EMC2103 Datasheet, PDF (30/84 Pages) SMSC Corporation – RPM-Based Fan Controller with HW Thermal Shutdown

5.7
Spin Up Routine
RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
The EMC2103 also contains programmable circuitry to control the spin up behavior of the fan driver
to ensure proper fan operation. The Spin Up Routine is initiated under the following conditions when
the Tach Period Measurement method of tach measurement is used. This applies to either the RPM
based Fan Speed Control Algorithm mode or the Direct Setting mode (with or without the Look Up
Table).
1. The TACH Target Register value changes from a value of FFh to a value that is less than the Valid
TACH Count (see Section 8.10 and Section 8.12).
2. The RPM based Fan Speed Control Algorithm’s measured TACH Reading Register value is greater
than the Valid TACH Count setting.
When the Spin Up Routine is operating, the fan driver is set to full scale (optional) for one quarter of
the total user defined spin up time. For the remaining spin up time, the fan driver output is set a a user
defined level (30% through 65% drive).
After the Spin Up Routine has finished, the EMC2103 measures the TACH signal. If the measured
TACH Reading Register value is higher than the Valid TACH Count Register setting, the FAN_SPIN
status bit is set and the Spin Up Routine will automatically attempt to restart the fan.
Figure 5.5 shows an example of the Spin Up Routine in response to a programmed fan speed change
based on the first condition above.
100%
(optional)
30% through 65%
New Target Count
Prev Target
Count = FFh
¼ of Spin Up Time
Fan Step
Algorithm controlled drive
Spin Up Time
Update Time
Target Count
Changed
Check TACH
Target Count
Reached
Figure 5.5 Spin Up Routine
Revision 0.85 (01-29-08)
30
DATASHEET
SMSC EMC2103