ADT7473 Analog Devices, Inc., ADT7473 Datasheet - Page 40

• Manufacturer Part Number: ADT7473
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ADT7473
STEP 4: PWM
PWM
the system runs. It is also the start speed for each fan under
automatic fan control once the temperature rises above T
(see Figure 50). For maximum system acoustic benefit, PWM
should be set as low a
P
This va
More tha
temperature measurement channel. For example, Remote 1
temperature can control PWM1 and PWM2 outputs. If two
different fans are used on PWM1 and PWM2, the fan
characteristics can be s
by PWM1 can have a different PWM
conn
(front fa
PWM2
However, both fans turn on at exactly the same temperatur
defined by T
WM
ected to PWM2. Figure 51 illustrates this as PWM
MIN
MIN
lue can be found through fan validation.
MIN
PWM2
PWM1
PWM
Figure 50. PWM
n) is turned on at a minimum duty cycle of 20%, while
n one PWM output can e controlled from si
is the minimum PWM duty cycle at which each fan
setting is usually in the 20% to 33% duty cycle range.
100%
100%
(rear fan) turns on at a minimum of 40% duty cycle.
MIN
0%
MIN
MIN
0%
MIN
Figure 51. Operating Two Different Fans
.
MIN
from a Single Temperature Channel
FOR EACH PWM (FAN) OUTPUT
MIN
s possible. Depending on the fan used, the
T
et up differently. As a result, Fan 1 driven
T
MIN
Determines Minimum PWM Duty Cycle
MIN
b
TEMPERATURE
MIN
TEMPERATURE
value than that of Fan 2
a ngle
1
MIN
MIN
e,
Rev. A | Page 40 of 76
MIN
in
Programming the PWM
The PWM
min
anyw
duty
The
Example 1: For a minimum PWM duty cycle of 50%
Exam
PWM
Register 0x64, PWM1
(50% default)
Register 0x
(50% d
Regist
(50% d
Note
The P
RPM.
runnin
cycle a
is beca
root o
drive s
STEP 5: PWM
PWM
system runs under the automatic fa
maximum system acoustic benefit, PWM
possible, but should be capable of maintaining the process
temperature limit at an acceptable level. If the THERM
temperature limi
for f
There is a PWM
of this register is 0
programmed.
im
ail-safe cooling (see Figure 52).
value to be programmed into the PWM
Value (decimal) = PWM
Value (decimal) = 50/0.39 = 128 (decimal)
Value = 128 (decimal) or 80 (hex)
Value (decimal) = 33/0.39 = 85 (decimal)
Value = 85 (decimal) or 54 (hex)
cycle to be set in steps of 0.39%.
%
here from 0% to 100%. This allows the minimum
ple 2: For a minimum PWM duty cy
MIN
on Fan Speed a
WM duty cycle d
er 0x66, PWM3
f PWM duty cycl
MAX
Running a fan a
use fan speed in
ignal, fan speed
um
ctually runs the fan at closer to 50% of its full speed. This
efault)
efault)
g the fan at 33%
fanspeed
Registers
is the maximum duty cycle at w
MIN
PW
65, PWM2
registers are 8-bit registers that allow the
M
MAX
MAX
=
t is exceeded, the fans are still boosted to 100%
duty cycle for each output t
xFF and thus has no effect unless it is
limit for each fan channel. The default
PW
FOR PW (FAN) OUTPUTS
t 33% P
Minimum Duty Cycle = 0x80
Minimum D
Minim
in RPM appr
e. Give
nd P
oes n
%R
speed
M
MIN
PM generally relates to the square
du
WM Duty Cycle
ot directly correlate to fan speed in
MIN
. Driving a fan at 33% PWM duty
um Duty Cycle = 0x80
ty
Registers
WM duty cycle does not equate to
n a PWM square wave as the
M
/0.39
cycle
uty Cycle = 0x80
n speed control loop. For
oximates to
×
10
MAX
hich each fan in the
MIN
cle of 33%
o be
should b
register is given by
config
e as low as
PWM
ured
or
value