W83L786NR Datasheet, PDF (21/50 Pages) Winbond – H/W Monitoring IC

W83L786NR/ W83L786NG
speed. (For more cost and effort efficient solution please refer to W83391TS/QS – the DC fan pre-
driver that could provide up to 24V gate voltage for external N-channel MOSFET driving)
7.6.3 SMART FANTM I Control
W83L786NR/NG supports two sets SMART FAN^TM I function and mapping to D+,D- (PWM/DC_OUT1),
VTIN1 (PWM/DC_OUT2) . If CR80 [3:2] or CR80 [5:4] set to 2’b10, Fan1 or Fan2 will enable SMART
FAN^TM I function.
At this mode, W83L786NR/NG provides the SMART FAN^TM 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 11-1, 11-2 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 11-1
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