EMC2113 datasheet(33/85 Pages) SMSC

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RPM-Based Fan Controller with Multiple Temperature Zones & Hardware Thermal Shutdown

Datasheet

SMSC EMC2113

Revision 1.2 (10-08-09)

DATASHEET

6.10

Watchdog Timer

The EMC2113 contains an internal Watchdog Timer for the fan driver. 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 which will cause the ALERT pin to be asserted.

2. The fan driver will be set to full scale drive. It will remain at full scale drive until it is disabled.

APPLICATION NOTE: When the Watchdog timer is activated the Fan Speed Control Algorithm is automatically

disabled. Disabling the Watchdog will not automatically set the fan drive nor re-activate the

Fan Speed Control Algorithm. This must be done manually.

6.10.1

Power Up Operation

The Watchdog Timer only starts immediately after power-up and once it has been triggered or

deactivated will not restart although it can be configured to operate in Continuous operation.

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. The fan driver will be set based on the RPM-based Fan Speed Control Algorithm.

3. Changing the Watchdog operating mode by setting the WD_EN bit.

Writing any other configuration registers will not disable the Watchdog Timer upon power up.

Figure 6.5 Ramp Rate Control

Setting

Next Desired

Setting

Max

Step

Max

Step

Update

Time

Update

Time

Setting Changed

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