Remote temperature sensing on the TMP9R01-SEP and TMP9R01-SP devices measure very small voltages using very low currents; therefore, noise at the device inputs must be minimized. Most applications using the device have high digital content, with several clocks and logic-level transitions that create a noisy environment. Layout must adhere to the following guidelines:
- Place the TMP9R01-SEP and TMP9R01-SP devices as close to the remote junction sensor as possible.
- 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 9-4. If a multilayer PCB is used, bury these traces between the ground or V+ planes to shield them from extrinsic noise sources. 5mil (0.127mm) PCB traces are recommended.
- 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.
- Use a 0.1μF local bypass capacitor directly between the V+ and GND of the device. For optimum measurement performance, minimize filter capacitance between D+ and D– to 1000pF or less. This capacitance includes any cable capacitance between the remote temperature sensor and the device.
- If the connection between the remote temperature sensor and the device is less than 8in (20.32cm) 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 device as possible. Leave the remote sensor connection end of the shield wire open to avoid ground loops and 60Hz pickup.
- Thoroughly clean and remove all flux residue in and around the pins of the TMP9R01-SEP and TMP9R01-SP devices to avoid temperature offset readings as a result of leakage paths between D+ and GND, or between D+ and V+.