Dual RPM-Based PWM Fan Controller
Datasheet
Table 4.1 Fan Controls Active for Operating Mode
DIRECT SETTING MODE FSC MODE
Fan Driver Setting (read only)
Fan Driver Setting (read / write)
EDGES[1:0]
EDGES[1:0]
(Fan Configuration)
-
RANGE[1:0]
(Fan Configuration)
UPDATE[2:0]
(Fan Configuration)
UPDATE[2:0]
(Fan Configuration)
LEVEL
(Spin Up Configuration)
LEVEL
(Spin Up Configuration)
SPINUP_TIME[1:0]
(Spin Up Configuration)
SPINUP_TIME[1:0]
(Spin Up Configuration)
Fan Step
Fan Step
-
Fan Minimum Drive
Valid TACH Count
Valid TACH Count
-
TACH Target (read / write)
TACH Reading
TACH Reading
-
DRIVE_FAIL_CNT[1:0] and Drive Band Fail Registers
4.2
PWM Fan Driver
The EMC2302 supports 2 PWM output drivers. Each output driver can be configured to operate as an
open-drain (default) or push-pull driver and each driver can be configured with normal or inverse
polarity. Additionally, the PWM frequencies are independently programmable with ranges from 9.5Hz
to 26kHz in four programmable frequency bands.
4.3
RPM-based Fan Speed Control Algorithm (FSC)
The EMC2302 includes 2 RPM-based Fan Speed Control Algorithms. Each algorithm operates
independently and controls a separate fan driver. Each algorithm is controlled manually (by setting the
target fan speed).
This fan control algorithm uses Proportional, Integral, and Derivative terms to automatically approach
and maintain the system’s desired fan speed to an accuracy directly proportional to the accuracy of
the clock source.
The desired tachometer count is set by the user inputting the desired number of 32.768kHz cycles that
occur per fan revolution. This is done by manually setting the TACH Target Register. 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 3000 RPMs, then the user would input the
hexidecimal equivalent of 1296 (51h 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.
SMSC EMC2302
Revision 1.1 (10-12-09)
DATA1S7HEET
SMSC [ SMSC CORPORATION ]
