ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 46

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

ADT7467
Increasing or decreasing PWM
but the fan control still follows the same PWM duty cycle to
temperature slope. The effective T
be calculated using Equation 2:
where:
(Max DC − Min DC) × T
See the Fan Speed and PWM Duty Cycle section.
Figure 64 shows PWM duty cycle vs. temperature for each
T
affects fan speed vs. temperature. As can be seen from the
graph, the effect on fan speed is nonlinear.
The graphs in Figure 64 assume that the fan starts from 0%
PWM duty cycle. The minimum PWM duty cycle, PWM
must be factored in to determine how the loop performs in the
system. Figure 65 shows how T
PWM
about 45% fan speed when the temperature exceeds T
RANGE
100
100
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
0
0
0
T
0
MIN
MAX
setting. The lower graph shows how each T
value is set to 20%. It can be seen that the fan runs at
= T
20
20
MIN
Figure 64. T
+ (Max DC − Min DC) × T
TEMPERATURE ABOVE T
TEMPERATURE ABOVE T
40
40
RANGE
RANGE
60
60
/170 is the effective T
vs. Fan Speed Profile
MIN
RANGE
RANGE
changes the effective T
80
80
is affected when the
MIN
MIN
for a PWM
100
100
RANGE
/170
RANGE
MIN
120
120
RANGE
MIN
value can
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°C
10°C
13.3°C
16°C
20°C
26.6°C
32°C
40°C
53.3°C
80°C
value.
.
MIN
RANGE
,
Rev. A | Page 46 of 80
(2)
,
Determining T
The following example shows how different T
settings can be applied to three thermal zones. In this example,
the following T
This example uses the mux configuration described in the
Step 2: Configuring the Mux section, with the ADT7467
connected as shown in Figure 56. Both CPU temperature and
VRM temperature drive the CPU fan connected to PWM1.
Ambient temperature drives the front chassis fan and the rear
chassis fan connected to PWM2 and PWM3. The front chassis
fan is configured to run at PWM
is configured to run at PWM
configured to run at PWM
4-Wire Fans
The control range for 4-wire fans is much wider than that of
2-wire or 3-wire fans. In many cases, 4-wire fans can start with
a PWM drive of as little as 20%.
Figure 65. T
100
100
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
0
0
T
T
T
0
0
RANGE
RANGE
RANGE
RANGE
= 80°C for ambient temperature
= 53.3°C for CPU temperature
= 40°C for VRM temperature
20
20
RANGE
and Percentage of Fan Speed Slopes with PWM
RANGE
TEMPERATURE ABOVE T
TEMPERATURE ABOVE T
40
40
values apply:
for Each Temperature Channel
MIN
60
60
MIN
= 10%.
= 30%. The CPU fan is
MIN
80
80
= 20%; the rear chassis fan
MIN
MIN
100
100
MIN
and T
120
120
MIN
RANGE
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
= 20%