RPM-Based PWM Fan Controller
Datasheet
Table 5.22 Spin Time
SPINUP_TIME[1:0]
1
0
TOTAL SPIN UP TIME
0
0
1
1
0
1
0
1
250 ms
500 ms (default)
1 sec
2 sec
5.13
Fan Max Step Register
Table 5.23 Fan Max Step Register
ADDR
37h
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
R/W
Fan Max Step
-
-
32
16
8
4
2
1
10h
The Fan Max Step register, along with the Update Time, controls 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 the fan driver will take between update times (see Section 5.9).
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 Section 5.10).
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 EMC2301 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 register is software locked.
5.14
Fan Minimum Drive Register
Table 5.24 Minimum Fan Drive Register
ADDR
38h
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
Fan Minimum
Drive
66h
(40%)
R/W
128
64
32
16
8
4
2
1
The Fan Minimum Drive register stores the minimum drive setting for the RPM-based Fan Speed
Control Algorithm. The RPM-based Fan Speed Control Algorithm will not drive the fan at a level lower
than the minimum drive unless the target Fan Speed is set at FFh (see Section 5.17).
Revision 1.1 (10-12-09)
SMSC EMC2301
DATA3S4HEET
SMSC [ SMSC CORPORATION ]
