EMC2302 datasheet(16/44 Pages) SMSC

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Dual RPM-Based PWM Fan Controller

Datasheet

Revision 1.1 (10-12-09)

SMSC EMC2302

DATASHEET

Chapter 4 Product Description

The EMC2302 is an SMBus compliant fan controller with two programmable frequency PWM fan

drivers. The fan drivers can be operated using two modes: the RPM-based Fan Speed Control

Algorithm or the direct fan drive setting.

Figure 4.1 shows a system diagram of the EMC2302.

4.1

Fan Control Modes of Operation

The EMC2302 has two modes of operation for each fan driver. Each mode of operation uses the Ramp

Rate control and Spin Up Routine.

1. Direct Setting Mode - in this mode of operation, the user directly controls the fan drive setting.

Updating the Fan Driver Setting Register (see Section 5.7) will instantly update the PWM fan drive.

Ramp Rate control is optional and enabled via the EN_RRC bits.

Whenever the Direct Setting Mode is enabled, the current drive will be changed to what was

last written into the Fan Driver Setting Register.

2. Fan Speed Control Mode (FSC) - in this mode of operation, the user determines a target

tachometer count and the PWM drive setting is automatically updated to achieve this target speed.

The algorithm uses the Spin Up Routine and has user definable ramp rate controls.

This mode is enabled setting the EN_ALGO bit in the Fan Configuration Register.

Figure 4.1 System Diagram of EMC2302

EMC2302

SMCLK

SMDATA

ALERT#

VDD

3.3V

MCU

TACH1

tachometer

PWM1

Drive

Circuit

TACH2

tachometer

PWM2

Drive

Circuit

32.768KHz Clock

Input or Output

CLK

GND

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