1°C Triple SMBus Temperature Sensor

Datasheet

Revision 2.3 (04-19-05)

14

SMSC EMCT03

DATASHEET

Figure 4.1 Routing the Diode Traces

4.1.1.2

Bypass Capacitors

Accurate temperature measurements require a clean, stable power supply. Locate a 0.1µF capacitor

as close as possible to the power pin with a good ground. A low ESR capacitor (such as a 10µF

ceramic) should be placed across the power source. Add additional power supply filtering in systems

that have a noisy power supply.

A capacitor may be placed across the DP/DN pair at the remote sensor in noisy environments. Do not

exceed a value of 100 pF if this capacitor is installed.

4.1.1.3

Manufacturing

Circuit board assembly processes may leave a residue on the board. This residue can result in

unexpected leakage currents that may introduce errors if the circuit board is not clean. For example,

processes that use water-soluble soldering fluxes have been known to cause problems if the board is

not kept clean.

4.1.1.4

Thermal Considerations

Keep the sensor in good thermal contact with the component to be measured. The temperature of the

leads of a discrete diode will greatly impact the temperature of the diode junction. Make use of the

printed circuit board to disperse any self-heating that may occur.

4.1.1.5

Remote Sensors Connected by Cables

When connecting remote diodes with a cable (instead of traces on the PCB) use shielded twisted pair

cable. The shield should be attached to ground near the EMCT03, and should be left unconnected at

the sensor end. Belden 8451 cable is a good choice for this application.

4.1.2

Sensor Characteristics

The characteristics of the diode junction used for temperature sensing will affect the accuracy of the

measurement.

4.1.2.1

Selecting a Sensor

A diode connected small signal transistor is recommended. Silicon diodes are not a good choice for

remote sensors. Small signal transistors such as the 2N3904 or the 2N3906 are recommended.

Desired characteristics for the sensor include the following:

another or one manufacturer to another cancels out of the temperature equations.

COPPER TRACE

COPPER TRACE

.01 WIDE MIN.

.01 GAP MIN.

.01 WIDE MIN.

GND PLANE

.01 GAP MIN.

GND PLANE

.01 GAP MIN.

COPPER PLANE (TO SHIELD FROM NOISE)

BOARD MATERIAL

RECOMMEND VIA STICTCHING AT .25 INCH INTERVALS.

DP or DN

DP or DN