PC8374L datasheet(135/239 Pages) NSC

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8.0 Health Management (HM) (Continued)

Revision 1.1

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— The generated duty cycle is at its minimum at the low limit of the temperature, deﬁned by the Zone ‘n’ Temperature

Limit (see Section 8.5.63 on page 181 to Section 8.5.65). At, and below, this point the duty cycle is either 0% or an-

other minimum value (the value contained in the FANPWMn Minimum register; see Section 8.5.79 on page 189 to

Section 8.5.81). The decision to create a 0% duty-cycle or a minimum duty cycle other than 0% is made according

to the MIN_ENn bit in the Min/Off, Spike Smoothing 1 register (see Section 8.5.74 on page 186). Below this point, a

conﬁgurable hysteresis is applied by the HYSTn ﬁeld in the Zone1-Zone2, Zone3 Hysteresis registers; see

Section 8.5.69 on page 183 to Section 8.5.70.

— If the temperature rises above the low limit, and the FANPWM is at 0% duty cycle, a spin-up process takes place.

During spin-up the FANPWM output duty cycle is set to the value contained in the FANPWMn MAX Duty register (see

Section 8.5.82 on page 189 to Section 8.5.84). For more information on the spin-up process see “Speed Change

Modes” on page 136.

— Between the low-limit and a temperature value of low-limit + range (range is conﬁgured by the RANGE ﬁeld in the

Zone ‘n’ Auto Speed Range and FANPWM ‘n’ Frequency registers; see Section 8.5.71 on page 183 to

Section 8.5.73) the duty-cycle is changed linearly between a value of 0% and the value contained in the FANPWMn

MAX Duty register (MAX_PWM ﬁeld).

The sampled temperature data from each temperature zone is low-pass filtered to prevent temperature spikes from affecting

the FANPWM output duty cycle and thus to prevent spurious speed changes of the fans (which cause unpleasant noise).

The rise time of the filter (0% to 95% of the incoming temperature change) is defined by the FILTn_EN bit and TEMP_FILTn

ﬁeld in Min/Off, Spike Smoothing 1-2 registers (see Section 8.5.74 on page 186).

Figure 31. Temperature Normalization

Figure 32. Automatic Fan Control Algorithm

Temperature

Normalized

Temperature

Hysteresis

Range

0% (00h)

100% (7Fh)

Very Low

Temperature

Absolute

8 C

Limit

Temperature Range

Hysteresis

Very High

Temperature

Low

Limit

Temperature

Duty

Cycle

MAX_PWM

Minimum

Duty Cycle

Spin-Up

All Fans at

MAX_PWM Duty Cycle

Temperature Range

Normalized

Very Low

Temperature

Low

Limit

Temperature

Very High (Absolute)

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