EMC2104 datasheet(25/101 Pages) SMSC

25 / 101 page

Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown

Datasheet

SMSC EMC2104

Revision 1.74 (05-08-08)

DATASHEET

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’

115

698

115

147

7870

116

750

116

148

9090

117

787

117

149

10700

118

845

118

150

12700

119

909

119

151

15800

120

953

120

152

20500

121

1020

121

153

29400

122

1100

122

154

49900

123

1150

Open

Table 5.2 TRIP_SET Resistor Setting (continued)

TTRIP (°C)

LOW RANGE

TTRIP (°C)

HIGH RANGE

RSET (1%)

TTRIP (°C)

LOW RANGE

TTRIP (°C)

HIGH RANGE

RSET (1%)

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