EMC2112 datasheet(21/65 Pages) SMSC

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RPM-Based Linear Fan Controller with Hardware Thermal Shutdown

Datasheet

SMSC EMC2112

Revision 0.88 (11-20-09)

DATASHEET

5.1

Fan Control Modes of Operation

The EMC2112 has two modes of operation for the 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 6.17) will instantly update the fan drive.

Ramp Rate control is optional and enabled via the EN_RRC bits.

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.

5.2

RPM-Based Fan Speed Control Algorithm (FSC)

The EMC2112 includes a RPM-based Fan Speed Control Algorithm for the fan driver.

This fan control algorithm uses Proportional, Integral, and Derivative terms to automatically approach

and maintain the system’s desired fan speed to an accuracy directly proportional to the accuracy of

the clock source.

The desired tachometer count is set by the user inputting the desired number of 32.768KHz cycles

that occur per fan revolution. This is done by setting the TACH Target Register. The user may change

the target count at any time. The user may also set the target count to FFh in order to disable the fan

driver for lower current operation.

Table 5.1 Fan Controls Active for Operating Mode

DIRECT SETTING MODE

FSC MODE

Fan Driver Setting (read / write)

Fan Driver Setting (read only)

EDGES[1:0]

(Fan Configuration)

RANGE[1:0]

(Fan Configuration)

UPDATE[2:0]

(Fan Configuration)

UPDATE[2:0]

(Fan Configuration)

LEVEL

(Spin Up Configuration)

LEVEL

(Spin Up Configuration)

SPINUP_TIME[1:0]

(Spin Up Configuration)

SPINUP_TIME[1:0]

(Spin Up Configuration)

Fan Max Step

Fan Minimum Drive

Valid TACH Count

TACH Target (read / write)

TACH Reading

DRIVE_FAIL_CNT[1:0] and Drive Band Fail Registers

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