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Figure 78 shows the behavior of the PWM output as tempera-
ture 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 acoustics registers.
90
80
70
60
50
40
30
20
10
0
Figure 78. How Fan Reacts to Temperature Variation
in Enhanced Acoustics Mode
Slower Ramp Rates
The ADT7473 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 (Reg. 0x5C)
<3> SLOW, 1 slows the ramp rate for PWM1 by 4.
PWM2 Configuration Register (Reg. 0x5D)
<3> SLOW, 1 slows the ramp rate for PWM2 by 4.
PWM3 Configuration Register (Reg. 0x5E)
<3> SLOW, 1 slows the ramp rate for PWM3 by 4.
PWM DUTY CYCLE (%)
R
(°C)
TEMP
The following sections list the ramp-up times when the SLOW
bit is set for each PWM output.
Enhanced Acoustics Register 1 (Reg. 0x62)
<2:0> ACOU, selects the ramp rate for PWM1.
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
Enhance Acoustics Register 2 (Reg. 0x63)
<2:0> ACOU3, selects the ramp rate for PWM3.
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
<6:4> ACOU2, selects 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
Rev. 0 | Page 55 of 76
ADT7473
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