TMP464 datasheet(32/43 Pages) TI1

32 / 43 page

V+

D+

D-

GND

Ground or V+ layer

on bottom and top,

if possible.

TMP464

SBOS835 – MAY 2017

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10 Layout

10.1 Layout Guidelines

Remote temperature sensing on the TMP464 device measures very small voltages using very low currents;

therefore, noise at the device inputs must be minimized. Most applications using the TMP464 device 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 TMP464 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 23. If a multilayer PCB is used, bury these traces between the

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

traces.

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 TMP464. 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 TMP464.

5. If the connection between the remote temperature sensor and the TMP464 is wired and is less than eight

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

twisted, shielded pair with the shield grounded as close to the TMP464 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 TMP464 device 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 23. Suggested PCB Layer Cross-Section

TMP464 Datasheet(PDF) 32 Page - Texas Instruments