Datasheet

Revision 1.1 (06-11-08)

8

SMSC EMC1203/EMC1204

DATASHEET

either be a CPU substrate diode or a regular thermal diode-connected transistor. External diodes at

DP2/DN3 and DN2/DP3 have to be connected in an anti-parallel fashion. Because of this, one diode

will be forward biased while the other is reverse biased and therefore it is recommended to connect

only discrete thermal diodes to these pins.

Do not use the anti-parallel interface (DP2/DN3 and DN2/DP3) to connect substrate transistors

(sometimes called thermal diodes or on-chip sense junctions). External diode connected transistors

examples are shown in Figure 3.4

Figure 3.4 EMC1204 External Diode Examples

3.2

SMSC BudgetBus™ Sensor Interface

The EMC1203 and EMC1204 series of temperature monitors communicate with a host controller, such

as the KBC1100, through the SMSC BudgetBus™ Sensor Interface. The BBUS is a single wire serial

communication protocol between the computer host and its peripheral devices. Please refer to the

SMSC BudgetBus™ Sensor Interface Specification for detailed information about the modes of

operation.

3.3

Power Modes

The EMC1203 and EMC1204 have two basic modes of operation:

Standby Mode:

The host can initiate standby mode by actively pulling the BBUS low. When the Host places the device

in standby mode, the device immediately powers down to draw < 2uA of supply current. It will remain

in this state until it is awakened by the host. If the host pulls the BBUS line low while temperature data

is being clocked out, the device will not enter standby mode until completion of the data transfer. After

entering standby mode, the device will remain in this mode until it is forced into active mode by the

host. The transition from standby to active mode occurs when the host is no longer pulling the BBUS

low.

Active Mode:

The host initiates active mode by enabling a weak pull up on the BBUS. In this mode, the EMC1203

and EMC1204 continuously convert temperature data. During the time that the device is actively

converting a temperature, the BBUS is in tri-state mode, and the Host places a weak pull-up on the

bus to prevent it from floating. After a conversion is completed, the device automatically clocks out the

data from the most recent conversion to the host. When the data packet has been entirely clocked out,

the BBUS returns to tri-state mode, and the ADC begins converting the next temperature sample.

While BBUS is in tri-state mode, the host can command the device to standby mode.

Typical remote

discrete PNP transistor

i.e. 2N3906

Typical remote

discrete NPN transistor

i.e. 2N3904

to DP2/DN3

to DN2/DP3

to DP2/DN3

to DN2/DP3