emc2305 Standard Microsystems Corp., emc2305 Datasheet - Page 24

• Manufacturer Part Number: emc2305
• Description: Multiple Rpm-based Pwm Fan Controller For Five Fans
• Manufacturer: Standard Microsystems Corp.

APPLICATION NOTE: When the Watchdog timer is activated, the Fan Speed Control Algorithm is automatically
Revision 1.2 (03-22-10)
4.8
4.8.1
The EMC2305 contains an internal Watchdog Timer for all fan drivers. The Watchdog timer monitors
the SMBus traffic for signs of activity and works in two different modes based upon device operation.
These modes are Power Up Operation and Continuous Operation as described below.
For either mode of operation, if four (4) seconds elapse without activity detected by the host, then the
watchdog will be triggered and the following will occur:
1. The WATCH status bit will be set.
2. The fan driver will be set to full scale drive. It will remain at full scale drive until it is disabled.
Power Up Operation
The Watchdog Timer only starts immediately after power-up. Once it has been triggered or deactivated,
it will not restart although it can be configured to operate in Continuous operation. While the Watchdog
timer is active, the device will not check for a Stalled Fan condition.
In the Power Up Operation, the Watchdog Timer is disabled by any of the following actions:
1. Writing the Fan Setting Register will disable the Watchdog Timer.
2. Enabling the RPM-based Fan Speed Control Algorithm by setting the EN_ALGO bit will disable the
Watchdog Timer
Next Desired
Previous
Watchdog Timer. The fan driver will be set based on the RPM-based Fan Speed Control Algorithm.
Setting
Setting
disabled. Disabling the Watchdog will not automatically set the fan drive nor re-activate the
Fan Speed Control Algorithm. This must be done manually.
Setting Changed
Figure 4.3 Ramp Rate Control
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Multiple RPM-Based PWM Fan Controller for Five Fans
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SMSC EMC2305
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