ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 49

• Manufacturer Part Number: ADT7468
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• 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
See the Note on Fan Speed and PWM Duty Cycle.
Figure 65 shows PWM duty cycle versus temperature for each
T
affects fan speed versus temperature. As can be seen from the
graph, the effect on fan speed is nonlinear.
The graphs in Figure 65 assume that the fan starts from 0%
PWM duty cycle. Clearly, the minimum PWM duty cycle,
PWM
performs in the system. Figure 66 shows how T
when the PWM
fan actually runs at 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
T
0
0
MIN
MAX
setting. The lower graph shows how each T
, needs to be factored in to see how the loop actually
MIN
= T
20
20
.
MIN
Figure 65. T
MIN
+ (Max DC − Min DC) × T
TEMPERATURE ABOVE T
TEMPERATURE ABOVE T
value is set to 20%. It can be seen that the
40
40
RANGE
RANGE
vs. Actual Fan Speed Profile
60
60
/170 is the effective T
MIN
changes the effective T
80
80
RANGE
MIN
MIN
for different PWM
100
100
RANGE
RANGE
/170
RANGE
RANGE
120
120
is affected
setting
value.
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. A | Page 49 of 84
MIN
(2)
,
Example: Determining T
The following example shows how the different T
settings can be applied to three different thermal zones. In this
example, the following T
This example uses the MUX configuration described in Step 2,
with the ADT7468 connected as shown in Figure 57. 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
20%. The rear chassis fan is configured to run at PWM
30%. The CPU fan is configured to run at PWM
Note on 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%.
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
Figure 66. T
= 80°C for ambient temperature
= 53.3°C for CPU temperature
= 40°C for VRM temperature
20
20
RANGE
TEMPERATURE ABOVE T
TEMPERATURE ABOVE T
and % Fan Speed Slopes with PWM
40
40
RANGE
RANGE
60
60
values apply:
for Each Temperature Channel
80
80
MIN
MIN
100
100
MIN
MIN
MIN
ADT7468
120
120
= 10%.
= 20%
and T
MIN
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
=