ADT7473 Analog Devices, Inc., ADT7473 Datasheet - Page 51

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

Figure 66 shows the steps taken during the l
The following examples illustrate some of the circumstances
that might cause T
Example 1: Normal Operation—No T
•
•
Because neither the operating point minus the hysteresis
temperature nor the low temperature limit has been exceeded,
the T
determined by the fixed T
automatic fan speed control mode.
Example 2: Operating Point Exceeded—T
When the measured temp
temperature minus the hys
MEASUREMENT
TEMPERATURE
TEMPERATURE
THERM LIMIT
OPERATING
OPERATING
HIGH TEMP
LOW TEMP
CURRENT
If measured temperature never exceeds the programmed
operating point minus the hysteresis temperature, then
T
If measured temperature never drops below the low
temperature limit, then T
MIN
POINT
T1(n)
OP1
MIN
POINT
LIMIT
LIMIT
value is not adjusted, and the fan runs at a speed
T
is not adjusted, that is, it remains
MIN
Figure 67. Temperature Between Operating Point
IS T1(n) < LOW TEMP LIM
ACTUAL
T
TEMP
HYSTERESIS
MIN
MIN
< HIGH TEMP LIMIT
IS T1(n) > OP1
Figure 66. Long Cycle Steps
and Low Temperature Limit
MONITORING
T1(n) > T
T
to increase, decrease, or stay the same.
WAIT 2n
CYCLES
MIN
AND
AND
AND
< OP1
erature is below the operating point
MIN
NO
NO
teresis, T
MIN
and T
MIN
YES
is not adjusted.
IT
RANGE
MIN
YES
MIN
remains the same.
values defined in the
Adjustment
at its current setting.
MIN
ong cycle.
DECREASE T
T
INCREASE
MIN
CHANGE
DO NOT
Reduced
BY 1°C
BY 1°C
MIN
Rev. A | Page 51 of 76
Once the temperature exceeds the operating t
the hysteresis (OP − Hyst), T
during the short cycle (see Figure 65). The rate at which T
decreases depends on the programmed value of n. It also
depends on how much the temperature has increased betwe
this monitoring cycle and the last monitoring cycle, that is, if
the temperature has increased by 1°C, then T
2°C. Decreasing T
thus providing more cooling to the system.
If the temperature slowly increases only in the rang
(OP − Hyst), that is, 0.25°C per short monit
T
temperature in the desired operating zone without changing
T
ture range (OP − Hyst) because the temperature has not
exceeded the operating temperature.
Once the temperature exceeds the operating temperature, the
long cycle causes T
while the temperature remains above the operating tempera-
ture. This takes place in addition to the decrease in T
occurs due to the short cycle. In Figure 68, because the
temperature is increasing at a rate ≤ 0.25°C per short cycle, no
reduction in T
Once the temperature falls below the operating temperature,
T
increase slowly, T
increases at a rate ≤ 0.25°C per cycle.
Example 3: Increase T
When the temperature drops below the low temperature limit,
T
effect of running the fan slower and, therefore, quieter. The long
cycle diagram in Figure 66 shows the conditions that need to be
true for T
and the reasons they need to be true follows.
T
•
•
•
•
MIN
MIN
MIN
MIN
MIN
. The long cycle makes no change to T
does not decrease. This allows small cha
stays the same. Even when the temperature starts to
can increase in the long cycle. Increasing T
can increase if
The measured temperature falls below the low temperature
limit. This means the user must choose the low limit
carefully. It should not be so low that the temperature
never falls below it because T
the fans would run faster than necessary.
T
allowed to increase above the high temperature limit. As a
result, the high limit should be sensibly chosen because it
determines how high T
T
never be allowed to increase above t
temperature because the fans would not switch on until the
temperature rose above the operating point.
The temperature is above T
is turned off below T
MIN
MIN
MIN
is below the high temperature limit. T
is below the operating point temperature. T
to increase. A quick summary of those conditions
MIN
MIN
takes place during the short c
MIN
MIN
≤
stays the same because the temperature
has the effect of increasing the fan spee
to be reduced by 1°C every long cycle
MIN
MIN
Cycle
MIN
.
MIN
can go.
starts to decrease. This occur
MIN
MIN
. The dynamic T
would never increase, and
he operating point
MIN
MIN
oring cycle, then
nges in
emperature minus
in the tempera-
ycle.
MIN
MIN
is reduced by
ADT7473
e
has the
is never
MIN
MIN
MIN
control
that
sh
MIN
ould
en
d,
s