emc2105 Standard Microsystems Corp., emc2105 Datasheet - Page 59

• Manufacturer Part Number: emc2105
• Description: Emc2105 Rpm-based High Side Fan Controller With Hardware Thermal Shutdown
• Manufacturer: Standard Microsystems Corp.

RPM-Based High Side Fan Controller with Hardware Thermal Shutdown
Datasheet
SMSC EMC2105
0
0
1
1
1
EDGES[1:0]
2
0
0
0
Bits 4-3 - EDGES[1:0] - determines the minimum number of edges that must be detected on the
TACHx signal to determine a single rotation. A typical fan measured 5 edges (for a 2-pole fan). For
more accurate tachometer measurement, the minimum number of edges measured may be increased.
Increasing the number of edges measured with respect to the number of poles of the fan will cause
the TACH Reading registers to indicate a fan speed that is higher or lower than the actual speed. In
order for the FSC Algorithm to operate correctly, the TACH Target must be updated by the user to
accommodate this shift. The Effective Tach Multiplier shown in
term that is applied to the Actual RPM to achieve the Reported RPM. It should only be applied if the
number of edges measured does not match the number of edges expected based on the number of
poles of the fan (which is fixed for any given fan).
Contact SMSC for recommended settings when using fans with more or less than 2 poles.
Bit 2-0 - UPDATE - determines the base time between fan driver updates. The Update Time, along
with the Fan Step Register, is used to control the ramp rate of the drive response to provide a cleaner
transition of the actual fan operation as the desired fan speed changes. The Update Time is set as
shown in
1
0
0
1
1
0
1
0
1
0
Table
RANGE[1:0]
UPDATE[2:0]
6.27.
MINIMUM TACH
1
0
0
1
Table 6.26 Minimum Edges for Fan Rotation
EDGES
3
5
7
9
Table 6.25 Range Decode
Table 6.27 Update Time
0
0
1
0
1
DATASHEET
1 pole
2 poles (default)
3 poles
4 poles
NUMBER OF FAN POLES
59
0
0
1
0
REPORTED MINIMUM
1000 (default)
RPM
2000
4000
500
Table 6.26
MULTIPLIER (BASED ON 2
UPDATE TIME
is used as a direct multiplier
EFFECTIVE TACH
100ms
200ms
300ms
POLE FANS)
Revision 1.74 (05-08-08)
TACH COUNT
MULTIPLIER
0.5
1.5
1
2
1
2
4
8