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© Andigilog, Inc. 2006
www.andigilog.com
October 2006 - 70A06010
aSC7621
Figure 9 Fan Control with Absolute Limit Set above Fan Temp Limit Plus Range
Figure 10 Automatic Fan Control Algorithm
Begin Fan
Spin up
Set Fan Output
to 100%
End Polling
Cycle
Begin Polling
Cycle
Fan
Output
At 0%?
Fan
Spinning
Up?
Set fan output
to auto fan mode
minimum speed
Set Fan Output
to 0%
Temp >=
AbsLimit?
Temp >=
Limit?
Fan
Output at
0%?
Off /
Min set
to 1?
Below
Hysteresis?
Override PWM
Output to 100%
Set fan speed
based on Auto Fan
Range Algorithm
Auto Fan Mode
Initiated
Yes
Yes
(Minimum Speed)
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
(off)
Yes
Min Speed
or Spin-Up
Time Met?
End Fan
Spin Up
PWM=
100%?
Yes
No
Below
Hysteresis?
Yes
No
PWM=
<Max PWM
No
Yes
Set Fan Output
to Max PWM
Begin Fan
Spin up
Set Fan Output
to 100%
End Polling
Cycle
Begin Polling
Cycle
Fan
Output
At 0%?
Fan
Spinning
Up?
Set fan output
to auto fan mode
minimum speed
Set Fan Output
to 0%
Temp >=
AbsLimit?
Temp >=
Limit?
Fan
Output at
0%?
Off /
Min set
to 1?
Below
Hysteresis?
Override PWM
Output to 100%
Set fan speed
based on Auto Fan
Range Algorithm
Auto Fan Mode
Initiated
Yes
Yes
(Minimum Speed)
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
(off)
Yes
Min Speed
or Spin-Up
Time Met?
End Fan
Spin Up
PWM=
100%?
Yes
No
Below
Hysteresis?
Yes
No
PWM=
<Max PWM
No
Yes
Set Fan Output
to Max PWM
PWM set to Off
PWM 100%
Fan Temp Limit
less Hysteresis
Fan Temp
Limit
Hysteresis
(0
°C to 15 °C)
Range
(2
°C to 80 °C)
Fan Temp Limit
plus Range
Absolute
Limit
PW
M D
uty
Cyc
le l
ine
arly
Inc
rea
sin
g w
ith
Tem
p
PW
M D
uty
Cyc
le li
nea
rly
Dec
rea
sing
with
Tem
p
Fan Set to Off
Temperature
Fan
Speed
Linear Control Range
Fan Set to
Minimum
Hysteresis
(0
°C to 15 °C)
Maximum
PWM %
PWM set to Off
PWM 100%
Fan Temp Limit
less Hysteresis
Fan Temp
Limit
Hysteresis
(0
°C to 15 °C)
Range
(2
°C to 80 °C)
Fan Temp Limit
plus Range
Absolute
Limit
PW
M D
uty
Cyc
le l
ine
arly
Inc
rea
sin
g w
ith
Tem
p
PW
M D
uty
Cyc
le li
nea
rly
Dec
rea
sing
with
Tem
p
Fan Set to Off
Temperature
Fan
Speed
Linear Control Range
Fan Set to
Minimum
Hysteresis
(0
°C to 15 °C)
Maximum
PWM %
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