RPM-Based PWM Fan Controller
Datasheet
5.6
PWM Base Frequency Register
Table 5.6 PWM Base Frequency Register
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
PWM_ PWM_
PWM Base
Frequency
2Dh
R/W
-
-
-
-
-
-
BASE
_1
BASE
_0
00h
The PWM Base Frequency register determines the base frequency that is used with the PWM Divide
register to determine the final PWM frequency. The PWM frequency is set by the base frequency and
its respective divide ratio (see Section 5.8).
Controls the base frequency of the PWM driver
Bits 1-0 - PWM_BASE1[1:0] - Determines the base frequency of the PWM driver.
Table 5.7 PWM_BASEx[1:0] Bit Decode
PWM_BASEX[1:0]
1
0
BASE FREQUENCY
0
0
1
1
0
1
0
1
26.00kHz (default)
19.531kHz
4,882Hz
2,441Hz
5.7
Fan Setting Register
Table 5.8 Fan Driver Setting Register
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
30h
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 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 Equation [1].
VALUE
⎛
⎝
⎞
--------------------
Drive =
× 100%
[1]
⎠
255
Revision 1.1 (10-12-09)
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