ADT7475 Analog Devices, Inc., ADT7475 Datasheet - Page 43

• Manufacturer Part Number: ADT7475
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

The graphs in Figure 57 assume that the fan starts from 0%
PWM duty cycle. Clearly, the minimum PWM duty cycle,
PWM
performs in the system. Figure 58 shows how T
when the PWM
fan actually 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 zones. In this
example, the following T
100
100
T
T
T
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
0
0
RANGE
RANGE
RANGE
0
0
MIN
Figure 57. T
, needs to be factored in to see how the loop actually
= 80°C for ambient temperature
= 53.33°C for CPU temperature
= 40°C for VRM temperature
MIN
20
20
.
MIN
RANGE
TEMPERATURE ABOVE T
TEMPERATURE ABOVE T
value is set to 20%. It can be seen that the
40
40
vs. Actual Fan Speed (not PWM Drive) Profile
RANGE
RANGE
(B)
(A)
60
60
values apply:
for Each Temperature
80
80
MIN
MIN
100
100
RANGE
MIN
120
120
is affected
and 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
RANGE
Rev. B | Page 43 of 68
This example uses the mux configuration described in Step 2:
Configuring the Mux, with the ADT7475 connected as shown
in Figure 48. Both CPU temperature and VRM temperature
drive the CPU fan connected to PWM1. Ambient temperature
drives the front chassis fan and rear chassis fan connected to
PWM2 and PWM3. The front chassis fan is configured to run
at PWM
PWM
PWM
Note that the control range for 4-wire fans is much wider than
that for 3-wire fans. In many cases, 4-wire fans can start with a
PWM drive of as little as 20% or less. In extreme cases, some
3-wire fans do not run unless a PWM drive of 60% or more is
applied.
100
100
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
0
0
0
0
MIN
MIN
Figure 58. T
MIN
= 30%. The CPU fan is configured to run at
= 10%.
= 20%. The rear chassis fan is configured to run at
20
20
RANGE
TEMPERATURE ABOVE T
TEMPERATURE ABOVE T
40
40
and % Fan Speed Slopes with PWM
(A)
(B)
60
60
80
80
MIN
MIN
100
100
MIN
ADT7475
120
120
= 20%
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