RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
7. Set the LUT_LOCK bit to enable the Look Up Table and begin fan control in the Fan LUT
Configuration Register.
5.4.2
DTS Support
The EMC2103 supports DTS (Intel’s Digital Temperature Sensor) data in the Fan Control Look Up
Table. Intel’s DTS data is a positive number that represents the processor’s relative temperature below
a fixed value called TCONTROL which is generally equal to 100°C for Intel Mobile processors. For
example, a DTS value of 10°C means that the actual processor temperature is 10°C below TCONTROL
or equal to 90°C.
Either or both of the Pushed Temperature Registers can be written with DTS data and used to control
the fan driver. When DTS data is entered, then the USE_DTS_Fx bit must be set in the Fan LUT
Configuration register. Once this bit is set, the DTS data entered is automatically subtracted from a
value of 100°C. This delta value is then used in the Look Up Table as standard temperature data.
APPLICATION NOTE: The device is designed with the assumption that TCONTROL is 100°C. As such, all DTS
related conversions are done based on this value including Look Up Table comparisons. If
TCONTROL is adjusted (i.e. TCONTROL is shifted to 105°C), then all of the Look Up Table
thresholds should be adjusted by a value equal to TCONTROL - 100°C.
5.5
RPM based Fan Speed Control Algorithm (FSC)
The EMC2103 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. Figure 5.4 shows a simple flow diagram of the RPM based Fan Speed Control
Algorithm operation.
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 either manually setting the TACH Target Register 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. See Section 6.30 for RPM -> TACH calculations or Appendix B for
a complied table showing this information (for default conditions).
The EMC2103’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
EMC2103 works with fans that operate up to 16,000 RPMs and provides a valid tachometer signal.
SMSC EMC2103
Revision 0.85 (01-29-08)
DATA2S7HEET
SMSC [ SMSC CORPORATION ]
