W83L784R_05 Datasheet, PDF (21/52 Pages) Winbond – Monitoring IC

W83L784R/ W83L784G
6.5.3 Smart Fan Control
Smart Fan Control provides two mechanisms. One is Thermal Cruise mode and the other is Fan
Speed Cruise mode.
6.5.3.1. Thermal Cruise mode
At this mode, W83L784R/G provides the Smart Fan system which can control the fan speed
automatically depend on current temperature to keep it with in a specific range. At first a wanted
temperature and interval must be set (ex. 55 °C ± 3 °C) by BIOS, as long as the current temperature
remains below the setting value, the fan will be off. Once the temperature exceeds the setting high
limit temperature (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 fully speed but the temperature still exceeds the high limit (ex: 58°C), a
warning message or a fan_fault signal(pin5) will be issued to protect the system.
(2) If the temperature goes below the high limit (ex: 58°C), but above the low limit (ex: 52°C), the fan
speed will be fixed at the current speed because the temperature is in the target area (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 value until the temperature exceeds the low limit.
Figure 17 gives an illustration for Thermal Cruise Mode.
58`C
55`C
52`C
A
B
PWM ¹⁰⁰
Duty
Cycle ⁵⁰
0
Fan Start = 20%
C
D
Figure 17-1
- 16 -
Publication Release Date: Jan. 2005
Revision 1.1