EMC2302 datasheet(19/44 Pages) SMSC

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Dual RPM-Based PWM Fan Controller

Datasheet

SMSC EMC2302

Revision 1.1 (10-12-09)

DATASHEET

The FAN_STALL Status bit indicates that a stalled fan was detected. This bit is checked conditionally

depending on the mode of operation.

Whenever the Direct Setting Mode or the Spin Up Routine is enabled, the FAN_STALL interrupt

will be masked for the duration of the programmed Spin Up Time (see Table 5.22) to allow the fan

to reach a valid speed without generating unnecessary interrupts.

In Direct Setting Mode, whenever the TACH Reading Register value exceeds the Valid TACH Count

When using the RPM-based Fan Speed Control Algorithm, the stalled fan condition is checked

whenever the Update Time is met and the fan drive setting is updated. It is not a continuous check.

4.4.2

Aging Fan or Invalid Drive Detection

This is useful to detect aging fan conditions (where the fan’s natural maximum speed degrades over

time) or a speed setting that is faster than the fan is capable of. The EMC2302 contains circuitry that

detects that the programmed fan speed can be reached by the fan. If the target fan speed cannot be

reached within a user defined band of tach counts at maximum drive, the DRIVE_FAIL status bits are

set and the ALERT# pin is asserted.

4.5

CLK Pin

The CLK pin has multiple functionality as determined by the settings of the Configuration register.

4.5.1

External Clock

The EMC2302 allows the user to choose between supplying an external 32.768kHz clock or use of

the internal 32kHz oscillator to measure the tachometer signal. This clock source is used by the RPM-

based Fan Speed Control Algorithm to calculate the current fan speed. This fan controller accuracy is

directly proportional to the accuracy of the clock source.

When this function is used, the external clock is driven into the device via the CLK pin.

4.5.2

Internal Clock

Alternately, the EMC2302 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 EMC2302 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).

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