Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
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Figure 5.6 Ramp Rate Control
5.9
Watchdog Timer
The EMC2104 contains two internal Watchdog Timers. 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.
Each fan driver has an independent watchdog timer. Disabling the watchdog associated with Fan 1
will not disable the watchdog associated with Fan 2.
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
conditions listed below are met.
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
Watchdog Timer. The fan driver will be set based on the RPM based Fan Speed Control Algorithm.
3. Setting the LUT_LOCK bit will disable the Watchdog Timer. The fan driver will be set based on the
Look Up Table settings.
Writing any other configuration registers will not disable the Watchdog Timer.
Revision 1.74 (05-08-08)
SMSC EMC2104
DATA3S4HEET
SMSC [ SMSC CORPORATION ]
