Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
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.
Table 6.34 Error Range Options
ERR_RNGX[1:0]
1
0
OPERATION
0
0
1
1
0
1
0
1
0 RPM (default)
50 RPM
100 RPM
200 RPM
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.
PWM Input
Figure 6.1 LOWDRIVE Supported Drive Circuit
Revision 1.74 (05-08-08)
SMSC EMC2104
DATA6S8HEET
SMSC [ SMSC CORPORATION ]
