9.2.1.2.1 Voltage Drop Effect

Take into account the voltage drop that occurs along the supply and ground lines as a result of the currents of all the devices on the line. This voltage drop occurs as a result of multiple devices simultaneously consuming current through the combined resistance of the common wire, connectors, and solder contacts. Make sure that the supply on the last device does not fall below the minimum operating supply of 1.7 V during any mode of operation, or below 1.8 V during EEPROM programming and chain initialization.

9.2.1.2.2 EEPROM Programming Current

Another parameter to consider is the EEPROM programming current. The device consumes higher current during EEPROM programming than during regular operation, as specified in the Electrical Characteristics section. This higher current consumption results in a larger voltage drop along the supply and ground lines and may lead to similar issues as mentioned previously. To avoid large, simultaneous, programming currents from multiple devices, program the EEPROM on the devices using the individual write commands instead of the global write commands.

9.2.1.2.3 Power Savings

In continuous-conversion mode, the TMP107-Q1 continuously measures temperature and consumes the most power out of any of the operating modes. For maximum power savings, place the TMP107-Q1 in shutdown mode. In shutdown mode, the TMP107-Q1 shuts down all internal active circuitry except for the required circuit elements that allow communication with the device. Issue a one-shot command when in shutdown mode to trigger a single temperature measurement.

9.2.1.2.4 Accuracy

In order to achieve the best temperature accuracy when multiple devices are connected in the daisy-chain, configure the devices in shutdown mode, and then issue a one-shot conversion. Read the temperature from all devices on the bus by issuing a global read after a delay of 20 ms. This delay after the one-shot command makes sure the internal ADC conversion is finished, and the voltages of the supply bypass capacitors over the daisy chain are stable, before the data are read by the host.

9.2.1.2.5 Electromagnetic Interference (EMI)

The typical, three-conductor TMP107-Q1 measurement chain is fairly insensitive to electromagnetic distortions because the supply, ground and signal wires are running in parallel and located in the same cable housing. To help maintain this insensitivity, do not make any additional electric connections at intermediate nodes in the cable, or at the end of the chain of TMP107-Q1 devices.

There can be environmental effects on a TMP107-Q1 cable implementation in the form of conducted emission. The conducted susceptibility of the cable can be investigated if this is a suspected source of interference. Designing for electromagnetic compatibility with the intended operating environment can mitigate interference. There can be radiated emission from the TMP107-Q1 cable implementation that may affect the radiated susceptibility of surrounding equipment. See specification IEC61000-4-3: Testing and measurement techniques - Radiated, radio-frequency, electromagnetic field immunity test for more information on testing for radiated immunity to signals in the 80-MHz to 6-GHz range. Also, see IEC61000-4-6: Testing and measurement techniques - Immunity to conducted disturbances, induced by radio-frequency fields for information on testing for conducted immunity in the 9-kHz to 80-MHz range.

Physical shielding and electrical filtering can mitigate much of the interference into and out of the surrounding environment and electronics. See IEC62153-4-X: Metallic Communication Cable Test Methods for information on determining the screening effectiveness of a metallic cable shield. The thermal conductivity of additional material around the cable implementation can affect the settling time of the TMP107-Q1 at its position in the cable. This thermal conductivity can also reduce the allowable temperature range exposure of the cable implementation depending on the materials chosen. Generally, passive electrical filtering is very effective at suppressing conducted interference. Circuit board components, such as an EMI filter that increases in resistance significantly in response to higher frequency content, are widely available and often easy to implement. Even simple RC and LC filter configurations on transmission lines provide some immunity.