THMC10 datasheet(14/20 Pages) TI

14 / 20 page

THMC10

REMOTE/LOCAL TEMPERATURE MONITOR

WITH SMBus INTERFACE

SLIS089 – DECEMBER 1999

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

PC board layout considerations

D Place the THMC10 as close as practical to the remote diode. In a noisy environment, such as a computer

motherboard, this distance can be 4 inches to 8 inches (typical) or more, as long as the worst noise sources

(such as CRTs, clock generators, memory buses, and ISA/PCI buses) are avoided.

D Route the DXP–DXN lines away from the deflection coils of a CRT. Also, avoid routing the traces across

a fast memory bus which can easily introduce 30

°C error even with good filtering. Otherwise, most noise

sources are fairly benign.

D Route the DXP and DXN traces in parallel and in close proximity to each other, away from any high-voltage

traces such as 12 Vdc. Leakage currents from PC board contamination must be be taken into consideration,

since a 20-M

Ω leakage path from DXP to ground causes about 1°C error.

D Connect guard traces to GND on either side of the DXP–DXN traces (Figure 7). With guard traces in place,

routing near high-voltage traces is not an issue.

D Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects.

D When introducing a thermocouple, insure that both the DXP and the DXN paths have matching

thermocouples. In general, PC board induced thermocouples are not a serious problem. A copper-solder

thermocouple exhibits 3

µV/°C, and it takes about 200 µV of voltage error at DXP–DXN to cause a 1°C

measurement error. Hence, most parasitic thermocouple errors are swamped out.

D Use wide traces. Narrow traces are more inductive and tend to pick up radiated noise. The 10-mil widths

and spacings recommended in Figure 7 are not absolutely necessary as they offer only a minor

improvement in leakage and noise, but usage is recommended where practical.

D Copper can not be used as an EMI shield and only ferrous materials such as steel work well. Placing a

copper ground plane between the DXP–DXN traces and traces carrying high-frequency noise signals does

not help reduce EMI.

PC board layout checklist

D Place the THMC10 as close as possible to the remote diode.

D Keep traces away from high voltages (12 V bus).

D Keep traces away from fast data/memory buses and CRTs.

D Use recommended trace widths and spacings.

D Place a ground plane under the traces.

D Use guard traces flanking DXP and DXN and connecting to GND.

D Place the noise filter and the 0.1-µF VDD bypass capacitors close to the THMC10.

THMC10 датащи(PDF) 14 Page - Texas Instruments