RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
5.3.1
Programming the RPM based Fan Control Algorithm
The RPM based Fan Control Algorithm powers-up enabled and active. The following registers control
the algorithm. The EMC2102 fan control registers are preloaded with defaults that will work for a wide
variety of fans so only the TACH Target Register is required to set a fan speed. The other fan control
registers can be used to fine-tune the algorithm behavior based on application requirements.
1. Set the Valid TACH Count Register to the minimum TACH count that indicates the fan is spinning.
2. Set the Spin Up Configuration Register to the spin up level and Spin Time desired.
3. Set the Fan Step Register to the desired step size.
4. Set the Fan Minimum Drive Register to the minimum drive value that will maintain fan operation.
5. Set the Update Time, and Edges options in the Fan Configuration Register.
6. Set the TACH Target Register to the desired TACH count.
5.3.2
TACH Measurement
In both modes of operation, the TACH measurement will work normally. Any TACH count that is higher
than the Valid TACH Count (see Section 6.17) will flag a stalled fan and trigger an interrupt.
The EMC2102 includes a TACH measurement circuit. The TACH signal must be valid at all times to
ensure proper operation. The TACH measurement circuitry is programmable to detect the fan speed
of a variety of fan configurations and architectures including 1-pole, 2-pole (default), 3-pole, and 4-pole
fans.
APPLICATION NOTE: The TACH measurement works independently of the drive settings. If the device is put into
manual mode and the fan drive is set at a level that is lower than the fan can operate
(including zero drive), then the TACH measurement may signal a Stalled Fan condition and
assert an interrupt.
5.3.2.1
Stalled Fan
If the TACH counter exceeds the user-programmable Valid TACH Count setting then it will flag the fan
as stalled and trigger an interrupt. If the RPM based Fan Control Algorithm is enabled, the algorithm
will automatically attempt to restart the fan until it detects a valid TACH level or is disabled.
The FAN_STALL Status bit indicates that a stalled fan was detected. This bit is checked conditionally
depending on the mode of operation.
Whenever the Manual Mode is enabled, the FAN_STALL interrupt will be masked for the duration
of the programmed Spin Up Time (see Table 6.21) to allow the fan opportunity to reach a valid
speed without generating unnecessary interrupts.
In Manual Mode, whenever the drive value is changed from 00h, the FAN_STALL interrupt will be
masked for the duration of the programmed Spin Up Time to allow the fan opportunity to reach a
valid speed without generating unnecessary interrupts.
In Manual Mode, whenever the TACH count exceeds the Valid TACH Count Register setting, the
FAN_STALL status bit will be set.
When the RPM based Fan Control Algorithm, the stalled fan condition is checked whenever the
Update Time is met and the fan drive setting is updated. It is not a continuous check.
5.3.3
Spin Up Routine
The EMC2102 also contains programmable circuitry to control the spin up behavior of the fan driver
to ensure proper fan operation. During Manual Mode, the Spin Up Routine will not control the fan drive
settings under any conditions.
SMSC EMC2102
Revision 1.95 (10-19-06)
DATA2S3HEET
SMSC [ SMSC CORPORATION ]
