EMC2101 Datasheet, PDF (44/55 Pages) SMSC Corporation – SMBus Fan Control with 1°C Accurate Temperature Monitoring

SMBus Fan Control with 1°C Accurate Temperature Monitoring
Datasheet
PWM_D
=
⎛
⎝
2^-----×^-----P^3----6W^---0---M^-k-----_^----F^{--⎠⎞}
×
--------¹---------
FREQ
=
---⁵---⁸---⁰----⁶----
FREQ
Where:
PWM_F is the setting of the PWM
Frequency register (4Dh)
PWM_D is the setting of the PWM
[5]
Frequency Divide Register (4Eh)
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
PWM_D[7:0]
SETTING
01h
11h
20h
47h
C0
C1
FFh
EFFECTIVE
RESOLUTION
(%)
1.61
1.61
1.61
1.61
1.61
1.61
1.61
EFFECTIVE
DUTY CYCLE
(AT 50%
FAN_SETTING)
EFFECTIVE
DUTY CYCLE
(AT 75%
FAN_SETTING)
FAN_SETTING
TO GET 75%
DUTY CYCLE
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%)
EFFECTIVE PWM
FREQUENCY (HZ)
5806.5
341.6
181.5
81.8
30.2
30.0
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
4Fh
R/W
Fan Control Look-
Up Table Hysteresis
-
-
-
16 8
4
2
1
04h
(4°C)
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)
44
DATASHEET
SMSC EMC2101