EMC2302 Standard Microsystems Corp., EMC2302 Datasheet - Page 21

• Manufacturer Part Number: EMC2302
• Description: Rpm-based Pwm Fan Controller
• Manufacturer: Standard Microsystems Corp.

Dual RPM-Based PWM Fan Controller
Datasheet
APPLICATION NOTE: When the Watchdog timer is activated, the Fan Speed Control Algorithm is automatically
SMSC EMC2302
4.8
4.8.1
The EMC2302 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
Writing any other configuration registers will not disable the Watchdog Timer upon power up.
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
Update
DATASHEET
Time
Step
Max
21
Update
Time
Step
Max
Revision 1.2 (03-22-10)