EMC2103 Datasheet, PDF (33/85 Pages) SMSC Corporation – RPM-Based Fan Controller with HW Thermal Shutdown

5.8
Ramp Rate Control
RPM-Based Fan Controller with Hardware Thermal Shutdown
Datasheet
The PWM output drive can be configured with automatic ramp rate control. If the RPM based Fan
Speed Control Algorithm is used, then this ramp rate control is automatically used based on the fan
control derivative option settings. See Section 6.23, "Fan Configuration 2 Register". The user programs
a maximum step size for the PWM setting and an update time. The update time varies from 100ms to
1.6s while the PWM maximum step can vary from 1 PWM count to 31 PWM counts.
When a new PWM is entered, the delta from the next PWM and the previous PWM is determined. If
this delta is greater than the Max Step settings, then the PWM is incrementally adjusted every 100ms
to 1.6s as determined by the Update Time until the target PWM setting is reached. See Figure 5.6.
5.9
Figure 5.6 Ramp Rate Control
Watchdog Timer
The EMC2103 contains an internal Watchdog Timer. Once the device has powered up the watchdog
timer monitors the bus 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
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.
DS0005250A-page 33
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