Board And System Implementation; Choosing Fan Speed Control Settings; Figure 17. Example Acoustic Fan Speed Control Implementation - Intel EM64T - Celeron D 336 Boxed Ena User Manual

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6.3

Board and System Implementation

Once the thermal solution is defined, the system designer and board designer can define the fan
speed control implementation. The first step is to select the appropriate fan speed controller
(FSC). Figure 17 shows the major connections for a typical implementation.

Figure 17. Example Acoustic Fan Speed Control Implementation

Inlet Ambient Inlet Ambient
(Thermistor) (Thermistor)
HS Fan HS Fan
Processor Processor
A number of major manufacturers have FSC components that include the necessary functionality
to measure the temperature of the on-die thermal diode and output a PWM signal. These
components can be a discrete device or a super I/O (SIO) with the functionality embedded. The
following vendors currently have components that could be suitable: Analog Devices, ITE,
Maxim, National Semiconductor, SMSC and Winbond. Consult their web sites or local sales
representatives for a part suitable for your design. See Appendix E for further details on the
motherboard requirements
6.3.1

Choosing Fan Speed Control Settings

Fan speed control algorithms allow the system thermal engineer a number of options to consider.
The typical control settings that need to be considered are:
• The temperature when the fan will begin to accelerate in response to the on-die thermal diode
temperature (T
• The temperature where the fan speed is operating at full speed (100% PWM duty cycle). By
specification this is T
• The minimum fan speed (PWM duty cycle). For any on-die thermal diode temperature less
than T
These are the minimum parameters required to implement acoustic fan speed control. See
Figure 18 for an example. There may be vendor specific options that offer enhanced functionality.
See the appropriate vendor datasheet on how to implement those features.
Thermal/Mechanical Design Guide
4-Pin Fan 4-Pin Fan
Header Header
GND GND
Modulation (PWM) Modulation (PWM)
Thermal Diode Thermal Diode
)
LOW
CONTROL
the fan will run at this speed
LOW
Sys Sys
Ambient Ambient
(Opt) (Opt)
+12V +12V
Tachometer Tachometer
Fan Speed Fan Speed
Pulse Width Pulse Width Controller Controller
(2 wires) (2 wires)
T T
CONTROL CONTROL
Acoustic Fan Speed Control
Sys Fan Sys Fan
4wire 4wire
PWM PWM
(2x) (2x)
BIOS BIOS
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