RPM-Based Fan Controller with Multiple Temperature Zones & Hardware Thermal Shutdown
Datasheet
7.22
Fan Setting Registers
Table 7.30 Fan Driver Setting Register
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
40h
R/W
Fan Setting
128
64
32
16
8
4
2
1
00h
The Fan Setting Register always displays the current setting of the Fan Driver. Reading from the
register will report the current fan speed setting of the fan driver regardless of the operating mode.
Therefore it is possible that reading from this register will not report data that was previously written
into this register.
While the RPM-based Fan Speed Control Algorithm and/or the Look Up Table are active, then the
register is read only. Writing to the register will have no effect and the data will not be stored.
If both the RPM-based Fan Control Algorithm and the Look Up Table are disabled, then the register
will be set with the previous value that was used. The register is read / write and writing to this register
will affect the fan speed.
The contents of the register represent the weighting of each bit in determining the final duty cycle. The
output drive for a PWM output is given by Equation [2].
VALUE
255
[2]
⎛
⎝
⎞
⎠
--------------------
Drive =
× 100%
7.23
PWM Divide Register
Table 7.31 PWM Divide Register
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
41h
R/W
PWM Divide
128
64
32
16
8
4
2
1
01h
The PWM Divide Register determines the final frequency of the PWM driver. The driver base frequency
is divided by the value of the PWM Divide Register to determine the final 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 final PWM frequency is derived as the base frequency divided by the value of this register as
shown in Equation [3].
PWM base freqeuncy
PWM Divide Setting
--------------------------------------------------------------
fPWM
=
[3]
7.24
Fan Configuration 1 Register
Table 7.32 Fan Configuration 1 Register
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
Fan
EN_
42h
R/W
RANGE[1:0]
EDGES[1:0]
UPDATE[2:0]
2Bh
Configuration 1 ALGO
Revision 1.2 (10-08-09)
SMSC EMC2113
DATA5S8HEET
SMSC [ SMSC CORPORATION ]
