THMC10

REMOTE/LOCAL TEMPERATURE MONITOR

WITH SMBus INTERFACE

SLIS089 – DECEMBER 1999

15

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

PC board layout checklist (continued)

10 MILS

DXN

DXP

GND

GND

10 MILS

MINIMUM

10 MILS

10 MILS

Figure 7. Recommended PC Board Layout for DXP/DXN Traces

uses of twisted pair and shielded cables

For remote-sensor distances longer than 8 inches or in particularly noisy environments, a twisted pair is

recommended. Its practical length is 6 feet to 12 feet (typical) before noise becomes a problem, as tested in

a noisy electronics laboratory. For longer distances, the best solution is a shielded twisted pair like that used

for audio microphones. For example, a Belden

® #8451 works well for distances up to 100 feet in a noisy

environment. Connect the twisted pair to DXP and DXN and the shield to GND, and leave the shield’s remote

end unterminated. Excess capacitance at DXN limits practical remote sensor distances (see A/D and supply

dc electrical characteristics). For very long cable runs, the cable’s parasitic capacitance often provides noise

filtering; hence, the 2200-pF capacitor can often be removed or reduced in value. Cable resistance also affects

remote-sensor accuracy. A 1-

Ω series resistance introduces about 0.5°C error.

Belden is a registered trademark of Belden Corporation.