ADT7473 Analog Devices, Inc., ADT7473 Datasheet - Page 33

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

PROGRAMMING THE AUTOMATIC
To understand the automatic fan speed control loop, it is
strongly recommended to use the ADT7473 evaluation board
and software while reading this section.
This section provides
ing f the automatic fan control loop, and provid
guidance on effectively evaluating and selecting cr
para
needs to consider the system configuration, including the
num
are meas
The
syste
begi
AUTOM
T
on the measured temperature. This is done independently of
CPU intervention once initial parameters are set up.
The ADT7473 has a local temperature sensor and
temperature channels that can be connected to a CPU on-chip
thermal diode (available on Intel Pentium class CPUs and other
CPUs). These three temperature channels can be used as the
basis for automatic fan speed control to drive fans using PWM.
he ADT7473 can automatically control the speed of fans based
o
nning of the process.
me rs. To optimize the system
mechanical or thermal engineer who is tasked with the
ber f fans, where they are located, and what temperatures
m thermal characterization should also be involved at th
te
o
ured in the particular
ATIC FAN
REMOTE 1
REMOTE 2
LOCAL
the system designer with an understand-
TEMP
TEMP
TEMP
CONTROL OVERVIEW
THERMAL CALIBRATION
THERMAL CALIBRATION
THERMAL CALIBRATION
system.
T
T
T
MIN
MIN
MIN
characteristics, the designer
T
T
T
RANGE
RANGE
RANGE
es step-by-step
Figure 44. Automatic Fan Control Block Diagram
itical system
two remote
100%
100%
100%
FAN SPEED CO T
0%
0%
0%
MUX
Rev. A | Page 33 of 76
e
PWM
PWM
PWM
Auto
ing an speed according to accurately measured temperature.
Re
tion. The a
to th
and
channel and, therefore, for a given fan, are critical because they
def e the thermal characteristics of the system. The therm
valid
the d
Figu
circu
to th
cont
used to control up to four fans. The ADT7473 allows the speed
of four fans to be monitored. Each temperature channel has a
thermal calibration block, allowing the designer to individually
configure the thermal characteristics of each temperature
channel. For example, a designer can decide to run the CPU fan
when CPU tem
when the local temperature increases above 45°C. At this stage,
the designer has not assigned these thermal calibration settings
to a particular fan drive (PWM) channel. The right side of
Figure 44 shows controls that are fan-specific. The designer has
individual control over parameters such as minimum PWM
duty cycle, fan speed failure thresholds, and even ramp control
of the PWM outputs. Automatic fan control, then, ultimately
allows graceful fan speed changes that are less perceptible to the
system user.
MIN
MIN
MIN
N ROL LOOP
du
in
f
T
re 44 gives a top-level overview of the automatic fan control
rol three PWM outputs. The three PWM outputs c
e number of programmable parameters, including T
ree system temperatures can be monitored and used to
matic fan speed control reduces acoustic noise by optimiz-
ation of t
esign process, so these values should be selected car
itry on the ADT7473. From a systems-level perspective
cing fan speed can also decrease system current consump-
RANGE
ENHANCEMENT)
ENHANCEMENT)
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
TACHOMETER 2
MEASUREMENT
TACHOMETER 3
MEASUREMENT
(ACOUSTIC
(ACOUSTIC
(ACOUSTIC
CONTROL
CONTROL
CONTROL
RAMP
RAMP
RAMP
AND 4
utomatic fan speed control mode is
. The T
he system is one of the most important steps in
perature increases above 60°C, and a chassis fan
MIN
and T
GENERATOR
GENERATOR
GENERATOR
CONFIG
CONFIG
CONFIG
PWM
PWM
PWM
PWM
PWM
PWM
RANGE
value
PWM1
TACH1
PWM2
TACH2
PWM3
TACH3
s for a temperature
very flexible due
ADT7473
an be
efully.
MIN
al
, up