RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
When the RPM based Fan Control Algorithm is running, the Spin Up Routine is initiated under the
following conditions:
APPLICATION NOTE: When the device is operating in manual mode, the FAN_SPIN status bit may be set if the
fan drive is set at a level that is lower than the fan can operate (including zero drive). If the
FAN_SPIN interrupt is unmasked, then this condition will trigger an errant interrupt.
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 6.18 and Section 6.17).
2. At power-up if the FAN_MODE setting is ‘1’ or ‘open’ indicating 75% drive or 60% drive
respectively. If the FAN_MODE setting is ‘0’ indicating 0% drive, then the Spin Up Routine is not
initiated until another condition is met.
3. The RPM based Fan Control Algorithm is started and the FAN_MODE setting is ‘0’ indicating 0%
drive prior to algorithm control.
4. The RPM based Fan Control Algorithm’s measured TACH count is greater than the Valid TACH
Count.
When the Spin Up Routine is operating, the fan driver is set to full scale 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 (60% or 75% drive).
After the Spin Up Routine has finished, the EMC2102 measures the TACH. If the measured TACH
count 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 5.3 shows an example of the Spin Up Routine in response to a programmed fan speed change
based on the first condition above.
100%
60% or 75%
Fan Step
New Target Count
Algorithm controlled drive
Prev Target
Count = FFh
¼ of Spin Up Time
Update Time
Spin Up Time
Target Count
Reached
Check TACH
Target Count
Changed
Figure 5.3 Spin Up Routine
Revision 1.95 (10-19-06)
SMSC EMC2102
DATA2S4HEET
SMSC [ SMSC CORPORATION ]
