EMC2302 datasheet(17/44 Pages) SMSC

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Dual RPM-Based PWM Fan Controller

Datasheet

SMSC EMC2302

Revision 1.1 (10-12-09)

DATASHEET

4.2

PWM Fan Driver

The EMC2302 supports 2 PWM output drivers. Each output driver can be configured to operate as an

open-drain (default) or push-pull driver and each driver can be configured with normal or inverse

polarity. Additionally, the PWM frequencies are independently programmable with ranges from 9.5Hz

to 26kHz in four programmable frequency bands.

4.3

RPM-based Fan Speed Control Algorithm (FSC)

The EMC2302 includes 2 RPM-based Fan Speed Control Algorithms. Each algorithm operates

independently and controls a separate fan driver. Each algorithm is controlled manually (by setting the

target fan speed).

This fan control algorithm uses Proportional, Integral, and Derivative terms to automatically approach

and maintain the system’s desired fan speed to an accuracy directly proportional to the accuracy of

the clock source.

The desired tachometer count is set by the user inputting the desired number of 32.768kHz cycles that

occur per fan revolution. This is done by manually setting the TACH Target Register. The user may

change the target count at any time. The user may also set the target count to FFh in order to disable

the fan driver for lower current operation.

For example, if a desired RPM rate for a 2-pole fan is 3000 RPMs, then the user would input the

hexidecimal equivalent of 1296 (51h in the TACH Target Register). This number represents the number

of 32.768KHz cycles that would occur during the time it takes the fan to complete a single revolution

when it is spinning at 3000RPMs.

Table 4.1 Fan Controls Active for Operating Mode

DIRECT SETTING MODE

FSC MODE

Fan Driver Setting (read / write)

Fan Driver Setting (read only)

EDGES[1:0]

(Fan Configuration)

RANGE[1:0]

(Fan Configuration)

UPDATE[2:0]

(Fan Configuration)

UPDATE[2:0]

(Fan Configuration)

LEVEL

(Spin Up Configuration)

LEVEL

(Spin Up Configuration)

SPINUP_TIME[1:0]

(Spin Up Configuration)

SPINUP_TIME[1:0]

(Spin Up Configuration)

Fan Step

Fan Minimum Drive

Valid TACH Count

TACH Target (read / write)

TACH Reading

DRIVE_FAIL_CNT[1:0] and Drive Band Fail Registers

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