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Fan Speed Control with the EMC2102 Device
SMSC EMC2102
USER MANUAL Revision 0.2 (09-17-07)
23
5.5 Experiment 5 - Optimizing RPM Control Response
This experiment is designed to gain familiarity with the parameters that affect the closed-loop controller
implemented in the EMC2102. All these registers are located on the Fan Setting page in ChipMan.
This experiment will go through each register, examining the effects of parametric changes on the
closed-loop controller in RPM mode.
5.5.1 General Setup
For all these tests, the Fan Drive Setting register (51h), the TACH Target register (57h) and the TACH
Reading registers (58h) are selected to plot. As bits are switched in each of the tests, the register name
and address will be provided.
5.5.2 Fan Configuration Register (52h)
The Fan Configuration Register stores the basic operation parameters of the closed-loop controller.
The EN bit turns on the RPM controller, and locks out manual updates to the Fan Drive Setting register
(51h).
The next two parameters, LIMIT2K and EDGES[1:0] (both in register 52h) describe the fan itself. The
EDGES[1:0] tell the controller how many tach edges to examine to determine the fan speed. The
LIMIT2K parameter tells the RPM controller how to interpret the TACH Target register (57h). The value
of this parameter provides an operating range for the fan by specifying the minimum rpm: the 500 rpm
setting is for low speed fans and the 2000 rpm setting is typical for notebook and desktop fans (high
speed fans). (Please refer to Section 6.1, "DC Fan Basics - Poles, Tach Meter Pulses and Edges" for
more details about the TACH edges and ranges.)
For all experiments in this suite, the default values have been used. This keeps the scaling of those
values fixed, allowing the ChipMan application to appropriately scale the counts to RPM values.
The UPDATE[2:0] parameter controls the speed at which the RPM controller updates the output drive,
as already been discussed in Section 5.4, "Experiment 4 - RPM Drive Mode Rate Controls". This
parameter is independent of the TACH Reading updates, which are controlled by the EDGES[1:0]
parameter. The plots in Figure 5.19, "Update Time Modifications" show the effect of UPDATE on the
closed-loop performance when starting the on-board fan. The numbers (in unit of second) in the left
plot indicate the UPDATE value used for that sequence. By experimenting with the different update
times you can determine the most stable setting for the fan to be controlled.
Figure 5.19 Update Time Modifications
Invalid TACH signals
(Ignored by Controller)
0.1s 0.2s 0.4s 0.8s 1.6s