RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
The Fan Configuration 2 Register controls the tachometer measurement and advanced features of the
RPM based Fan Speed Control Algorithm.
Bit 6 - EN_RRC - Enables ramp rate control when the fan driver is operated in the Direct Setting mode
or the Direct Setting with LUT mode.
‘0’ (default) - Ramp rate control is disabled. When the fan driver is operating in Direct Setting mode
or Direct Setting with LUT mode, the PWM setting will instantly transition to the next programmed
setting.
‘1’ - Ramp rate control is enabled. When the fan driver is operating in Direct Setting mode or Direct
Setting with LUT mode, the PWM setting will follow the ramp rate controls as determined by the
Fan Step and Update Time settings. The maximum PWM step is capped at the Fan Step setting
and is updated based on the Update Time as given by
Bit 5 - GLITCH_EN - Disables the low pass glitch filter that removes high frequency noise injected on
the TACH pin.
‘0’ - The glitch filter is disabled.
‘1’ (default) - The glitch filter is enabled.
Bits 4 - 3 - DER_OPT[1:0] - Control some of the advanced options that affect the derivative portion of
the RPM based Fan Speed Control Algorithm as shown in
Note that the default derivative
options disable the ramp rate control maximum step settings. To take advantage of the full ramp rate
control, limit derivative options to the disabled or basic derivative settings.
Table 6.34 Derivative Options
DER_OPT[1:0]
1
0
0
0
OPERATION
No derivative terms used
Basic derivative. The derivative of the error from
the current drive setting and the target is added
to the iterative Fan Drive setting (in addition to
proportional and integral terms)
Step derivative. The derivative of the error from
the current drive setting and the target is added
to the iterative Fan Drive setting and is not
capped by the maximum Fan Step Register
setting.
Both the basic derivative and the step derivative
are used effectively causing the derivative term to
have double the effect of the derivative term
(default).
0
1
1
0
1
1
Bit 2 - 1 - ERR_RNG[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.
SMSC EMC2103
57
Revision 0.85 (01-29-08)
DATASHEET
SMSC [ SMSC CORPORATION ]
