EMC6D102_06 Datasheet, PDF (30/86 Pages) SMSC Corporation – Fan Control Device with Hardware Monitoring and Acoustic Noise Reduction Features

6.1.3.2
Fan Control Device with Hardware Monitoring and Acoustic Noise Reduction Features
Datasheet
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.
Auto Fan Control Operating Mode
The EMC6D102 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 6.1 Automatic Fan Control Flow Diagramon page 31).
PWM outputs are assigned to a thermal zone based on the PWMx Configuration registers (see Section
5.10, "Thermal Zones," on page 27). 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.
Revision 0.4 (06-15-06)
30
DATASHEET
SMSC EMC6D102