ADT7473
120
140
Slower Ramp Rates
100
80
60
40
20
R TEMP ( ? C)
PWM DUTY CYCLE (%)
120
100
80
60
40
20
The ADT7473/ADT7473 ? 1 can be programmed for
much longer ramp times by slowing the ramp rates. Each
ramp rate can be slowed by a factor of 4.
PWM1 Configuration Register (0x5C)
Bit <3> SLOW, 1 slows the ramp rate for PWM1 by 4.
PWM2 Configuration Register (0x5D)
Bit <3> SLOW, 1 slows the ramp rate for PWM2 by 4.
PWM3 Configuration Register (0x5E)
0
0
TIME (s)
35
0
Bit <3> SLOW, 1 slows the ramp rate for PWM3 by 4.
The following sections list the ramp-up times when the
Figure 80. Enhanced Acoustics Mode with
Ramp Rate = 1
As Figure 77 to Figure 80 show, the rate at which the fan
reacts to temperature change is dependent on the ramp rate
selected in the enhanced acoustics registers. The higher the
ramp rate, the faster the fan reaches the newly calculated fan
speed.
SLOW bit is set for each PWM output.
Enhanced Acoustics Register 1 (0x62)
Bits <2:0> ACOU, select the ramp rate for PWM1.
000 = 140 sec
001 = 70.4 sec
010 = 47.2 sec
011 = 28 sec
90
90
100 = 17.6 sec
80
70
60
50
40
30
20
10
PWM DUTY CYCLE (%)
R TEMP ( ? C)
80
70
60
50
40
30
20
10
101 = 12 sec
110 = 6.4 sec
111 = 3.2 sec
Enhanced Acoustics Register 2 (0x63)
Bits <2:0> ACOU3, select the ramp rate for PWM3.
000 = 140 sec
001 = 70.4 sec
010 = 47.2 sec
011 = 28 sec
100 = 17.6 sec
0 0
TIME (s)
Figure 81. How Fan Reacts to Temperature Variations
in Enhanced Acoustics Mode
Figure 81 shows the behavior of the PWM output as
temperature varies. As the temperature increases, the fan
speed ramps up. Small drops in temperature do not affect the
ramp-up function because the newly calculated fan speed is
still higher than the previous PWM value. Enhanced
acoustics mode allows the PWM output to be made less
sensitive to temperature variations. This is dependent on the
ramp rate selected and programmed into the enhanced
101 = 12 sec
110 = 6.4 sec
111 = 3.2 sec
Bits <6:4> ACOU2, select the ramp rate for PWM2.
000 = 140 sec
001 = 70.4 sec
010 = 47.2 sec
011 = 28 sec
100 = 17.6 sec
101 = 12 sec
110 = 6.4 sec
111 = 3.2 sec
acoustics registers.
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