ADT7473 Analog Devices, Inc., ADT7473 Datasheet - Page 43

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

Increasing or decreasing PWM
although the fan control still follows the same PWM duty cycle
to temperature slope. The effective T
values can be calculated using Equation 2.
where (Max DC − Min DC) × T
value.
See the Note on Fan Speed and PWM Duty Cycle section.
Figure 56 shows PWM duty cycle vs. temperature for each
T
affects fan speed vs. temperature. As indicated by the graph, the
effect on fan speed is nonlinear.
RANGE
100
100
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
0
0
T
0
0
MAX
setting. The lower graph shows how each T
= T
20
20
MIN
Figure 56. T
+ (Max DC − Min DC) × T
TEMPERATURE ABOVE T
TEMPERATURE ABOVE T
40
40
RANGE
vs. Actual Fan Speed Profile
60
60
MIN
RANGE
changes the effective T
80
80
/170 is the effective T
RANGE
MIN
MIN
for different PWM
100
100
RANGE
/170
RANGE
120
120
setting
2°C
2.5°C
3.33°C
4°C
5°C
6.67°C
8°C
10°C
13.3°C
16°C
20°C
26.6°C
32°C
40°C
53.3°C
80°C
2°C
2.5°C
3.33°C
4°C
5°C
6.67°C
8
1
13.3°
16°C
20°C
26.6°C
32°C
40°C
53.3°C
80°C
RANGE
°C
0°C
RANGE
C
Rev. A | Page 43 of 76
MIN
(2)
,
The graphs in Figure 56 assume the fan starts from 0% PWM
duty cycle. Clearly, the minimum PWM duty cycle, PWM
needs to be factored in to see how the loop actually performs in
the system. Figure 57 shows how T
PWM
runs at about 45% fan speed when the temperature exceeds T
Example: Determining T
Channel
The following example shows how the different T
settings can be applied to three different thermal zon
example, the following T
This example uses the mux configuration described in the Step 2:
Configuring the Mux section, with the ADT7473 connected as
shown in Figure 58. Both CPU temperature and VRM temperature
drive the CPU fan connected to PWM1. Ambient temperature
drives the fro
P
at
PWM
PWM
WM2 and PWM3. The front chassis fan is configured to run
100
100
PWM
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
0
0
0
0
T
T
T
MIN
MIN
MIN
RANGE
RANGE
RANGE
Figure 57. T
MIN
= 30%. The CPU fan is configured to run at
= 10%.
value is set to 20%. It can be seen that the fan actually
= 20%. The rear chassis fan is configured torun at
= 80°C for ambient temperature
= 53.3°C for CPU temperature
= 40°C for VRM temperature
20
20
nt chassis fan and rear chassis fan connected to
RANGE
TEMPERATURE ABOVE T
TEMPERATURE ABOVE T
40
40
and % Fan Speed Slopes with PWM
RANGE
RANGE
60
60
values apply:
for Each Temperat
RANGE
80
80
MIN
MIN
is affected when the
100
100
MIN
MIN
ADT7473
120
120
= 20%
an
es. In this
ure
d T
2°C
2.5°C
3.33°C
4°C
5°C
6.67°C
8°C
10°C
13.3°C
16°C
20°C
26.6°C
32°C
40°C
53.3°C
80°C
2°C
2.5°C
3.33°C
4°C
5°C
6.67°C
8°C
10°C
13.3°C
16°C
20°C
26.6°C
32°C
40°C
53.3°C
80°C
MIN
RANGE
MIN
,
.