RPM-Based PWM Fan Controller
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.
‘0’ (default) - Ramp rate control is disabled. When the fan driver is operating in Direct Setting mode,
the fan 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, the fan
drive setting will follow the ramp rate controls as determined by the Fan Step and Update Time
settings. The maximum fan drive setting step is capped at the Fan Step setting and is updated
based on the Update Time as given by Table 5.13.
Bit 5 - GLITCH_EN - Disables the low pass glitch filter that removes high frequency noise injected on
the TACHx 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 Table 5.15.
Table 5.15 Derivative Options
DER_OPT[1:0]
1
0
OPERATION
0
0
No derivative options used
Basic derivative. The derivative of the error from
the current drive setting and the target is added
to the iterative Fan Drive Register setting (in
addition to proportional and integral terms)
(default)
0
1
Step derivative. The derivative of the error from
the current drive setting and the target is added
to the iterative Fan Drive Register setting and is
not capped by the Fan Step Register.
1
1
0
1
Both the basic derivative and the step derivative
are used effectively causing the derivative term to
have double the effect of the derivative term.
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.
Table 5.16 Error Range Options
ERR_RNG[1:0]
1
0
OPERATION
0
0
1
0
1
0
0 RPM (default)
50 RPM
100 RPM
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Revision 1.1 (10-12-09)
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