RPM-Based PWM Fan Controller
Datasheet
Chapter 4 Product Description
The EMC2301 is an SMBus compliant fan controller with a programmable frequency PWM fan driver.
The fan driver 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 EMC2301.
3.3V
VDD
tachometer
TACH
PWM
SMCLK
SMDATA
ALERT#
MCU
Drive
Circuit
32.768KHz Clock
Input or Output
GND
CLK
EMC2301
Figure 4.1 System Diagram of EMC2301
4.1
Fan Control Modes of Operation
The EMC2301 has two modes of operation for the 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.
Table 4.1 Fan Controls Active for Operating Mode
DIRECT SETTING MODE
FSC MODE
Fan Driver Setting (read only)
Fan Driver Setting (read / write)
EDGES[1:0]
EDGES[1:0]
(Fan Configuration)
Revision 1.1 (10-12-09)
SMSC EMC2301
DATA1S6HEET
SMSC [ SMSC CORPORATION ]
