Multiple RPM-Based PWM Fan Controller
Datasheet
Controls the base frequency of PWM drivers 1-3
Bits 5-6 - PWM_BASE3[1:0] - Determines the base frequency of the PWM3 driver.
Bits 3-2 - PWM_BASE2[1:0] - Determines the base frequency of the PWM2 driver.
Bits 1-0 - PWM_BASE1[1:0] - Determines the base frequency of the PWM1 driver.
Table 5.7 PWM_BASEx[1:0] Bit Decode
PWM_BASEX[1:0]
1
0
0
1
1
0
0
1
0
1
BASE FREQUENCY
26.00kHz (default)
19.531kHz
4,882Hz
2,441Hz
5.7
Fan Setting Registers
Table 5.8 Fan Driver Setting Registers
ADDR
30h
40h
50h
R/W
R/W
R/W
R/W
REGISTER
Fan 1 Setting
Fan 2 Setting
Fan 3 Setting
B7
128
128
128
B6
64
64
64
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
00h
00h
00h
The Fan Setting register always displays the current setting of the respective fan driver. Reading from
any of the registers will report the current fan speed setting of the appropriate 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 is active, the register is read only. Writing to the
register will have no effect and the data will not be stored.
The contents of the register represent the weighting of each bit in determining the final output voltage.
The output drive for a PWM output is given by
VALUE
-
Drive
=
⎛
--------------------
⎞ ×
100%
⎝
255
⎠
[1]
Revision 1.1 (10-12-09)
32
SMSC EMC2303
DATASHEET
SMSC [ SMSC CORPORATION ]
