Multiple RPM-Based PWM Fan Controller
Datasheet
Table 5.22 Spin Time
SPINUP_TIMEX[1:0]
1
0
0
1
1
0
0
1
0
1
TOTAL SPIN UP TIME
250 ms
500 ms (default)
1 sec
2 sec
5.13
Fan Max Step Registers
Table 5.23 Fan Max Step Registers
ADDR
37h
47h
57h
R/W
R/W
R/W
R/W
REGISTER
Fan 1 Max
Step
Fan 2 Max
Step
Fan 3 Max
Step
B7
-
-
-
B6
-
-
-
B5
32
32
32
B4
16
16
16
B3
8
8
8
B2
4
4
4
B1
2
2
2
B0
1
1
1
DEFAULT
10h
10h
10h
The Fan Max Step registers, along with the Update Time, control the ramp rate of the fan driver
response calculated by the RPM-based Fan Speed Control Algorithm. The value of the register
represents the maximum step size each fan driver will take between update times (see
When the FSC algorithm is enabled, Ramp Rate control is automatically used. When the FSC is not
active, then Ramp Rate control can be enabled by asserting the EN_RRC bit (see
APPLICATION NOTE:
The UPDATE bits and Fan Step Register settings operate independently of the RPM-based
Fan Speed Control Algorithm and will always limit the fan drive setting. That is, if the
programmed fan drive setting (either as determined by the RPM-based Fan Speed Control
Algorithm or by manual settings) exceeds the current fan drive setting by greater than the
Fan Step Register setting, the EMC2303 will limit the fan drive change to the value of the
Fan Step Register. It will use the Update Time to determine how often to update the drive
settings.
APPLICATION NOTE:
If the Fan Speed Control Algorithm is used, the default settings in the Fan Configuration 2
Register will cause the maximum fan step settings to be ignored.
The Fan Max Step registers are software locked.
SMSC EMC2303
39
Revision 1.1 (10-12-09)
DATASHEET
SMSC [ SMSC CORPORATION ]
