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Fan Speed Control with the EMC2102 Device
SMSC EMC2102
USER MANUAL Revision 0.2 (09-17-07)
17
the 60% drive the register 51h value is 153d or 99h, and for 75% it is 191d or BFh. Those two drive
settings will run a DC fan at two different speeds and we will call them rpm60 and rpm75. Depending
on the fan, the speed for the same drive setting will vary.
All data and plot examples in this document were taken using an EVB-EMC2102 board with the on-
board DC fan. This fan has an rpm60 of 4500 rpm, and an rpm75 of 5650 rpm.
5.3.2 Getting Started
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.
5.3.3 Forced Kick Function
The EMC2102 has a forced 100% kick at turn-on. This feature drives the fan at maximum voltage for
¼ of the time set by the SPINUP_TIME[1:0] bits in register 53h. The plots in Figure 5.12, "Forced Kick
Function" illustrate this function with a spin-up time of 2.0 sec while the TACH Target register (57h) is
changed from 0 rpm to 5200 rpm.
Selecting a different "Time per Division" value in the pull-down menu in the center bottom of the plotting
window, to make the 100% kick pulse can be viewed. This scale change affects both playback, and
real-time mode. The rate at which data is recorded is unaffected by changing this parameter.
5.3.4 Spin-Up Level
Depending on the application, the value of LEVEL (spin-up level, bit[1] in register 53h) may need to
be adjusted to achieve the best fan control result. The plots in Figure 5.13, "60% Spin Level Setting"
show the same experiment as Section 5.3.3, "Forced Kick Function" with a 60% spin-up level. Note
the a smaller overshoot at the lower LEVEL setting.
Figure 5.12 Forced Kick Function
100% Kick Pulse for 500 ms
(1/4 of Spin-Up Time)
Spin-Up
Time = 2 s
Normal Fan Drive
(for 5200 rpm)
75% Spin-Up
Level