EMC2104 datasheet(34/101 Pages) SMSC

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Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown

Datasheet

Revision 1.74 (05-08-08)

SMSC EMC2104

DATASHEET

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.

Figure 5.6 Ramp Rate Control

Setting

Next Desired

Setting

Max

Step

Max

Step

Update

Time

Update

Time

Setting Changed

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