W83791G Nuvoton Technology Corporation of America, W83791G Datasheet - Page 29

• Manufacturer Part Number: W83791G
• Description: IC MONITOR H/W 48-LQFP
• Manufacturer: Nuvoton Technology Corporation of America

Specifications of W83791G

• Function: Hardware Monitor
• Topology: ADC
• Sensor Type: External
• Sensing Temperature: External Sensor
• Output Type: I²C™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

6.7.3
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.
Smart Fan Control
PWM
Duty
Cycle
58`C
55`C
52`C
PWM
Duty
Cycle
100
58`C
55`C
52`C
50
0
Fan Start = 20%
100
50
0
A
Fan Start = 20%
A
B
Fan Stop = 10%
Figure 10-1
Figure 10-2
- 23 -
C
B
D
C
Fan Start = 20%
Publication Release Date: April 14, 2006
D
W83791D/G
Revision 1.1