Multiple RPM-Based PWM Fan Controller for Five Fans
Datasheet
Contact SMSC for recommended settings when using fans with more or less than 2 poles.
Table 5.12 Minimum Edges for Fan Rotation
EDGESX[1:0]
EFFECTIVE TACH
MULTIPLIER (BASED ON 2
POLE FANS)
MINIMUM TACH
EDGES
1
0
NUMBER OF FAN POLES
0
0
1
1
0
1
0
1
3
5
7
9
1 pole
0.5
1
2 poles (default)
3 poles
1.5
2
4 poles
Bit 2-0 - UPDATEx[2:0] - 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 Table 5.13.
Table 5.13 Update Time
UPDATEX[2:0]
2
1
0
UPDATE TIME
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
100ms
200ms
300ms
400ms (default)
500ms
800ms
1200ms
1600ms
5.10
Fan Configuration 2 Registers
Table 5.14 Fan Configuration 2 Registers
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
Fan 1
Configuration 2
EN_
RRC1
GLITCH_
EN1
33h
R/W
-
DER_OPT1 [1:0]
DER_OPT2 [1:0]
DER_OPT3 [1:0]
ERR_RNG1[1:0]
ERR_RNG2[1:0]
ERR_RNG3[1:0]
-
28h
Fan 2
Configuration 2
EN_
RRC2
GLITCH_
EN2
43h
53h
R/W
R/W
-
-
-
-
28h
28h
Fan 3
Configuration 2
EN_
RRC3
GLITCH_
EN3
Revision 1.1 (10-12-09)
SMSC EMC2305
DATA3S8HEET
SMSC [ SMSC CORPORATION ]
