TMP468 datasheet(34/43 Pages) TI1

34 / 43 page

V+

D+

D-

GND

Ground or V+ layer

on bottom and top,

if possible.

TMP468

SBOS762 – NOVEMBER 2016

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11 Layout

11.1 Layout Guidelines

Remote temperature sensing on the TMP468 device measures very small voltages using very low currents;

therefore, noise at the device inputs must be minimized. Most applications using the TMP468 have high digital

content, with several clocks and a multitude of logic-level transitions that create a noisy environment. Layout

must adhere to the following guidelines:

1. Place the TMP468 device as close to the remote junction sensor as possible.

2. 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 26. If a multilayer PCB is used, bury these traces between the

ground or V+ planes to shield them from extrinsic noise sources. 5-mil (0.127 mm) PCB traces are

recommended.

3. 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.

4. Use a 0.1-μF local bypass capacitor directly between the V+ and GND of the TMP468. For optimum

measurement performance, minimize filter capacitance between D+ and D– to 1000 pF or less. This

capacitance includes any cable capacitance between the remote temperature sensor and the TMP468.

5. If the connection between the remote temperature sensor and the TMP468 is wired and is less than 8-in

(20.32 cm) long, use a twisted-wire pair connection. For lengths greater than 8 inches, use a twisted,

shielded pair with the shield grounded as close to the TMP468 device as possible. Leave the remote sensor

connection end of the shield wire open to avoid ground loops and 60-Hz pickup.

6. Thoroughly clean and remove all flux residue in and around the pins of the TMP468 to avoid temperature

offset readings as a result of leakage paths between D+ and GND, or between D+ and V+.

NOTE: Use a minimum of 5-mil (0.127 mm) traces with 5-mil spacing.

Figure 26. Suggested PCB Layer Cross-Section

TMP468 Datasheet(PDF) 34 Page - Texas Instruments