LM93 datasheet(32/92 Pages) NSC

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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:

The current duty cycle being requested by other PWM

functions is memorized.

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

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).

PWM

bound

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.

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