W83791D Information Storage Devices, Inc, W83791D Datasheet - Page 30

• Manufacturer Part Number: W83791D
• Description: Hardware Monitor With Speech Synthesizer And Asf Functions
• Manufacturer: Information Storage Devices, Inc

6.7.3 Smart Fan Control
PWMOUT2) , temp3( FAN3, PWMOUT3) .Smart Fan Control provides two mechanisms. One is Thermal Cruise
mode and the other is Fan Speed Cruise mode.
6.7.3.1 Thermal Cruise mode
temperatures of CPU and the system within specific range. At first a wanted temperature and interval must be set (ex.
55 C
setting value. Once the temperature exceeds the high limit ( 58 C), the fan will be turned on with a specific speed set
by BIOS (ex: 80% duty cycle) and automatically controlled its PWM duty cycle with the temperature varying. Three
conditions may occur :
(1) If the temperature still exceeds the high limit (ex: 58 C), PWM duty cycle will increase slowly. If the fan has
been operating in its full speed but the temperature still exceeds the high limit (ex: 58 C), a warning message will be
issued to protect the system.
(2) If the temperature goes below the high limit (ex: 58 C), but still above the low limit (ex: 52 C), the fan speed
will be fixed at the current speed because the temperature is in the target range (ex: 52 C ~ 58 C).
(3) If the temperature goes below the low limit (ex: 52 C), PWM duty cycle will decrease slowly to 0 or a preset
stop value until the temperature exceeds the low limit.
Figure 10-1, 10-2 gives an illustration of Thermal Cruise Mode.
W83791D supports three Smart Fan function and mapping to temp1 (FAN1, PWMOUT1), temp2 (FAN2,
At this mode, W83791D provides the Smart Fan system to automatically control fan speed to keep the
3 C) by BIOS and the fan speed will be lowered as long as the current temperature remains below the
PWM
Duty
Cycle
58`C
55`C
52`C
100
50
0
PWM Clock Input
Fan Start = 20%
A
G
B
Figure 10-1.
D
S
R1
NMOS
23
Figure 9.
+12V
C
R2
D
+
-
PNP Transistor
C
Publication Release Date: Aug, 2001
FAN
W83791D
Preliminary
Revision 0.41