emc2105 Standard Microsystems Corp., emc2105 Datasheet - Page 34

• Manufacturer Part Number: emc2105
• Description: Emc2105 Rpm-based High Side Fan Controller With Hardware Thermal Shutdown
• Manufacturer: Standard Microsystems Corp.

APPLICATION NOTE: Disabling the Watchdog will not automatically set the fan drive. This must be done manually
Revision 1.74 (05-08-08)
5.9
The EMC2105 contains an internal Watchdog Timer. Once the device has powered up the watchdog
timer monitors the SMBus traffic for signs of activity. The Watchdog Timer starts when the internal
supply has reached its operating point. The Watchdog Timer only starts immediately after power-up
and once it has been triggered or deactivated will not restart.
If four (4) seconds elapse without the system host programming the device, 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 one of the three
If the Watchdog Timer is triggered, the following three operations will disable the timer and return the
device to normal operation. Alternately, if the Watchdog Timer has not yet been triggered performing
any one of the following will disable it.
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
3. Setting the LUT_LOCK bitwill disable the Watchdog Timer. The fan driver will be set based on the
Writing any other configuration registers will not disable the Watchdog Timer.
Watchdog Timer
Next Desired
Previous
conditions listed below are met.
Watchdog Timer. The fan driver will be set based on the RPM based Fan Speed Control Algorithm.
Look Up Table settings.
Setting
Setting
(or via the Look Up Table).
Setting Changed
Figure 5.6 Ramp Rate Control
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RPM-Based High Side Fan Controller with Hardware Thermal Shutdown
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Max
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Time
Step
Max
SMSC EMC2105
Datasheet