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Selecting T
RANGE
The T
RANGE
channel: Remote 1, Local, and Remote 2 temperature.
Bits [7:4] (T
RANGE
define the T
RANGE
Table 47. SELECTING A T
Bits [7:4] (Note 1)
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
1. Register 0x5F configures Remote 1 T
configures Local T
T
.
RANGE
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
is programmed with an AFC slope that is quite
RANGE
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.
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.
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value can be selected for each temperature
) of Register 0x5F to Register 0x61
value for each temperature channel.
VALUE
RANGE
T
RANGE
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
RANGE
; Register 0x61 configures Remote 2
RANGE
ADT7476A
Figure 61 shows PWM duty cycle vs. temperature for
each T
RANGE
T
setting affects fan speed vs. temperature. As can be
RANGE
seen from the graph, the effect on fan speed is nonlinear.
100
90
(5C)
80
70
60
50
40
30
20
10
0
0
100
90
80
70
60
50
40
30
20
10
0
0
Figure 61. T
The graphs in Figure 61 assume that the fan starts from
0% PWM duty cycle. Clearly, the minimum PWM duty
cycle, PWM
actually performs in the system. Figure 62 shows how
T
is affected when the PWM
RANGE
It can be seen that the fan actually runs at about 45% fan
speed when the temperature exceeds T
www.onsemi.com
43
setting. The lower graph shows how each
20
40
60
80
TEMPERATURE ABOVE T
20
40
60
80
TEMPERATURE ABOVE T
vs. Actual Fan Speed
RANGE
(Not PWM Drive) Profile
, needs to be factored in to see how the loop
MIN
value is set to 20%.
MIN
MIN
25C
2.55C
3.335C
45C
55C
6.675C
85C
105C
13.35C
165C
205C
26.65C
325C
405C
53.35C
805C
100
120
MIN
25C
2.55C
3.335C
45C
55C
6.675C
85C
105C
13.35C
165C
205C
26.65C
325C
405C
53.35C
805C
100
120
MIN
.
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