EMC6D103 datasheet(34/92 Pages) SMSC

34 / 92 page

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

Datasheet

Revision 0.3 (03-01-07)

SMSC EMC6D103

DATASHEET

When in manual mode, the current PWM duty cycle registers can be written to adjust the speed of the

fans, when the start bit is set. These registers are not writable when the lock bit is set.

Note: The PWMx Current Duty Cycle register is implemented as two separate registers: a read-only

and a write-only.

When a value is written to this register in manual mode there will be a delay

before the programmed value can be read back by software. The hardware updates the read-

only PWMx Current Duty Cycle register on the beginning of a PWM cycle. If Ramp Rate

Control is disabled, the delay to read back the programmed value will be from 0 seconds to

1/(PWM frequency) seconds. Typically, the delay will be 1/(2*PWM frequency) seconds.

7.1.3.2

Auto Fan Control Operating Mode

The EMC6D103 implements automatic fan control. In Auto Fan Mode, this device automatically adjusts

the PWM duty cycle of the PWM outputs, according to the flow chart on the following page (see

Figure 7.1 Automatic Fan Control Flow Diagramon page 35).

PWM outputs are assigned to a thermal zone based on the PWMx Configuration registers (see Section

6.10, "Thermal Zones," on page 31). It is possible to have more than one PWM output assigned to a

thermal zone. For example, PWM outputs 2 and 3, connected to two chassis fans, may both be

controlled by thermal zone 2. At any time, if the temperature of a zone exceeds its absolute limit, all

PWM outputs go to 100% duty cycle to provide maximum cooling to the system (except those fans

that are disabled or in manual mode).

It is possible to have a single fan controlled by multiple zones, turning on when either zone requires

cooling based on its individual settings.

A VCC POR resets all values to their initial or default states.

If the start bit is one, the Auto Fan Control block will evaluate the temperature in the zones configured

for each Fan in a round robin method. The Auto Fan Control block completely evaluates the zones for

all three fans in a maximum of 0.25sec.

EMC6D103 Datasheet(PDF) 34 Page - SMSC Corporation