EMC6D103 datasheet(38/89 Pages) SMSC

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Fan Control Device with High Frequency PWM Support and Hardware Monitoring Features

Datasheet

Revision 0.4 (04-04-05)

SMSC EMC6D103

DATASHEET

Figure 7.2 Automatic Fan Control

7.1.3.3

Spin Up

When a fan is being started from a stationary state (PWM duty cycle =00h), the part will cause the fan

to “spin up” by going to 100% duty cycle for a programmable amount of time to overcome the inertia

of the fan (i.e., to get the fan turning). Following this spin up time, the fan will go to the duty cycle

computed by the auto fan algorithm.

During spin-up, the PWM duty cycle is reported as 0%.

To limit the spin-up time and thereby reduce fan noise, the part uses feedback from the tachometers

to determine when each fan has started spinning properly. The following tachometer feedback is

included into the auto fan algorithm during spin-up.

Auto Fan operation during Spin Up:

The PWM goes to 100% duty cycle until the tachometer reading register is below the minimum limit

(see Figure 7.3), or the spin-up time expires, whichever comes first. This causes spin-up to continue

until the tachometer enters the valid count range, unless the spin up time expires. If the spin up expires

before the tachometer enters the valid range, an interrupt status bit will be set once spin-up expires.

Note that more than one tachometer may be associated with a PWM, in which case all tachometers

associated with a PWM must be in the valid range for spin-up to end.

Temp

Time

Tmax

=Tmin

+Trange

Tmin

PWM

Duty

Cycle

Time

Max

=FFh

min

Spin-Up

Time

Hysteresis

Temperature

Temp

Time

Tmax

=Tmin

+Trange

Tmin

PWM

Duty

Cycle

Time

Max

=FFh

min

MIN/OFF bit = 0

(Fan off when temperature is below minimum)

MIN/OFF bit = 1

(Fan stays on when temperature is below minimum)

Notes:

1. When exiting spin-up, the PWM is set to the current calculated PWM

2. The PWM is set to OFF when the current temperature is less than

(Tmin-Hysteresis Temp)

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