BBUS Compliant Dual Temperature Monitor with Beta Compensation

Datasheet

SMSC EMC1212

7

Revision 1.1 (02-07-07)

DATASHEET

Chapter 3 Product Description

The EMC1212 is a SOT23 temperature sensor with a proprietary single wire SMSC BudgetBus™

Sensor Interface. Temperature information is communicated to a host device via the serial bus. All

intelligence regarding the interpretation of temperature resides in the host. The EMC1212 monitors an

internal diode and single external transistor and automatically corrects for errors induced by series

resistance and beta variation. Figure 3.1 shows a typical system overview:

Thermal management consists of the host acquiring the temperature data from the EMC1212 and

controlling the speed of one or more fans. Because the EMC1212 incorporates one internal and one

external temperature diode, up to two separate thermal zones can be monitored and controlled. The

host has the ability to compare measured temperature levels to preset limits and take the appropriate

action when values are found to be out of limit.

3.1

Power Modes

The EMC1212 has two basic modes of operation that are controlled entirely by the host device.

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 EMC1212

continuously converts 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.

Figure 3.1 System Diagram of EMC1212

EMC1212

Host

(e.g. KBC1122)

BBUS

Interface

DP

DN

BBUS