Rainbow Electronics LM93 - Manual (Page 32)

15.0 Using The LM93
(Continued)
15.10.8 VRDx_HOT Ramp-Up/Ramp-Down
This function causes the duty cycle of the PWM outputs to
gradually increase over time if VRD1_HOT or VRD2_HOT
are asserted.
When VRDx_HOT is asserted, the ramp function is enabled.
The enabling process involves two steps:
1. The current duty cycle being requested by other PWM
functions is memorized.
2. The ramp function immediately adds one PWM duty
cycle step to the memorized value and requests this
duty cycle.
Once the function is enabled, it gradually adds additional
duty cycle steps every X milliseconds whenever VRDx_HOT
is asserted (X is programmable via the PWM Ramp Control
register). If VRDx_HOT remains asserted for a long enough
time, the duty cycle eventually reaches 100%.
Whenever VRDx_HOT is de-asserted, the ramp function
begins to ramp down by subtracting one PWM duty cycle
step every X milliseconds. If VRDx_HOT is currently de-
asserted, and the ramp function is less than to the PWM duty
cycle being requested by other functions, the ramp function
is disabled.
As long as the function is enabled, it continues to ramp up or
ramp down depending on the state of VRDx_HOT. The ramp
enabling process described above can only re-occur after
the ramp function has been disabled. Rapid assertion/de-
assertion of VRDx_HOT does not trigger the enabling pro-
cess unless VRDx_HOT was de-asserted long enough for
the ramp function to disable itself.
This ramp function operates independently for VRD1_HOT
and VRD2_HOT. In addition, the ramp function only applies
to the PWM(s) that are bound to one or two VRDx_HOT
inputs. Depending on the bindings, it is possible that up to
four independent ramp functions are active at any given
moment:
PWM1/VRD1
PWM1/VRD2
PWM2/VRD1
PWM2/VRD2
If a PWM is bound to both VRD1_HOT and VRD2_HOT,
then two ramp functions are active for that PWM output. In
this case the duty cycle that is used is the maximum of the
two ramp functions.
15.10.9 PROCHOT Ramp-Up/Ramp-Down
This function is very similar to the VRDx_HOT ramp-up/
ramp-down function. The PWM duty cycle ramps up in the
same fashion whenever the PROCHOT measurement ex-
ceeds the user programmed threshold. Once a new
PROCHOT measurement is made that no longer exceeds
the user limit, the PWM will begin to ramp down.
Just as with the VRDx_HOT ramp function, the PROCHOT
ramp function uses independent bindings to determine which
PWM outputs should be effected by each PROCHOT input
(P1_PROCHOT or P2_PROCHOT).
If a PWM is bound to both P1_PROCHOT and
P2_PROCHOT, two PROCHOT ramp functions could be
active at the same time. In this case the duty cycle that is
used is the maximum of the two ramp functions.
15.10.10 Manual PWM Override
When a PWM channel is configured for manual PWM over-
ride, software can manually control the PWM duty cycle.
There are some PWM control functions that could still cause
the duty cycle to be higher than the manual setting. See the
Section 15.10.6 Fan Control Priorities for details.
15.10.11 Fan Spin-Up Control
All of the other PWM control functions are combined to
produce a final duty cycle that is actually used for the PWM
output. If this final value changes from zero to a non-zero
value, the Fan Spin-Up Control function is triggered. Once
triggered, the Fan Spin-Up Control requests the pro-
grammed duty cycle for a programmed period of time.
LM93
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