Analog Devices dBCool ADT7473 Manual page 57

Figure 78 shows the behavior of the PWM output as tempera-
ture v aries . As th temperature in e
up. Small drops in temp erature do not affect the ramp-up
functi on b ecaus he newly calcul e t
than the previous PWM value. Enhanced acoustics mode allows
the P WM outpu o be made less t t
varia tions. This is dep endent on t
prog ramm ed in to the enhanced aco
90
80
70
60
50
40
30
20
10
0
Figure 78 . How Fa n Reacts to T
in Enhanced A
Slower Ramp Ra tes
The ADT7473 ca n be programm
by slo wing t he r am p rates. Each ram
factor of 4.
PWM1 Configu ation Register (0x5C) r
Bit [3] SLOW, 1 sl ows the ramp
PWM 2 Co nfigu ation Register ( r
Bit [3] SLOW, 1 sl o ws the ram
PWM 3 Co nfigu ation Regis r
Bit [3] SLOW, 1 sl ows the ram
cre es, the fan speed mps as ra
ate d fan s ed pe is still higher
sen ive to t sit em peratu re
he r mp rate selected and a
u tics regi s sters.
PWM DUTY CYCLE (%)
R (°C)
TEM P
empera ture Variatio n
coust ics Mo de
ed for much longer ramp times
p rate can be sl owe d by a
rate for PWM1 by 4.
0 x5D)
p rate for PWM2 by 4.
ter (0 x5E)
p rate for PWM3 by 4.
The followin g sect
bit is set for each PWM output.
Enhance Acoustics Register 1 (0x62)
Bi ts [2:0] A O C U, select the ramp te for PWM1.
000 = 140 sec
001 = 70.4 sec
010 = 47.2 sec
011 = 28 sec
100 = 17.6 s
101 = 12 sec
110 = 6.4 sec
1 11 = 3 .2 se
Enhance 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 s c
100 = 1 7.6 se
101 = 12 sec
110 = 6 .4 sec
111 = 3.2 sec
B its [6:4] AC OU2, s
000 = 140 sec
001 = 7 0.4 sec
010 = 47.2 sec
011 = 2 8 sec
100 = 17.6 sec
101 = 1 2 sec
110 = 6.4 sec
11 1 = 3 .2 sec
Rev. A | Page 57 of 76
ions list th e ra mp-u p times
ra
ec
c
e
c
ele ct the ram p rat e for PWM2.
ADT7473
when th e SLOW