Rainbow Electronics LM93 - Manual (Page 31)

15.0 Using The LM93
(Continued)
Note that since zones 1 and 2 share the same lookup table,
both zones must be operating in the same resolution mode.
The same applies to zones 3 and 4 since they share the
same lookup table.
15.10.3 Zone 1-4 to PWM1-2 Binding
Each zone must be bound to the PWM outputs in order to
have effect on the output’s duty cycle. Any combination of
the zones may be used to drive a PWM output, they are not
limited to the binding described in the previous example. For
instance zones 1, 2 and 4 may be bound to PWM1 while
zones 3 and 4 are bound to PWM2. Note that the duty cycle
levels in the lookup table are dependent on the PWM output
frequency assignment. Therefore, if PWM1 is assigned to a
high frequency and PWM2 is assigned to a low frequency, in
the binding example just mentioned, zone 4 has a different
duty cycle calculated through the lookup table for PWM1
than for PWM2, even though the same Toffset values are
used. This is due to the fact that PWM levels assigned to a
high frequency PWM output are different than the levels
assigned to a low frequency PWM output.
15.10.4 Fan Control Duty Cycles
Several registers in the LM93 use 4-bit values to represent a
duty cycle. All of them use a common mapping that associ-
ates the 4-bit value with a duty cycle. The 4-bit values
correspond also with the 14 steps of the auto fan control
algorithm. The mapping is shown below. This applies for
PWM outputs running at the default 22.5 kHz (high) fre-
quency.
4-Bit Value Step 22.5 kHz (High Frequency)
Duty Cycle
0h 0.00%
1h 1 25.00%
2h 2 31.25%
3h 3 37.50%
4h 4 43.75%
5h 5 50.00%
6h 6 56.25%
7h 7 62.50%
8h 8 68.75%
9h 9 75.00%
Ah 10 81.25%
Bh 11 87.50%
Ch 12 93.75%
Dh 13 100.00%
Eh — Reserved
Fh — Reserved
15.10.5 Alternate PWM Frequencies
The PWM output can operate at lower frequencies, instead
of the default 22.5 kHz. The alternate lower frequencies can
be enabled through the PWMx Control 4 registers. When
operating in the lower frequency mode, the mapping be-
tween step numbers and duty cycles changes. This effects
the auto fan control and all LM93 registers that describe a
duty cycle using a 4-bit value.
The low frequency PWM output duty cycle mapping is listed
in the following table:
4-Bit Value Step Low Frequencies
Duty Cycle
0h 0%
1h 1 25.00%
2h 2 28.57%
3h 3 32.14%
4h 4 35.71%
5h 5 39.29%
6h 6 42.86%
7h 7 46.43%
8h 8 50.00%
9h 9 53.57%
Ah 10 57.14%
Bh 11 71.43%
Ch 12 85.71%
Dh 13 100.00%
Eh — Reserved
Fh — Reserved
15.10.6 Fan Control Priorities
The automatic fan control is not the only function that influ-
ences PWM duty cycle. There are several other functions
that influence the PWM duty cycle. All the functions can be
classified into several categories:
Category
#
Category Name
1 PWM to 100% conditions
2 VRDx_HOT ramp-up/ramp-down
3 PROCHOT ramp-up/ramp-down function
4 Manual PWM Override
5 Fan Spin-Up Control
6 Automatic Fan Control Algorithm
The ultimate PWM duty cycle that is chosen can be de-
scribed by the following formula:
If (Manual PWM Override is active)
PWM = max(1,2,3,4)
Else
PWM = max(1,2,3,5,6)
So in general, categories 1, 2 and 3 are always active. In
addition to that, either category 4 or categories 5 and 6 are
active depending on whether manual override is enabled. In
this sense the manual override, when enabled, replaces
category 5 and 6.
15.10.7 PWM to 100% Conditions
There are several conditions that cause the duty cycles of all
PWM outputs to immediately get set to 100%. They are:
1. Any of the four temperature zones has exceeded the
programmed Fan Boost Limit setting but has not yet
cooled down enough to drop below the hysteresis point.
2. The OVRID bit is set in the LM93 Status/Control.
LM93
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