1°C Dual SMBus Sensor with Resistance Error Correction

Datasheet

SMSC EMC1002

19

Revision 1.3 (03-24-06)

DATASHEET

5.1.1.2

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 2.2nF if this capacitor is installed.

5.1.1.3

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.

5.1.1.4

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.

5.1.1.5

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 EMC1002, and should be left unconnected

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

5.1.2

Sensor Characteristics

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

measurement.

5.1.2.1

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. Select

equations.

5.1.2.2

Compensating for Ideality of the diode

The remote diode may have an ideality factor based on the manufacturing process. Inaccuracy in the

temperature measurement resulting from this ideality factor may be eliminated by configuring the

ideality factor register. The EMC1002 is trimmed to an ideality factor of 1.008.

5.1.2.3

Circuit Connections

The more negative terminal for the remote temperature diode, DN, is internally biased with a forward

diode voltage. Terminal DN is not referenced to ground. Remote temperature diodes can be

constructed as shown in Figure 5.2 Remote Temperature Diode Examples on page 20.