11.1 Layout Guidelines

Remote temperature sensing on the TMP43x measures very small voltages using very low currents; therefore, noise at the IC inputs must be minimized. Most applications using the TMP43x have high digital content, with several clocks and logic level transitions creating a noisy environment. Layout must conform to the following guidelines:

1. Place the TMP43x 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; see Figure 25. If a multilayer PCB is used, bury these traces between ground or V_DD 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 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 TMP43x. Figure 26 illustrates the suggested bypass capacitor placement for the TMP43x. This capacitance includes any cable capacitance between the remote temperature sensor and TMP43x.
5. If the connection between the remote temperature sensor and the TMP43x is less than 8 inches
   (20.32 cm), use a twisted-wire pair connection. Beyond 8 inches, use a twisted, shielded pair with the shield grounded as close to the TMP43x 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 TMP43x to avoid temperature offset readings as a result of leakage paths between DXP or DXN and GND, or between DXP or DXN and V+.