1°C Triple SMBus Temperature Sensor

Datasheet

Revision 2.3 (04-19-05)

6

SMSC EMCT03

DATASHEET

Chapter 3 Product Description

The EMCT03 is an SMBus sensor that is capable of monitoring three temperature zones. The part

may be used as a companion to one of SMSC’s broad line of SIO host circuits, or other devices

capable of performing the SMBus host function.

Figure 3.1 System Overview

In cooperation with the host device, thermal management can be performed as outlined in Figure 3.1

above. Thermal management consists of the host reading the temperature data from the remote and

internal temperature diodes of the EMCT03 and controlling the speed of one or multiple fans. Since

the EMCT03 incorporates one internal and two external temperature diodes, three separate thermal

zones can be monitored and controlled with this application. Also, measured temperature levels can

quickly be compared to preset limits within the host device which in turn will take the appropriate action

when values are found to be out of limit.

The EMCT03 has two basic modes of operation:

■

Run Mode: In this mode, the EMCT03 continuously converts temperature data and updates its

registers. The conversion rate is configured by the lower bits in the configuration register as

described in Table 3.11, "Configuration Register, Conversion Rate," on page 11.

■

Standby Mode: In this mode, the EMCT03 is powered down, drawing a maximum current of only

3uA. The SMBus is still operational and a one-shot command can be given which will force the

circuit to complete one full set of temperature conversions. The EMCT03 will return to Standby

Mode after the one shot conversion has finished.

3.1

Temperature Monitors

Thermal diode temperature measurements are based on the change in forward bias voltage of a diode

when operated at two different currents:

where:

K is Boltzmann’s constant

T is Absolute Temperature in Kelvin

q is Charge Electron

n is Diode Ideality factor

The change in forward bias voltage is now proportional to absolute temperature T.

EMCT03

Host

(SMSC SIO)

SMBus

Interface

DP1

DN1

SMBus

Internal

Diode

DP2

DN2













=

−

low

high

low

be

high

be

I

I

q

KT

n

V

V

ln

_

_

(1)