ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 52

• Manufacturer Part Number: ADT7467
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ADT7467
The following examples illustrate circumstances that might
cause T
Normal Operation—No T
1.
2.
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.
Operating Point Exceeded—T
When the measured temperature is below the operating point
temperature minus the hysteresis, T
Once the temperature exceeds the operating temperature minus
the hysteresis (OP − Hyst), T
cycle (see Figure 70) at a rate determined by the programmed
value of n. This rate also depends on the amount that the
temperature has increased between this monitoring cycle and
Figure 72. Temperature Between Operating Point and Low Temperature Limit
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
POINT
MIN
T1(n)
OP1
MIN
POINT
MIN
LIMIT
LIMIT
T
value is not adjusted and the fan runs at a speed
MIN
is not adjusted, that is, it remains at its current setting.
to increase, decrease, or stay the same.
IS T1(n) < LOW TEMP LIMIT
ACTUAL
T
TEMP
HYSTERESIS
MIN
< HIGH TEMP LIMIT
IS T1(n) > OP1
MONITORING
Figure 71. Long Cycle Steps
T1(n) > T
T
MIN
WAIT 2n
CYCLES
AND
AND
AND
< OP1
MIN
NO
NO
MIN
MIN
MIN
and T
MIN
Adjustment
decreases during the short
YES
MIN
is not adjusted.
RANGE
MIN
Reduced
YES
remains the same.
values, defined in the
DECREASE T
T
INCREASE
MIN
CHANGE
DO NOT
BY 1°C
BY 1°C
MIN
Rev. A | Page 52 of 80
the last monitoring cycle. For example, if the temperature has
increased by 1°C, then T
has the effect of increasing the fan speed, thus providing more
cooling to the system.
If the temperature slowly increases only in the range
(OP − Hyst), that is, the change in temperature is ≤0.25°C per
short monitoring cycle, T
small changes in temperature in the desired operating zone
without changing T
in the temperature range (OP − Hyst), because the temperature
has not exceeded the operating temperature.
Once the temperature exceeds the operating temperature, T
reduces by 1°C per long cycle as long as the temperature
remains above the operating temperature. This takes place in
addition to the decrease in T
cycle. In Figure 73, because the temperature is increasing at a
rate of ≤0.25°C per short cycle, no reduction in T
during the short cycle.
Once the temperature falls below the operating temperature,
T
increase slowly, because the temperature only increases at a rate
of ≤0.25°C per cycle.
Increasing the T
When the temperature drops below the low temperature limit,
T
effect of running the fan more slowly and, therefore, more
quietly. The long cycle diagram in Figure 71 shows the
conditions necessary for T
T
1.
2.
3.
4.
MIN
MIN
MIN
The measured temperature falls below the low temperature
limit. This means that the user must choose the low limit
carefully. It should not be so low that the temperature never
falls below it, because T
fans would run faster than necessary.
T
allowed to exceed the high temperature limit. As a result,
the high limit should be chosen carefully because it deter-
mines the high limit of T
T
never be allowed to increase above the operating point
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
remains fixed, even when the temperature starts to
can increase during the long cycle. Increasing T
can increase if
MIN
MIN
is below the high temperature limit. T
is below the operating point temperature. T
MIN
MIN
Cycle
. The long cycle makes no change to T
MIN
MIN
MIN
MIN
is reduced by 2°C. Decreasing T
MIN
.
MIN
does not decrease. This allows
MIN
to increase.
would never increase and the
that occurs during the short
MIN
.
. The dynamic T
MIN
MIN
is never
MIN
MIN
takes place
MIN
control
has the
should
MIN
MIN
MIN