Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
Each temperature (or voltage) channel threshold shares the same hysteresis value. When the
measured temperature for any of the channels meets or exceeds the programmed threshold, the drive
setting associated with that threshold is used. The temperature must drop below the threshold minus
the hysteresis value before the drive setting will be set to the previous value.
APPLICATION NOTE: For proper operation, the hysteresis must be smaller than the difference between two
consecutive thresholds.
If the RPM based Fan Speed Control Algorithm is used, the TACH Target is updated after every
conversion. It is always set to the minimum TACH Target that is stored by the Look Up Table. The fan
drive setting cycle is updated based on the RPM based Fan Speed Control Algorithm configuration
settings.
If the RPM based Fan Speed Control Algorithm is not used, then the fan drive setting is updated after
every conversion. It is set to the maximum duty cycle that is stored by the Look Up Table.
6.34
Look Up Table 2 Registers
Table 6.51 Look Up Table2 Registers
TACH /
DRIVE
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
‘0’
‘1’
4096
128
2048
64
1024
32
512
16
256
8
128
4
64
2
32
1
FBh
FBh
LUT 2 Drive
Setting 1
91h
R/W
LUT 2 Ext
Diode 1
Setting 1
7Fh
(127°C)
X
X
X
-
752.9
-
64
376.5
64
32
188.2
32
16
94.12
16
8
47.06
8
4
23.53
4
2
11.76
2
1
5.88
1
92h
R/W
LUT2 VIN1
Setting 1
7Fh
(0.4V)
LUT 2 Ext
Diode 2
Setting 1
7Fh
(127°C)
93h
94h
R/W
R/W
LUT2 VIN2
Setting 1
7Fh
(0.4V)
X
X
X
X
752.9
376.5
64
188.2
32
94.12
16
47.06
8
23.53
4
11.76
2
5.88
1
LUT 2 Temp
3 Setting 1
7Fh
(127°C)
-
752.9
-
LUT2 Voltage
3 Setting 1
7Fh
(0.4V)
376.5
64
188.2
32
94.12
16
47.06
8
23.53
4
11.76
2
5.88
1
LUT2 Temp 4
Setting 1
7Fh
(127°C)
95h
...
R/W
...
...
...
‘0’
‘1’
...
...
2048
64
...
1024
32
...
512
16
...
256
8
...
128
4
...
64
2
...
32
1
...
4096
128
92h
LUT 2 Drive
Setting 8
B4h
R/W
LUT 2 Ext
Diode 1
Setting 8
7Fh
(127°C)
X
X
-
64
32
16
8
4
2
1
B5h
R/W
LUT2 VIN1
Setting 8
7Fh
(0.4V)
752.9
376.5
188.2
94.12
47.06
23.53
11.76
5.88
Revision 1.74 (05-08-08)
SMSC EMC2104
DATA7S8HEET
SMSC [ SMSC CORPORATION ]
