Legacy Fan Speed Control
112
Thermal and Mechanical Design Guidelines
These are the minimum parameters required to implement acoustic fan speed control.
See Figure
7-40 for an example. There may be vendor specific options that offer
enhanced functionality. See the appropriate vendor datasheet on how to implement
those features.
Figure
7-40. Fan Speed Control
Diode Temperature
(°C)
T
CONTROL
Min Speed
Fa
n
S
peed
(RPM)
Full Speed
T
LOW
X %
Fa
n
S
peed
(%
P
W
M D
u
ty
Cy
cle)
100 %
Diode Temperature
(°C)
T
CONTROL
Min Speed
Fa
n
S
peed
(RPM)
Full Speed
T
LOW
X %
Fa
n
S
peed
(%
P
W
M D
u
ty
Cy
cle)
100 %
E.2.1.1
Temperature to begin fan acceleration
The first item to consider is the value for T
LOW
. The FSC device needs a minimum
temperature to set as the threshold to begin increasing PWM duty cycle to the fan.
The system designer might initially consider a small temperature range (T
CONTROL
–
T
LOW
= T
RANGE
), 5 °C to accelerate the fan. That would delay the fan accelerating for
the longest time after an increase in T
SENSOR
. There are a number of issues that should
be considered with this strategy
•
There is little granularity in the fan speeds. For each 1 °C of increase in diode
temperature = 20% jump in PWM duty cycle %
•
Fan speed oscillation as the thermal solution chases the on-die thermal sensor
temperature
•
Having T
SENSOR
overshoot T
CONTROL
and the thermal profile causing the Thermal
Control Circuit to activate to reduce the temperature.
•
In extreme cases THERMTRIP# activates and shuts down the processor
The first two cases can create a poor acoustic response for the user. The third case
the user could notice a drop in performance as the thermal control circuit reduces the
power. Figure
7-41 is an example of this situation. The system begins at idle and the
Maxpower program is started at 65% workload.
Summary of Contents for Celeron Dual-Core E1000 Series
Page 10: ...10 Thermal and Mechanical Design Guidelines...
Page 26: ...Processor Thermal Mechanical Information 26 Thermal and Mechanical Design Guidelines...
Page 68: ...ATX Thermal Mechanical Design Information 68 Thermal and Mechanical Design Guidelines...
Page 86: ...Heatsink Clip Load Metrology 86 Thermal and Mechanical Design Guidelines...
Page 88: ...Thermal Interface Management 88 Thermal and Mechanical Design Guidelines...
Page 120: ...Legacy Fan Speed Control 120 Thermal and Mechanical Design Guidelines...
Page 126: ...Fan Performance for Reference Design 126 Thermal and Mechanical Design Guidelines...
Page 127: ...Fan Performance for Reference Design Thermal and Mechanical Design Guidelines 127...
