W83L786NR Datasheet, PDF (23/50 Pages) Winbond – H/W Monitoring IC

W83L786NR/ W83L786NG
The SMART FAN^TM II, a new innovation of Winbond, is specifically designed to operate fans at the
lowest possible speed so as to minimize acoustic noise. As the figure shown above, it is clear that
SMART FAN^TM II describes a relationship between Fan PWM Duty Cycle/DC Level and temperature.
Users can program CR [80h] to enable SMART FAN^TM II mode. SMART FAN^TM II registers allow users to
define suitable fan output levels to improve acoustic noise, power consumption and reliability issues
regarding to specific fan.
Each fan has 4 duty cycle registers and 4 temperature point registers to setup the relation between fan
output and temperature. Tolerance registers CR [8Dh] is used to postpone the response of fan output
and avoid fan output throttles at each temperature point because fan throttling might produce some
undesired noise.
The mechanism of SMART FAN^TM II is described as follows:
(1) At first, the fan speed operates at Non-Stop Duty Cycle, and keeps constant while temperature
rises. When rising temperature hits critical Temp.1, fan speed remains unchanged. If the
temperature keeps on rising and finally hits the upper edge of Temp. Tolerance of Temp.1, it
triggers the fan speed change mechanism and fan speed jumps from Non-Stop Duty Cycle to Fan
Duty Cycle Level 1.
(2) Fan speed remains constant at Fan Duty Cycle Level 1 even though the monitored temperature
hits Temp.2.
(3) Fan speed will directly jump from Fan Duty Cycle Level 1 to Fan Duty Cycle Level 2 while the
monitored temperature hits the upper edge of Temp. Tolerance of Temp.2.
(4) Same mechanism happens between Temp.3 and Temp.4.
(5) If the monitored temperature between Temp.3 and Temp.4, for example, begins to fall, the fan will
keep its speed at Fan Duty Cycle Level 3, which is a constant.
(6) If the monitored temperature keeps on falling, the fan speed still remains the same unless the
temperature hits the lower edge of Temp. Tolerance of Temp.3.
(7) Once the monitored temperature hits the lower edge of Temp. Tolerance of Temp.3, the fan speed
reduces directly from Fan Duty Cycle Level 3 to Fan Duty Cycle Level 2, and keeps the same
speed until the temperature hits the next lower edge of Temp. Tolerance.
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