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Fan Speed Control with the EMC2102 Device
Revision 0.2 (09-17-07)
USER MANUAL SMSC EMC2102
16
5.3 Experiment 3 - Spin-up Configuration Options
This experiment is designed to gain familiarity with the various spin-up options available in the
EMC2102 devices.
This experiment will discuss the effects of Spin-Up Time and Spin-Up Levels. These parameters are
important to ensure a valid start, while minimizing the turn-on overshoot for initial low RPM settings.
(More examples regarding these two parameters can be found in Section 5.7.1, "Repetitious Spin-up
Routine Caused by Incorrect Settings").
The CMF file for this experiment is the same as for Experiment 1, EMC2102_default.cmf.
5.3.1 Fan Control Parameters
The spin-up routine is a special algorithm that the EMC2102 uses to boot up the fan. In manual control
(open loop) mode, it is only invoked when starting from a ‘0’ value in the FAN Drive Setting register
51h.
In the RPM control (closed-loop) mode, the spin-up routine is invoked when the device is driving a
stalled fan to a valid target speed, i.e., the raw data value in register 57h (TACH Target) is smaller
than the one in register 56h (Valid TACH Count). During the normal operation while the fan is running,
the spin-up routine could also be invoked if the fan speed fell to below the valid fan speed, i.e, the raw
data value in register 58h (TACH Reading) is greater than the one in register 56h (Valid TACH Count),
since the fan will be considered as stalled by the controller.
There are several parameters that control the fan’s behavior during and after the spin-up routine, as
shown in Figure 5.11, "Fan Control Parameters".
When the spin-up routine is operating, the fan driver is set to full scale for one quarter of the total user
defined spin up time. For the remaining spin up time, the fan driver output is set a user defined level
(60% or 75% of full drive). After the spin-up routine has finished, the RPM algorithm controls the fan
speed to the TACH targets. At this point if the EMC2102 cannot detect a valid fan speed (the
hexadecimal value in the TACH Reading register is higher than the Valid TACH Count register setting,
which means the fan speed is below the valid speed), it will try to restart the fan.
The spin-up LEVEL (60% or 75%, defined by 53h[2]) has corresponding Fan Driver Setting
hexadecimal values (register 51h) which cab be calculated using FFh as 100% and 00h as 0%. For
Figure 5.11 Fan Control Parameters
100%
Spin Up Level =
60% ~ 75%
(53h[2])
Algorithm controlled drive
Fan Step
(54h[5:0])
Spin Up Time
(53h[1:0])
¼ of Spin Up Time
Update Time
(52h[2:0])
TACH Target
Changed
Target Count
Reached
New Target Count
Prev Drive
Check TACH
Use Spin-Up Algorithm
Use Normal
Closed-loop Algorithm
Fan Drive Setting
(51h)