W83791G Datasheet, PDF (29/99 Pages) Winbond – Winbond H/W Monitoring IC

W83791D/G
6.7.3 Smart Fan Control
W83791D/G 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/G 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.
A
B
C
D
58`C
55`C
52`C
PWM <sup>100</sup>
Duty
Cycle <sup>50</sup>
0
Fan Start = 20%
Figure 10-1
A
B
58`C
55`C
52`C
PWM ¹⁰⁰
Duty
Cycle ⁵⁰
Fan Start = 20%
0
Fan Stop = 10%
Figure 10-2
D
C
Fan Start = 20%
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Publication Release Date: April 14, 2006
Revision 1.1