adt7476a Analog Devices, Inc., adt7476a Datasheet - Page 45

• Manufacturer Part Number: adt7476a
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

Selecting T
The T
Remote 1, local, and Remote 2 temperature. Bits [7:4] (T
of Register 0x5F to Register 0x61 define the T
each temperature channel.
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
enhance 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
with an AFC slope that is quite steep, a relatively small change
in temperature could cause a large change in PWM output and
possibly an audible change in fan speed, which can be noticeable/
bothersome to end users.
Register 0x5F configures Remote 1 T
T
RANGE
; Register 0x61 configures Remote 2 T
Figure 60. Changing PWM Max Does Not Change the AFC Slope
RANGE
1
100%
PWM
MAX
10%
0%
value can be selected for each temperature channel:
RANGE
T
MIN–HYST
RANGE
Value
T
RANGE
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
; Register 0x60 configures local
RANGE
RANGE
.
(°C)
RANGE
RANGE
is programmed
value for
RANGE
Rev. 0 | Page 45 of 72
)
Decreasing the speed the PWM output changes by programming
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 slowly 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
affects fan speed vs. temperature. As can be seen from the
graph, the effect on fan speed is nonlinear.
The graphs in Figure 61 assume that 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 62 shows how T
PWM
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
0
0
MIN
Figure 61. T
setting. The lower graph shows how each T
value is set to 20%. It can be seen that the fan actually
20
20
RANGE
TEMPERATURE ABOVE T
TEMPERATURE ABOVE T
40
40
vs. Actual Fan Speed (Not PWM Drive) Profile
(B)
(A)
60
60
RANGE
80
80
MIN
MIN
is affected when the
100
100
ADT7476A
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°C
10°C
13.3°C
16°C
20°C
26.6°C
32°C
40°C
53.3°C
80°C
MIN
MIN
,
.