PC8374L datasheet(136/239 Pages) NSC

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8.0 Health Management (HM) (Continued)

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Fan Force-On Conditions

In addition to setting the Constantly On fan mode option via the MODE field in the FANPWMn Control Configuration regis-

ters, the duty cycle of each FANPWM output is forced to the value contained in the associated FANPWMn MAX Duty register

in one of the following conditions:

• If the value in one of the temperature zones is above the value in its associated Zone ‘n’ Absolute Temperature Limit.

• If the FANPWM output is in automatic mode, and a communication error with the device containing the associated

temperature zone sensor is detected.

• If the FANPWM output is in automatic mode and one of the following occurs:

— The fan is associated with Temperature Zone1, and a Remote Diode Fault is detected.

— The fan is associated with Temperature Zone3, an LM96010 or LM96012 device is used, and a Remote Diode Fault

is detected.

— The Temperature Reading Zone ‘n’ register of its associated Temperature Zone, holds a value of 80h (temperature

measurement error).

• If a fan failure is detected, and the fan was neither stopped by conﬁguration (i.e., disabled) nor is spinning-up.

Note: For fans that are not connected or that do not have a tachometer output, make sure the related FANTACHn input is

not associated with any FANPWMn output by setting the respective ASSOCn ﬁeld in the Tach PWM Association

Speed Change Modes

For each FANPWMn output, in all four modes, the speed changes in one of two ways, as configured by the SPD_CHGn bit

in the Extended FANPWM Control Register 2 (see Section 8.5.86 on page 191):

• Hard speed-change: The FANPWM duty cycle is updated in one immediate step.

• Soft speed-change: The FANPWM duty cycle is changed in steps of 3.125% duty-cycle until the new duty-cycle is

reached. Changes between 0% and the minimum duty cycle (as defined in the FANPWMn Minimum registers) is done

in one immediate step (when the fan is stopping or spinning-up). The step duration is determined by the STEP_LEN

field in the Extended Control Configuration register. Figures 33 and 34 show a soft speed-change example.

There are two ways to end the spin-up process (configured by the SPIN_END bit in the Extended FANPWM Control Con-

figuration register:

• Time: The spin-up process is ended after the time period deﬁned in the SPIN ﬁeld in the FANPWMn Control Conﬁg-

uration Register

• Speed or time: The spin-up process is ended after the time period deﬁned in the SPIN ﬁeld in the FANPWMn Control

Conﬁguration Register or after the fan speed value (in the Fan Tachometer Reading ‘n’ LSB and MSB registers) is

either equal to or higher than the value in Fan Tachometer ‘n’ Low Limit LSB and MSB registers, whichever occurs

ﬁrst. Note that the FSTLMD bit in the associated Extended FANPWM Control register (see Section 8.5.85 on

page 190) must be set to 1.

When the spin-up process ends, the FANPWM duty cycle is set to one of the following values:

• The value set in FANPWMn Current Duty register, in Manual Fan Control mode

• The value generated from the current normalized temperature by the automatic algorithm, in Automatic Fan Control

mode (this value is updated in the FANPWMn Current Duty register)

• The value set in FANPWMn MAX Duty register, in Continuously On mode

When a speed-change follows the spin-up, the speed-change mode depends on the relation between the duty-cycle at the end

of the spin-up (“spin-end DC”) and the current duty-cycle that was generated by the automatic algorithm (PWM_DUTY field):

• If PWM_DUTY > spin-end DC, either a hard or a soft speed-change (according to the setting of SPD_CHNGn bit in

Extended FANPWM Control Register 2) is performed between the values of spin-end DC and PWM_DUTY.

• If PWM_DUTY < spin-end DC, a hard speed-change (one step) is performed between the values of spin-end DC and

PWM_DUTY.

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