EMC2303 datasheet(21/51 Pages) SMSC

21 / 51 page

Multiple RPM-Based PWM Fan Controller

Datasheet

SMSC EMC2303

Revision 1.1 (10-12-09)

DATASHEET

4.5.3

Internal Clock

Alternately, the EMC2303 may be configured to use its internal clock as a clock output to drive other

fan driver devices. When configured to operate in this mode, the device uses its internal clock for

tachometer reading and drives the CLK pin using a push-pull driver.

4.6

Spin Up Routine

The EMC2303 also contains programmable circuitry to control the spin up behavior of the fan driver

to ensure proper fan operation.

The Spin Up Routine is initiated in Direct Setting mode when the setting value changes from 00h to

anything else.

When the Fan Speed Control Algorithm is enabled, the Spin Up Routine is initiated under the following

conditions:

1. The TACH Target Register value changes from a value of FFh to a value that is less than the Valid

TACH Count (see Section 5.15).

2. The RPM-based Fan Speed Control Algorithm’s measured TACH Reading Register value is greater

than the Valid TACH Count setting.

When the Spin Up Routine is operating, the fan driver is set to full scale (optional) for one quarter of

the total user defined spin up time. For the remaining spin up time, the fan driver output is set at a

user defined level (30% through 65% drive).

After the Spin Up Routine has finished, the EMC2303 measures the TACHx signal. If the measured

TACH Reading Register value is higher than the Valid TACH Count Register setting, the FAN_SPIN

status bit is set and the Spin Up Routine will automatically attempt to restart the fan.

Figure 4.2 shows an example of the Spin Up Routine in response to a programmed fan speed change

based on the first condition above.

EMC2303 Datasheet(PDF) 21 Page - SMSC Corporation