RPM-Based Fan Controller with Multiple Temperature Zones & Hardware Thermal Shutdown
Datasheet
This functionality is always active. If the pin does not transition, then it will assume 100% duty cycle
or 0% duty cycle based on the pin voltage. The data range required by the Look Up Table is 0 to 127
so 100% duty cycle corresponds to 127 and 0% corresponds to 0.
The duty cycle measured on the PWM_IN pin is compared against a user programmed PWM High
Limit. If the measured duty cycle meets or exceeds this value, then it may cause the ALERT pin to be
asserted (default operation is to mask this event from asserting the ALERT pin).
6.6
RPM-Based Fan Speed Control Algorithm (FSC)
The EMC2113 includes an RPM-based Fan Speed Control Algorithm.
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 either manually or by programming the Temperature Look-
Up Table. 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 RPM 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 EMC2113’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
EMC2113 works with fans that operate up to 16,000 RPMs and provide a valid tachometer signal.
6.6.1
Programming the RPM-Based Fan Speed Control Algorithm
The RPM-based Fan Speed Control Algorithm powers-up disabled. The following registers control the
algorithm. The EMC2113 fan control registers are pre-loaded 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.
Note that steps 1 - 7 are optional and need only be performed if the default settings do not provide
the desired fan response.
1. Set the Valid TACH Count Register to maximum number of tach counts to indicate 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 tachometer count.
7. Enable the RPM-based Fan Speed Control Algorithm by setting the EN_ALGO bit.
6.7
Tachometer Measurement
The tachometer measurement circuitry is used in conjunction with the RPM-based Fan Speed Control
Algorithm to update the fan driver output. Additionally, it can be used in Direct Setting mode as a
diagnostic for host based fan control.
Revision 1.2 (10-08-09)
SMSC EMC2113
DATA3S0HEET
SMSC [ SMSC CORPORATION ]
