emc2105 Standard Microsystems Corp., emc2105 Datasheet - Page 29

• Manufacturer Part Number: emc2105
• Description: Emc2105 Rpm-based High Side Fan Controller With Hardware Thermal Shutdown
• Manufacturer: Standard Microsystems Corp.

RPM-Based High Side Fan Controller with Hardware Thermal Shutdown
Datasheet
APPLICATION NOTE: The device is designed with the assumption that T
SMSC EMC2105
5.4.2
5.5
5. Set the Hysteresis value to be smaller than the smallest threshold step.
6. Configure the RPM based Fan Speed Control Algorithm if it is to be used.
7. Set the LUT_LOCK bit to enable the Look Up Table and begin fan control.
DTS Support
The EMC2105 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 T
example, a DTS value of 10°C means that the actual processor temperature is 10°C below T
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. See
Appendix B
The EMC2105 includes an RPM based Fan Speed Control Algorithm. The algorithm can be controlled
manually (by setting the target fan speed) or via a look up table.
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.
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 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 EMC2105’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
EMC2105 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.
RPM based Fan Speed Control Algorithm (FSC)
the format should be in temperature with a maximum threshold of 100°C (64h). If a measurement
channel is not used, then set the threshold at FFh.
related conversions are done based on this value including Look Up Table comparisons. If
T
thresholds should be adjusted by a value equal to T
CONTROL
for examples on using DTS data in the Look Up Table.
Figure 5.4
is adjusted (i.e. T
CONTROL
shows a simple flow diagram of the RPM based Fan Speed Control
which is generally equal to 100°C for Intel Mobile processors. For
DATASHEET
CONTROL
29
is shifted to 105°C), then all of the Look Up Table
CONTROL
CONTROL
- 100°C.
is 100°C. As such, all DTS
Revision 1.74 (05-08-08)
CONTROL