SMBus Fan Control with 1°C Accurate Temperature Monitoring
Datasheet
Chapter 5 General Description
The EMC2101 is an environmental monitoring device with a selectable PWM or DAC fan driver output,
one external temperature monitoring channel and one internal temperature monitor. It contains
advanced circuitry to remove errors induced by series resistance and CPU thermal diode process
differences to provide accurate temperature measurements and accurate fan control.
Thermal management is performed automatically. The EMC2101 reads the temperature from both the
external and internal temperature diodes and uses the external temperature data to control the fan
speed.
The FAN output can be configured as a PWM (default) or DAC output. The PWM fan driver uses an
eight entry look up table to create a programmable temperature response. The DAC output provides
a linear drive for the system fan circuit using this same look up table.
Each temperature measurement channel is continuously compared against programmed high limits.
The external diode channel is compared against a programmed low limit. ALERT / TACH interrupt pin
is asserted if the measured value exceeds the high limit or drops below the low limit. In addition, the
external diode contains a programmable critical temperature, TCRIT. If the measured temperature
exceeds this TCRIT an interrupt is asserted on the ALERT / TACH pin and the fan is set to full on.
Finally, the EMC2101-R (only) has two configuration modes and two default fan settings based on the
value of the pull-up-resistor on the ALERT / TACH pin. In the Manual Configuration Mode, the device
acts as an SMBus client and waits to be configured by the system SMBus host. In the Automatic
Configuration mode, the device automatically queries the SMBus for an EEPROM device and uploads
configuration information from the EEPROM into its internal registers.
Figure 5.1 shows a system level block diagram of the EMC2101. Figure 5.2 shows a system level block
diagram of the EMC2101-R.
HOST
EMC2101
DP
DN
Thermal
diode
SMCLK
SMDATA
Internal
Diode
SMBus
Interface
ALERT
FAN
Fan Drive
Circuitry
Figure 5.1 System Diagram for EMC2101
Revision 2.53 (03-13-07)
SMSC EMC2101
DATA1S8HEET
SMSC [ SMSC CORPORATION ]
