SMBus Fan Control with 1°C Accurate Temperature Monitoring
Datasheet
EMC2101-R
EEPROM
or Host
SMCLK
SMBus
Client
SMDATA
EEPROM
Loader
GPU
DP
Thermal
ALERT
DN
Internal
Diode
diode
FAN
Fan Drive
Circuitry
Figure 5.2 System Diagram for EMC2101-R
5.1
Modes of Operation (EMC2101-R Only)
The EMC2101-R has two modes of operation based on the pull-up resistor on the ALERT pin (see
Table 5.1). The modes of operation are:
1. Host Configuration Mode - An SMBus Host configures the EMC2101-R upon startup to allow for
polling for temperature or fan information or the user can use the ALERT pin interrupt to determine
which action is required.
2. Automatic Configuration Mode - The EMC2101-R queries an SMBus compatible EEPROM located
at a known address (see Section 4.9) and automatically loads its registers with the contents of the
EEPROM. This mode does not require host intervention but a host can poll the device for
temperature and fan information.
5.2
5.3
Power Up (EMC2101-R Only)
The EMC2101-R (only) will power up with the fan driver set to either 100% duty cycle or 0% duty cycle,
depending on the value of the pull-up resistor on the ALERT / TACH pin. (See Table 5.1.) It will remain
in this state until either the Fan Setting Register is written or until the following activities have occurred:
1. The Fan Control Look-Up Table is loaded and the PROG bit is set to ‘0’
2. The temperature monitoring block performs its first comparison against the Look-Up Table.
If the Fan Control Look-Up Table is used, the EMC2101-R Fan Driver will be immediately set to the
appropriate setting in the table based on the measured temperature.
Power Modes
The EMC2101 supports multiple power modes that are user configurable. The temperature monitoring
and fan control functions of the device are independent. The power modes are:
1. Normal - the temperature monitoring and fan driver circuits are both active. The device updates all
temperature channels at the user programmed conversion rate (see Table 6.6). Every time the
temperature is updated, the limits are checked and the fan driver is updated based on the values
in the Fan Control Look-Up Table (if the Fan Control Look-Up Table is enabled).
2. Standby - the temperature monitoring and fan driver circuits are both disabled. The device will not
update temperature data automatically and the fan output will be set to default drive. A one-shot
SMSC EMC2101
Revision 2.53 (03-13-07)
DATA1S9HEET
SMSC [ SMSC CORPORATION ]
