ADT7476 Analog Devices, Inc., ADT7476 Datasheet - Page 47

• Manufacturer Part Number: ADT7476
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

Table 17. Selecting a T
Bits [7:4]
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
1
Actual Changes in PWM Output (Advanced Acoustics
Settings)
While the automatic fan control algorithm describes the general
response of the PWM output, it is also necessary to note that
the enhanced acoustics registers (0x62 and 0x63) can be used to
set/clamp the maximum rate of change of PWM output for a
given temperature zone. This means that if T
med with an AFC slope that is quite steep, a relatively small
change in temperature can cause a large change in PWM output
and possibly an audible change in fan speed, which can be
noticeable/annoying to users.
Decreasing the speed of the PWM output changes, by program-
ming the smoothing on the appropriate temperature channels
(Register 0x62 and Register 0x63), changes how fast the fan
speed increases/decreases in the event of a temperature spike.
The PWM duty cycle increases until the PWM duty cycle
reaches the appropriate duty cycle as defined by the AFC curve.
Figure 61 shows PWM duty cycle vs. temperature for each
T
setting affects fan speed vs. temperature. As can be seen from
the graph, the effect on fan speed is nonlinear.
Register 0x5F configures Remote 1 T
T
RANGE
RANGE
; Register 0x61 configures Remote 2 T
setting. The lower graph (B) shows how each T
1
RANGE
Value
RANGE
T
2
2.5
3.33
4
5
6.67
8
10
13.33
16
20
26.67
32 (default)
40
53.33
80
RANGE
; Register 0x60 configures local
RANGE
(°C)
.
RANGE
is program-
RANGE
Rev. B | Page 47 of 72
The graphs in Figure 61 assume that the fan starts from 0%
PWM duty cycle. Clearly, the minimum PWM duty cycle,
PWM
performs in the system. Figure 62 shows how T
when the PWM
fan actually runs at about 45% fan speed when the temperature
exceeds T
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
Figure 61. T
, needs to be factored in to see how the loop actually
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
(B)
(A)
60
60
80
80
MIN
MIN
100
100
RANGE
ADT7476
120
120
is affected
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