EMC2302 Standard Microsystems Corp., EMC2302 Datasheet - Page 30

• Manufacturer Part Number: EMC2302
• Description: Rpm-based Pwm Fan Controller
• Manufacturer: Standard Microsystems Corp.

ADDR
32h
42h
Revision 1.2 (03-22-10)
5.9
R/W
R/W
R/W
frequency. The duty cycle settings are not affected by these settings, only the final frequency of the
PWM driver. A value of 00h will be decoded as 01h.
The Fan Configuration 1 registers control the general operation of the RPM-based Fan Speed Control
Algorithm used for the respective Fan Driver.
Bit 7 - EN_ALGOx - enables the RPM-based Fan Speed Control Algorithm.
Bits 6- 5 - RANGEx[1:0] - Adjusts the range of reported and programmed tachometer reading values.
The RANGE bits determine the weighting of all TACH values (including the Valid TACH Count, TACH
Target, and TACH reading) as shown in
Bits 4-3 - EDGESx[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.
Fan Configuration 1 Registers
1
0
0
1
1
‘0’ - (default) the control circuitry is disabled and the fan driver output is determined by the Fan
Driver Setting Register.
‘1’ - the control circuitry is enabled and the Fan Driver output will be automatically updated to
maintain the programmed fan speed as indicated by the TACH Target Register.
Configuration 1
Configuration 1
REGISTER
RANGEX[1:0]
Fan 1
Fan 2
Table 5.10 Fan Configuration 1 Registers
ALGO1
ALGO2
EN_
EN_
B7
Table 5.11 Range Decode
0
0
1
0
1
DATASHEET
RANGE1[1:0]
RANGE2[1:0]
B6
Table
30
B5
5.11.
REPORTED MINIMUM
EDGES1[1:0]
EDGES2[1:0]
B4
1000 (default)
RPM
2000
4000
500
B3
Table 5.12
Dual RPM-Based PWM Fan Controller
B2
UPDATE1[2:0]
UPDATE2[2:0]
is used as a direct multiplier
B1
TACH COUNT
MULTIPLIER
B0
SMSC EMC2302
1
2
4
8
Datasheet
DEFAULT
2Bh
2Bh