TMP411CD datasheet(23/32 Pages) TI

23 / 32 page

TMP411

SBOS383C − DECEMBER 2006 − REVISED MAY 2008

www.ti.com

LAYOUT CONSIDERATIONS

Remote temperature sensing on the TMP411 measures

very small voltages using very low currents; therefore,

noise at the IC inputs must be minimized. Most

applications using the TMP411 will have high digital

content, with several clocks and logic level transitions

creating a noisy environment. Layout should adhere to the

following guidelines:

Place the TMP411 as close to the remote junction

sensor as possible.

Route the D+ and D− traces next to each other and

shield them from adjacent signals through the use of

ground guard traces, as shown in Figure 19. If a

multilayer PCB is used, bury these traces between

ground or VDD planes to shield them from extrinsic

noise sources. 5 mil PCB traces are recommended.

Minimize additional thermocouple junctions caused

by copper-to-solder connections. If these junctions

are used, make the same number and approximate

locations of copper-to-solder connections in both the

D+ and D− connections to cancel any thermocouple

effects.

Use a 0.1

µF local bypass capacitor directly between

the V+ and GND of the TMP411, as shown in

Figure 20. Minimize filter capacitance between D+

and D− to 1000pF or less for optimum measurement

performance. This capacitance includes any cable

capacitance between the remote temperature sensor

and TMP411.

If the connection between the remote temperature

sensor and the TMP411 is less than 8 inches, use a

twisted-wire pair connection. Beyond 8 inches, use a

twisted, shielded pair with the shield grounded as

close to the TMP411 as possible. Leave the remote

sensor connection end of the shield wire open to avoid

ground loops and 60Hz pickup.

GND(1)

D+(1)

−(1)

GND(1)

NOTE: (1) 5 mil traces with 5 mil spacing.

Ground or V+ layer

on bottom and/or

top, if possible.

Figure 19. Example Signal Traces

TMP411

0.1

µF Capacitor

PCB Via

V+

GND

Figure 20. Suggested Bypass Capacitor

Placement

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