Dual RPM-Based PWM Fan Controller
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.
3.3V
VDD
tachometer
TACH2
PWM2
SMCLK
SMDATA
ALERT#
MCU
Drive
Circuit
32.768KHz Clock
Input or Output
CLK
EMC2302
tachometer
TACH1
PWM1
GND
Drive
Circuit
Figure 4.1 System Diagram of 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.
Revision 1.1 (10-12-09)
SMSC EMC2302
DATA1S6HEET
SMSC [ SMSC CORPORATION ]
