RPM-Based PWM Fan Controller
Datasheet
Table 4.1 Fan Controls Active for Operating Mode (continued)
DIRECT SETTING MODE FSC MODE
-
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 EMC2301 supports a PWM output driver. The output driver can be configured to operate as an
open-drain (default) or push-pull driver and the driver can be configured with normal or inverse polarity.
Additionally, the PWM frequencies is programmable with ranges from 9.5Hz to 26kHz in four
programmable frequency bands.
4.3
RPM-based Fan Speed Control Algorithm (FSC)
The EMC2301 includes an RPM-based Fan Speed Control Algorithm. The 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.
The EMC2301’s RPM-based Fan Speed Control Algorithm has programmable configuration settings
for parameters such as ramp-rate control and spin up conditions. The fan driver automatically detects
and attempts to alleviate a stalled/stuck fan condition while also asserting the ALERT# pin. The
EMC2301 works with fans that operate up to 16,000 RPMs and provide a valid tachometer signal.
The fan controller will function either with an externally supplied 32.768kHz clock source or with it’s
own internal 32kHz oscillator depending on the required accuracy. The EMC2301 offers a clock output
that enables additional devices to be slaved to the same clock source.
SMSC EMC2301
Revision 1.1 (10-12-09)
DATA1S7HEET
SMSC [ SMSC CORPORATION ]
