RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
5.2
Fan Control Modes of Operation
The EMC2102 has two modes of operation for the High Side Fan Driver. They are:
1. Manual Mode - in this mode of operation, the user directly controls the fan drive setting. Updating
the Fan Driver Setting Register (see Section 6.12) will instantly update the fan drive.
The Manual Mode is enabled by clearing the EN bit in the Fan Configuration Register (see
Section 6.13).
Whenever the Manual Mode is enabled the current drive will be changed to what was last written
into the Fan Driver Setting Register.
Setting the drive value to 00h will disable the High Side Fan Driver for lower power operation.
2. Using RPM based Fan Control Algorithm - in this mode of operation, the user determines a target
TACH count and the drive setting is automatically updated to achieve this target speed. The
algorithm uses the Spin Up Routine and has user definable ramp rate controls.
Table 5.1 Fan Controls Active for Operating Mode
MANUAL MODE
ALGORITHM
Fan Driver Setting (read only)
Fan Driver Setting (read / write)
EDGES[1:0]
EDGES[1:0]
(Fan Configuration)
-
-
-
UPDATE[2:0]
(Fan Configuration)
LEVEL
(Spin Up Configuration)
SPINUP_TIME[1:0]
(Spin Up Configuration)
-
Fan Step
-
Fan Minimum Drive
Valid TACH Count
TACH Target
Valid TACH Count
-
TACH Reading
TACH Reading
5.3
RPM based Fan Control Algorithm
The EMC2102 includes a RPM based Fan Control Algorithm that controls an integrated linear High
Side Fan Driver. This fan control algorithm automatically approaches and maintains the system’s
desired fan speed to an accuracy directly proportional to the accuracy of the clock source. Figure 5.2
shows a simple flow diagram of the RPM based Fan Control Algorithm operation.
The desired TACH count is set by the user inputting the desired number of 32.768KHz cycles that
occur per fan revolution. The user may change the target count at any time. The user may also set
the target count to FFh in order to disable the fan driver for lower current operation.
For example, if a desired RPM rate for a 2-pole fan is 3000RPMs, then the user would input the
hexidecimal equivalent of 655 (29h in the TACH Target Register). This number represents the number
of 32.768KHz cycles that would occur during the time it takes the fan to complete a single revolution
when it is spinning at 3000RPMs (see Equation [3] in Section 6.19).
SMSC EMC2102
Revision 1.95 (10-19-06)
DATA2S1HEET
SMSC [ SMSC CORPORATION ]
