EMC2104 datasheet(68/101 Pages) SMSC

68 / 101 page

Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown

Datasheet

Revision 1.74 (05-08-08)

SMSC EMC2104

DATASHEET

Bit 2 - 1 - ERR_RNGx[1:0] - Control some of the advanced options that affect the error window. When

the measured fan speed is within the programmed error window around the target speed, then the fan

drive setting is not updated. The algorithm will continue to monitor the fan speed and calculate

necessary drive setting changes based on the error, however these changes are ignored.

Bit 0 - LOWDRIVEx - Determines whether the tachometer measurement circuit will use the Tach Period

Measurement method of fan speed measurement or the Tach Pulse Count Method of fan speed

measurement. Setting this bit allows the use of low side fan drive circuits as shown in Figure 6.1

without requiring additional tachometer recovery circuitry.

‘0’ (default) - The tachometer signal must always be present when measuring the fan speed

regardless of the measurement method.

‘1’ - Low side PWM drive circuits are supported and the tachometer signal does not need to be

present at all times (which is common with such drive techniques). The tachometer measurement

circuitry will use the Tach Pulse Count Method to determine the fan speed (contact SMSC for

details on this operation). All tachometer related data is in the form of edge counts over a fixed

time period. This method is significantly slower and the tachometer updates are non-continuous.

Table 6.34 Error Range Options

ERR_RNGX[1:0]

OPERATION

0 RPM (default)

50 RPM

100 RPM

200 RPM

Figure 6.1 LOWDRIVE Supported Drive Circuit

PWM Input

EMC2104 Fiches technique(PDF) 68 Page - SMSC Corporation