ASC7611 ETC2 [List of Unclassifed Manufacturers], ASC7611 Datasheet - Page 22

• Manufacturer Part Number: ASC7611
• Description: HARDWARE MONITOR WITH INTEGRATED FAN CONTROL
• Manufacturer: ETC2 [List of Unclassifed Manufacturers]

Automatic Fan Speed Control using Maximum PWM Setting
The previously described and illustrated mode had no restriction on the maximum PWM setting. It is useful to limit the
maximum PWM command sent to the fan in order to minimize the acoustic impact. The Maximum PWM setting will clamp
the automatic fan PWM command at a user selected value. The Absolute Limit setting will still cause the PWM command to
be 100% and that will remain until the temperature falls below the Absolute Limit temperature by an amount equal to the
hysteresis setting. This will minimize the acoustic impact of having a temperature moving back and forth close to the
Absolute Limit.
The Absolute Limit may be set above or below the Fan Temp Limit plus Range. The PWM value will be overridden and will
follow the hysteresis curve in either case, but the acoustic impact will be different, running the fan to 100% PWM at a lower
temperature, but enhancing the cooling effect. Absolute Limit set on the low end is shown in Figure 6. Setting it above is
shown in Figure 8.
It is important to consider the combination of Fan Temp Limit, Range, Maximum PWM and Absolute Limit and their impact
on cooling and acoustics. In addition, the capability to operate a fan from a combination of thermal zones allows a compound
linear slope to be achieved for further optimization.
© Andigilog, Inc. 2006
Maximum
Maximum
PWM %
PWM %
Speed
Speed
Fan
Fan
Figure 7 Fan Control with Absolute Limit Set below Fan Temp Limit Plus Range
Temperature
Temperature
(0 °C to 15 °C)
(0 °C to 15 °C)
Fan Temp Limit
Fan Temp Limit
PWM set to Off
PWM set to Off
less Hysteresis
less Hysteresis
Hysteresis
Hysteresis
Fan Set to Off
Fan Set to Off
Fan Set to
Fan Set to
Minimum
Minimum
Fan Temp
Fan Temp
www.andigilog.com
Limit
Limit
(2 °C to 80 °C)
(2 °C to 80 °C)
- 22 -
Range
Range
Linear Control Range
Linear Control Range
Absolute
Absolute
Limit
Limit
Fan Temp Limit
Fan Temp Limit
plus Range
plus Range
October 2006 - 70A05007
(0 °C to 15 °C)
(0 °C to 15 °C)
Hysteresis
Hysteresis
PWM 100%
PWM 100%
aSC7611