SMBus Fan Control with 1°C Accurate Temperature Monitoring
Datasheet
Where:
PWM_F is the setting of the PWM
Frequency register (4Dh)
360k
--------------------------------
1
5806
FREQ
⎛
⎝
⎞
-----------------
-----------------
PWM_D =
×
=
[5]
⎠
PWM_D is the setting of the PWM
Frequency Divide Register (4Eh)
2 × PWM_F
FREQ
FREQ is the desired PWM
Frequency
Maximum resolution is achieved by setting the PWM Frequency Register to 1Fh. With maximum
resolution, the desired PWM frequency can be achieved by adjusting the PWM Frequency Divide
Register setting (PWM_D[7:0]) as shown in Table 6.26.
For example, if the user desires a 30Hz PWM frequency with maximum PWM resolution, then the
PWM_F[4:0] bits should be set at 1Fh (31d) and the the PWM_D bits should be set at C1h (193d).
Table 6.26 Examples of Fan PWM Frequency with Maximum Resolution
PWM_F[4:0] = 1Fh
EFFECTIVE
DUTY CYCLE
(AT 50%
EFFECTIVE
DUTY CYCLE
(AT 75%
EFFECTIVE
RESOLUTION
(%)
FAN_SETTING
TO GET 75%
DUTY CYCLE
PWM_D[7:0]
SETTING
EFFECTIVE PWM
FREQUENCY (HZ)
FAN_SETTING) FAN_SETTING)
01h
11h
20h
47h
C0
1.61
1.61
1.61
1.61
1.61
1.61
1.61
51.6%
51.6%
51.6%
51.6%
51.6%
51.6%
51.6%
77.4%
77.4%
77.4%
77.4%
77.4%
77.4%
77.4%
2Eh (74.2%)
2Eh (74.2%)
2Eh (74.2%)
2Eh (74.2%)
2Eh (74.2%)
2Eh (74.2%)
2Eh (74.2%)
5806.5
341.6
181.5
81.8
30.2
C1
30.0
FFh
22.7
6.21
Fan Control Look-Up Table Hysteresis Register
Table 6.27 Look Up Table Hysteresis Register
ADDR.
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
Fan Control Look-
Up Table Hysteresis
04h
(4°C)
4Fh
R/W
-
-
-
16
8
4
2
1
The Fan Control Look-Up Table Hysteresis Register determines the amount of hysteresis applied to
the temperature inputs of the fan control Fan Control Look-Up Table. See Section 5.6.4.
Revision 2.53 (03-13-07)
SMSC EMC2101
DATA4S4HEET
SMSC [ SMSC CORPORATION ]
