Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
5.4.1
Programming the Look Up Table
When the Look Up Table is used, it must be loaded and configured correctly based on the system
requirements. The following steps outline the procedure.
1. Determine whether the Look Up Table will drive a fan setting or a tachometer target value and set
the TACH / DRIVE bit in the Fan LUT Configuration Register.
2. Determine which measurement channels (up to four) are to be used with the Look Up Table and
set the TEMP3_CFG and TEMP4_CFG bits accordingly in the Fan LUT Configuration Register.
3. For each step to be used in the LUT, set the Fan Setting (either fan setting or TACH Target as set
by the TACH / DRIVE bit). If a setting is not used, then set it to FFh (if a fan setting) or 00h (if a
TACH Target). Load the lowest settings first in ascending order (i.e. Fan Setting 1 is the lowest
setting greater than “off”. Fan Setting 2 is the next highest setting, etc.).
4. For each step to be used in the LUT, set each of the measurement channel thresholds. These
values must be set in the same data format that the data is presented. If DTS is to be used, then
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.
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.
5.4.2
DTS Support
The EMC2104 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
CONTROL
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 T
CONTROL
or equal to 90°C.
Either or both of the Pushed Temperature Registers can be written with DTS data and used to control
the respective 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
for examples on using DTS data in the Look Up Table.
APPLICATION NOTE:
The device is designed with the assumption that T
CONTROL
is 100°C. As such, all DTS
related conversions are done based on this value including Look Up Table comparisons. If
T
CONTROL
is adjusted (i.e. T
CONTROL
is shifted to 105°C), then all of the Look Up Table
thresholds should be adjusted by a value equal to T
CONTROL
- 100°C.
5.5
RPM based Fan Speed Control Algorithm (FSC)
The EMC2104 includes antwo RPM based Fan Speed Control Algorithms. Each algorithm operates
independently and controls a separate fan driver.Each 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.
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.
Revision 1.74 (05-08-08)
28
SMSC EMC2104
DATASHEET
SMSC [ SMSC CORPORATION ]
