W83792AD/AG/D/G
Must be take care when choosing the OP-AMP and the transistor. The OP-AMP is used for amplify the
5V range of the DC output up to 12V. The transistor should has a suitable β value to avoid its base
current pulling down the OP-AMP ’s output and gain the common current to operate the fan at fully
speed. (For more cost and effort efficiently solution please refer to W8339TS/QS –which is the DC fan
pre-driver and it could provide up to 24V gate voltage for external N-channel MOSFET with lower cost
and better performance)
7.7.3 Smart FanTM I Control
W83792D/G supports two 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 Smart FanTM II mode.
7.7.3.1. Thermal Cruise mode
At this mode, W83792D/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 7-1, 7-2 gives an illustration of Thermal Cruise Mode.
A
B
D
C
58`C
55`C
52`C
Fan Start = 20%
100
50
0
PWM
Duty
Cycle
Figure 7-1.
Publication Release Date: April 26, 2006
Revision 0.9
- 23 -
WINBOND [ WINBOND ]
