ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 40

• Manufacturer Part Number: ADT7468
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7468
PROGRAMMING THE AUTOMATIC FAN SPEED CONTROL LOOP
Note that to more efficiently understand the automatic fan
speed control loop, it is strongly recommended to use the
ADT7468 evaluation board and software while reading this
section.
This section provides the system designer with an understand-
ing of the automatic fan control loop, and provides step-by-step
guidance for effectively evaluating and selecting critical system
parameters. To optimize the system characteristics, the designer
needs to give some thought to system configuration, including
the number of fans, where they are located, and what tempera-
tures are being measured in the particular system.
The mechanical or thermal engineer who is tasked with the
system thermal characterization should also be involved at the
beginning of the process.
STEP 1: HARDWARE CONFIGURATION
During system design, the motherboard sensing and control
capabilities should be addressed early in the design stages.
Decisions about how these capabilities are used should involve
the system thermal/mechanical engineer. Ask the following
questions:
1.
What ADT7468 functionality will be used?
•
•
PWM2 or SMBALERT ?
TACH4 fan speed measurement or overtemperature
THERM function?
AMBIENT TEMP
REMOTE 1 =
REMOTE 2 =
VRM TEMP
CPU TEMP
LOCAL =
THERMAL CALIBRATION
THERMAL CALIBRATION
THERMAL CALIBRATION
T
T
T
MIN
MIN
MIN
T
T
T
RANGE
RANGE
RANGE
100%
100%
100%
0%
0%
0%
Figure 53. Hardware Configuration Example
MUX
Rev. A | Page 40 of 84
PWM
PWM
PWM
MIN
MIN
MIN
2.
3.
4.
ENHANCEMENT)
ENHANCEMENT)
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
TACHOMETER 2
MEASUREMENT
TACHOMETER 3
MEASUREMENT
•
•
The ADT7468 offers multifunctional pins that can be
reconfigured to suit different system requirements and
physical layouts. These multifunction pins are software
programmable.
How many fans will be supported in system, three or four?
This influences the choice of whether to use the TACH4
pin or to reconfigure it for the THERM function.
Is the CPU fan to be controlled using the ADT7468 or will
it run at full speed 100% of the time?
If it runs at 100%, this frees up a PWM output, but the
system is louder.
Where will the ADT7468 be physically located in the
system?
This influences the assignment of the temperature
measurement channels to particular system thermal zones.
For example, locating the ADT7468 close to the VRM
controller circuitry allows the VRM temperature to be
monitored using the local temperature channel.
(ACOUSTIC
(ACOUSTIC
(ACOUSTIC
CONTROL
CONTROL
CONTROL
RAMP
RAMP
RAMP
AND 4
5 V voltage monitoring or overtemperature THERM
function?
12 V voltage monitoring or VID5 input?
GENERATOR
GENERATOR
GENERATOR
CONFIG
CONFIG
CONFIG
PWM
PWM
PWM
PWM
PWM
PWM
PWM1
TACH1
PWM2
TACH2
PWM3
TACH3
FRONT CHASSIS
REAR CHASSIS
CPU FAN SINK