Analog Devices dBCool ADT7473 Manual page 56

Remote thermal monitor and fan controller
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ADT7473
Figure 74 shows remote temper
c
ycle for enhanced acoustics m
which corresponds to the fastest ra
temperat e read g is available
ur
in
it takes approximately 0.76 seconds to go from 33% duty cycle to
100%
duty
cyc
le (f
ull speed). Ev
increa
ses ve rapidl
ry
y, the fan ra
140
( ° C)
R
TEMP
120
100
80
60
PWM CYCLE (
40
20
0
0
TIME (s)
Fig
ure 74. nhanced Acoustic
E
Figur
e 75 s
hows ow changing t
h
affects the contro
l loop. The o
slower
. Be
cause
th
e ramp ra
te is redu d, it ta
fan t
o achiev ull
e f
running speed.
appr
oxima
tely 4
.4
seconds for the fan to
120
°C)
R
(
TEMP
100
80
60
40
20
0
0
TIME (s)
Fig
ure 75 nhanced Acoust
. E
ature plotted against PWM duty
ode. The ramp rate is set to 48,
mp rate. Assume that a new
every
115 m
s. W
ith th
ese
settings
en tho h the te
ug
mp
eratur
e
mps up o full sp
t
eed
gradually.
120
100
80
60
%)
40
20
0
0.76
s Mo
de
with Ra
mp
Rate = 4
8
he ramp rate f m 48 t
ro
o 8
verall response of the fan is
ce
kes lo
nger for the
In this case, takes
it
reach full speed
.
140
120
100
80
PWM DUTY CYCLE (%)
60
40
20
0
4.4
ics M
ode wi
th Ra
mp Rate 8
=
Figure 76 shows the PWM output response for a ramp rate of 2.
In this instance, the fan took about 17.6 seconds to reach full
running speed.
,
140
R
(°C)
TE
MP
120
10
0
80
60
40
20
0
0
Figur
e 76
Fi
gur
e 77 sh
ows
wi
th
the slow t ramp
es
ot r contro arameters remain he same. W
he
l p
ra p rate se
m
lec
sp d.
ee
12
0
R
TEMP
10
0
80
60
40
20
0
0
Figure 77. Enhanced Acoustics Mode with Ramp Rate = 1
As Figure 74 to Figure 77 show, the rate at which the fan reacts
to mperatu change
te
re
th
e enha
nce
d aco
faster the fan reaches the newly calculated fan speed.
Rev. A | Page 56 of 76
P
WM
DUTY CYCLE
TIME (s)
. Enhanced Acousti
cs M
ode with Ram
how t
he c
ontro
l lo
op reacts to temperature
rat
e. The
ram
p rate is s
t
ted, it takes 35 se nds for the
co
(°C)
PWM DUTY CYCLE
TIME (s)
is
dependent on the ra
ustic
s regist
ers
. The
higher t
120
100
80
60
(%)
40
20
0
17.6
p Ra
te = 2
et to 1
, wh e all
il
ith th
e slo est
w
fan t
o reach full
140
120
100
80
60
(%)
40
20
0
35
mp ra
te se cted in
le
he ram
p r
ate, t
he

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