT7473 Datasheet - Page 52

• Manufacturer Part Number: ADT7473
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ADT7473
Figure 69 shows how T
ture is above T
T
operating point. Once the temperature rises above the low
temperature limit, T
Example 4: Preventing T
Because T
to reach full scale (127°C) because the fan would never swit
on. As a result, T
range:
•
•
•
OPERATING
HIGH TEMP
LOW TEMP
MIN
THERM
is below the high temperature limit and below the
POINT
The lowest possible value for T
complement mode) or −64°C (Offset 64 mode).
T
If the temperature is below T
runs at minimum speed and dynamic T
disabled.
LIMIT
LIMIT
LIMIT
T
MIN
MIN
cannot exceed the high temperature limit.
MIN
HYSTERESIS
Figure 69. Increasing T
is dynamically adjusted, i
ACTUAL
MIN
TEMP
MIN
and below the low temperature limit, and
MIN
is allowed to vary only within a specifie
MIN
stays the same.
MIN
increases when the current tempera-
from Reaching Full Scale
OPERATING
MIN
HIGH TEMP
LOW TEMP
for Quieter Operation
MIN
THERM
POINT
LIMIT
LIMIT
LIMIT
MIN
T
, the fan is switched off o
Figure 68. Effect of Exceeding O
MIN
t is undesirable for T
is −127°C (twos
HYSTERESIS
DECREASE HERE DUE TO
T1(n) – T1 (n – 1) = 0.5°C
EVERY SHORT CYCLE
MIN
SHORT CYCLE ONLY
DECREASES BY 1°C
OR 0.75°C = > T
control is
ACTUAL
TEMP
MIN
ch
MIN
d
Rev. A | Page 52 of 76
r
perating Point Minus Hysteresis Temperature
DECREASE HERE DUE TO
T1(n) – T1 (n – 1) ≤ 0.25°C
AND T1(n) > OP = > T
EVERY LONG CYCLE
DECREASES BY 1°C
LONG CYCLE ONLY
OPERATING
STEP 11: MONITORING THERM
Using the operating point limit ensures that the dynamic T
control mode operates in the best possible acoustic position
while ensuring that the temperature never exceeds the maxi-
mum operating temperature. Using the operating point limit
allows T
of its self-corrective nature. In PC design, the operating point
for the chassis is usually the worst-case internal chassis
temperature.
The optimal operating point for the processor is determined by
monitoring the thermal monitor in the Intel Pentium 4 proces-
sor. To do this, the PROCHOT output of the Pentium 4 is
connected to the THERM input of the ADT7473.
The operating point for the processor can be determined by
allowing the current temperature to be copied to the operating
point register when the PROCHOT output pulls the THERM
input low on the ADT7473. This gives the maximum
temperature at which the Pentium 4 can run before clock
modulation occurs.
HIGH TEMP
LOW TEMP
THERM
Figure 70. T
POINT
LIMIT
LIMIT
LIMIT
T
MIN
DUE TO ANY CYCLE BECAUSE
MIN
MIN
NO CHANGE IN T
T1(n) – T1 (n – 1) ≤ 0.25°C
AND T1(n) < OP = > T
to be independent of system-level issues because
HY
STAYS THE SAME
MIN
ACTUAL
STERESIS
TEMP
Adjustments Limited by the High Temperature Limit
MIN
HERE
MIN
T
FROM INCREASING
MIN
PREVENTED
MIN