Fan Control Device with Hardware Monitoring and Acoustic Noise Reduction Features
Datasheet
Auto Fan Mode
Initiated
End Polling
Cycle
No
End Fan Spin
Up
Begin Polling
Cycle
Yes
Spin Up
Time Elapsed?
(5C-5E)
Fan Spinning
Up?
Yes
Set fan output to
auto fan mode
minimum speed.
(63~65)
Set Fan Output to
0%
No
Override all PWM
Temp >=
outputs to 100%
duty cycle except
if disabled or in
manual mode
Yes
AbsLimit
(69~6B)
No
No
Yes
Temp >=
Temp >= Limit
(66~68)
Off/Min set to 1?
(62)
No
No
Hyst Temp
No
(6C~6D)
Set Fan Output to
100%
Yes
Yes
Yes
Fan Output
At 0%?
Set fan to min
PWM
Begin Fan Spin-
Up
Fan Output
At 0%?
Yes
No
Set fan speed based on
Auto Fan Range
Algorithm*
Figure 6.1 Automatic Fan Control Flow Diagram
*See Registers 5C-5Eh: PWM Configuration on page 59 for details.
When in Auto Fan Control Operating Mode the hardware controls the fans directly based on monitoring
of temperature and speed.
To control the fans:
1. Set the minimum temperature that will turn the fans on. This value is programmed in Registers 67h-
69h: Zone x Low Temp Limit (Auto Fan Mode Only).
2. Set the hysteresis value for the minimum temperature that will turn the fans off. This value will hold
the fans on until the temperature goes a certain amount below the value programmed in the Zone
x Low Temp Limit registers. This value will prevent the fan from oscillating between on and off if
the temperature is around the minimum temperature limit. This value is programmed in Registers
6Dh-6Eh: Zone Hysteresis registers.
SMSC EMC6D102
Revision 0.4 (04-05-05)
DATA3S1HEET
SMSC [ SMSC CORPORATION ]
