W83791D Datasheet, PDF (30/46 Pages) Winbond – W83791D Winbond H/W Monitoring IC

W83791D
+12V
R1
R2
PWM Clock Input
D
G
NMOS
S
PNP Transistor
+
C
FAN
-
Preliminary
Figure 9.
6.7.3 Smart Fan Control
W83791D supports three Smart Fan function and mapping to temp1 (FAN1, PWMOUT1), temp2 (FAN2,
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
At this mode, W83791D provides the Smart Fan system to automatically control fan speed to keep the
temperatures of CPU and the system within specific range. At first a wanted temperature and interval must be set (ex.
55 °C ± 3 °C) by BIOS and the fan speed will be lowered as long as the current temperature remains below the
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.
58`C
55`C
52`C
A
B
C
D
PWM ¹⁰⁰
Duty
Cycle ⁵⁰
0
Fan Start = 20%
Figure 10-1.
23
Publication Release Date: Aug, 2001
Revision 0.41