SMSC EMC2102 Manuale Utente

Fan Speed Control with the EMC2102 Device

Revision 0.2 (09-17-07)

SMSC EMC2102

36

 

Note: Although users can set the number of edges (in register 52h) to either 3, 5, 7 or 9, it is strongly

recommended using the default value 5 while driving a 2-pole DC fan. This equal to one
complete fan revolution for a 2-pole fan.

ChipMan translates TACH counts to the RPM value and displays the fan speed. For applications not
using ChipMan software, the following equation can be used to convert the TACH Reading values to
the real RPM speeds.

As a very important component in the closed-loop, the DC fan’s characteristics have a great impact
on the control system’s performance. Using the EVB-EMC2102 and ChipMan software tool, a 5V DC
fan’s characteristics can be easily tested.

In general, the following parameters need to be characterized:

„

Minimum Startup Speed

„

Stall Speed 

„

Minimum Valid TACH Speed

„

Maximum Fan Speed

„

Spin-up Level (i.e., rpm60 and rpm75. Refer to 

 for more 

details)

„

Setup the system and make sure the hardware and software are working as discussed in 

.

„

Unplug the on-board DC fan from connector P1

„

Connect the DC fan to be tested to P1 (refer to EVB-EMC2102 User Manual for the DC fan 
connector pinouts)

where:

EDGES = number of edges set by register 52h[4:3]

COUNT = TACH Reading (58h) value

Poles = number of pole pairs in the DC fan

m = factor defined by LIMIT2K (52h[6])
(m = 1 for 500 rpm and m = 4 for 2000 rpm)

Fan Tach Signal

3 EDGES

5 EDGES

7 EDGES

32.768kHz 

Clock

n-EDGE WINDOW

T

WINDOW

*

983040

*

1

−

=