Step 11: Monitoring Therm - Analog Devices dBCool ADT7473 Manual

ADT7473
Figure 69 shows how T increases when the current tempera-
MIN
ture is above T and below the low temperature limit, and
MIN
T is below the high temperature limit and below the
MIN
operating point. Once the temperature rises above the low
temperature limit, T stays the same.
MIN
THERM
LIMIT
HIGH TEMP
LIMIT
OPERATING
POINT
HYSTERESIS
ACTUAL
TEMP
LOW TEMP
LIMIT
T
MIN
Figure 69. Increasing T
Example 4: Preventing T
MIN
Because T is dynamically adjusted, i
MIN
to reach full scale (127°C) because the fan would never swit
on. As a result, T is allowed to vary only within a specifie
MIN
range:
•
The lowest possible value for T
complement mode) or −64°C (Offset 64 mode).
•
T cannot exceed the high temperature limit.
MIN
•
If the temperature is below T
runs at minimum speed and dynamic T
disabled.
THERM
LIMIT
HIGH TEMP
LIMIT
OPERATING
POINT
HYSTERESIS
ACTUAL
TEMP
T
MIN
LOW TEMP
LIMIT
DECREASE HERE DUE TO
SHORT CYCLE ONLY
T1(n) – T1 (n – 1) = 0.5°C
OR 0.75°C = > T
DECREASES BY 1°C
EVERY SHORT CYCLE
Figure 68. Effect of Exceeding O
for Quieter Operation
MIN
from Reaching Full Scale
t is undesirable for T
is −127°C (twos
MIN
, the fan is switched off o
MIN
control is
MIN
NO CHANGE IN T
DUE TO ANY CYCLE BECAUSE
T1(n) – T1 (n – 1) ≤ 0.25°C
AND T1(n) < OP = > T
DECREASE HERE DUE TO
LONG CYCLE ONLY
T1(n) – T1 (n – 1) ≤ 0.25°C
AND T1(n) > OP = > T
MIN MIN
DECREASES BY 1°C
EVERY LONG CYCLE
perating Point Minus Hysteresis Temperature
THERM
LIMIT
OPERATING
POINT
LOW TEMP
LIMIT
HIGH TEMP
LIMIT
T
MIN
Figure 70. T

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 to be independent of system-level issues because
MIN
of its self-corrective nature. In PC design, the operating point
MIN
for the chassis is usually the worst-case internal chassis
ch
temperature.
d
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
r
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.
Rev. A | Page 52 of 76
HERE
MIN
MIN
STAYS THE SAME
HY STERESIS
ACTUAL
TEMP
T
MIN
FROM INCREASING
Adjustments Limited by the High Temperature Limit
MIN
PREVENTED
MIN