V+

D+

D-

GND

Ground or V+ layer

on bottom and top,

if possible.

27

TMP461

www.ti.com

SBOS722B – JUNE 2015 – REVISED AUGUST 2016

Product Folder Links: TMP461

Submit Documentation Feedback

Copyright © 2015–2016, Texas Instruments Incorporated

11 Layout

11.1 Layout Guidelines

Remote temperature sensing on the TMP461 device measures very small voltages using very low currents;

therefore, noise at the device inputs must be minimized. Most applications using the TMP461 have high digital

content, with several clocks and logic-level transitions that create a noisy environment. Layout must adhere to

the following guidelines:

1. Place the TMP461 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 21. 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 TMP461 device. 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 TMP461

device.

5. If the connection between the remote temperature sensor and the TMP461 device is less than 8-in

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

pair with the shield grounded as close to the TMP461 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 TMP461 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 21. Suggested PCB Layer Cross-Section