Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
Table 5.2 TRIP_SET Resistor Setting (continued)
TTRIP (°C)
LOW RANGE
TTRIP (°C)
HIGH RANGE
TTRIP (°C)
LOW RANGE
TTRIP (°C)
HIGH RANGE
RSET (1%)
RSET (1%)
83
84
85
86
87
88
89
90
91
115
116
117
118
119
120
121
122
123
698
750
115
116
117
118
119
120
121
122
60
147
148
149
150
151
152
153
154
92
7870
9090
787
10700
12700
15800
20500
29400
49900
Open
845
909
953
1020
1100
1150
5.2
Fan Control Modes of Operation
The EMC2104 has four modes of operation for each fan driver. Each mode of operation uses the Ramp
Rate control and Spin Up Routine.
1. Direct Setting Mode- in this mode of operation, the user directly controls the fan drive setting.
Updating the Fan Driver Setting Register (see Section 6.20) will instantly update the fan drive.
Ramp Rate control is optional and enabled via the EN_RRC bits.
This is the default mode. The Direct Setting Mode is enabled by clearing the LUT_LOCK bit
in the Look Up Table Configuration Register (see Section 6.32) while the TACH / DRIVE bit
is set to ‘0’.
Whenever the Direct Setting Mode is enabled the current drive will be changed to what was
last written into the Fan Driver Setting Register.
2. Fan Speed Control Mode (FSC) - in this mode of operation, the user determines a target
tachometer count and the drive setting is automatically updated to achieve this target speed. The
algorithm uses the Spin Up Routine and has user definable ramp rate controls.
This mode is enabled by clearing the LUT_LOCK bit in the Look Up Table (LUT)
Configuration Register and setting the EN_ALGO bit in the Fan Configuration Register.
3. Using the Look Up Table with Fan Drive Settings (Direct Setting w/ LUT Mode) - In this mode of
operation, the user programs the Look Up Table with fan drive settings and corresponding
temperature thresholds. The fan drive is set based on the measured temperatures and the
corresponding drive settings. Ramp Rate control is optional and enabled via the EN_RRC bits.
This mode is enabled by programming the Look Up Table then setting the LUT_LOCK bit
while the TACH / DRIVE bit is set to ‘1’.
The TACH / DRIVE bit in the Look Up Table Configuration Register MUST be set to ‘1’ or
the fan drive settings will be incorrectly set. Setting this bit to ‘1’ ensures the settings will be
PWM settings.
4. Using the Look Up Table with RPM Target Settings (FSC w/ LUT Mode) - In this mode of operation,
the user programs the Look Up Table with TACH Target values and corresponding temperature
thresholds. The TACH Target will be set based on the measured temperatures and the
corresponding target settings. The fan drive settings will be determined automatically based on the
RPM based Fan Speed Control Algorithm
This mode is enabled by programming the Look Up Table then setting the LUT_LOCK bit
while the TACH / DRIVE bit is set to ‘0’
SMSC EMC2104
Revision 1.74 (05-08-08)
DATA2S5HEET
SMSC [ SMSC CORPORATION ]
