ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 55

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

instantaneous change in temperature. This can be tested by
putting the ADT7467 into manual mode and changing the
PWM output from 0% to 100% PWM duty cycle. The PWM
output takes 35 sec to reach 100% when a ramp rate of 1 time
slot is selected.
Figure 76 shows remote temperature plotted against PWM duty
cycle for enhanced acoustics mode. The ramp rate is set to 48,
which corresponds to the fastest ramp rate. Assume that a new
temperature reading is available every 115 ms. With these
settings, it takes approximately 0.76 sec to go from 33% duty
cycle to 100% duty cycle (full speed). Even though the
temperature increases very rapidly, the fan ramps up to full
speed gradually.
Figure 77 shows how a ramp rate of 8 affects the control loop.
The overall response of the fan is slower than it is with a ramp
rate of 48. Because the ramp rate is reduced, it takes longer for
the fan to achieve full running speed. In this case, it takes
approximately 4.4 sec for the fan to reach full speed.
120
100
140
120
100
80
60
40
20
80
60
40
20
0
0
Figure 76. Enhanced Acoustics Mode with Ramp Rate = 48
0
Figure 77. Enhanced Acoustics Mode with Ramp Rate = 8
0
R
R
TEMP
TEMP
(°C)
(°C)
PWM CYCLE (%)
TIME (s)
TIME (s)
PWM DUTY CYCLE (%)
4.4
0.76
120
100
80
60
40
20
0
140
120
100
80
60
40
20
0
Rev. A| Page 55 of 80
Figure 78 shows the PWM output response for a ramp rate of 2.
With these conditions, the fan takes about 17.6 sec to reach full
running speed.
Figure 79 shows how the control loop reacts to temperature
with the slowest ramp rate. The ramp rate is set to 1; all other
control parameters are the same as they are for Figure 76
through Figure 78. With the slowest ramp rate selected, it takes
35 sec for the fan to reach full speed.
As Figure 76 to Figure 79 show, the rate at which the fan reacts
to a temperature change is dependent on the ramp rate selected
in the enhanced acoustics registers. The higher the ramp rate,
the faster the fan reaches the newly calculated fan speed.
140
120
100
120
100
80
60
40
20
80
60
40
20
0
0
0
Figure 78. Enhanced Acoustics Mode with Ramp Rate = 2
0
Figure 79. Enhanced Acoustics Mode with Ramp Rate = 1
R
TEMP
R
TEMP
(°C)
(°C)
TIME (s)
TIME (s)
PWM DUTY CYCLE (%)
PWM DUTY CYCLE (%)
17.6
35
ADT7467
140
120
100
80
60
40
20
0
120
100
80
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40
20
0