TMP442 datasheet(22/29 Pages) TI1

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LAYOUT CONSIDERATIONS

V+

DXP

DXN

GND

NOTE:Useminimum5miltraceswith5milspacing.

GroundorV+layer

onbottomand/or

top,ifpossible.

TMP441

0.1mFCapacitor

V+

GND

PCBVia

DXP

DXN

TMP442

0.1mFCapacitor

V+

GND

PCBVia

DXP1

DXN1

DXP2

DXN2

TMP441

TMP442

SBOS425A – DECEMBER 2008 – REVISED MARCH 2009 .............................................................................................................................................. www.ti.com

Remote temperature sensing on the TMP441/42

measures

very

small

voltages

using

very

low

currents; therefore, noise at the IC inputs must be

minimized. Most applications using the TMP441/42

will have high digital content, with several clocks and

logic level transitions creating a noisy environment.

Layout should adhere to the following guidelines:

1. Place the TMP441/42 as close to the remote

junction sensor as possible.

2. Route the DXP and DXN 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

(0.005

in,

0,127

mm)

PCB

traces

are

recommended.

3. Minimize

additional

thermocouple

junctions

Figure 19. Suggested PCB Layer Cross-Section

caused by copper-to-solder connections. If these

junctions are used, make the same number and

approximate

locations

copper-to-solder

connections

both

the

DXP

and

DXN

connections to cancel any thermocouple effects.

4. Use a 0.1

µF local bypass capacitor directly

between the V+ and GND of the TMP441/42, as

shown in Figure 20. Minimize filter capacitance

between DXP and DXN to 330pF or less for

optimum

measurement

performance.

This

capacitance

includes

any

cable

capacitance

between the remote temperature sensor and

TMP441/42.

5. If

the

connection

between

the

remote

temperature sensor and the TMP441/42 is less

than 8 in (20,32 cm) long, use a twisted-wire pair

connection. Beyond 8 in, use a twisted, shielded

pair with the shield grounded as close to the

TMP441/42 as possible. Leave the remote sensor

connection end of the shield wire open to avoid

ground loops and 60Hz pickup.

6. Thoroughly clean and remove all flux residue in

and around the pins of the TMP441/42 to avoid

temperature offset readings as a result of leakage

paths between DXP or DXN and GND, or

between DXP or DXN and V+.

Figure 20. Suggested Bypass Capacitor

Placement and Trace Shielding

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