Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The TMP175-Q1 and TMP75-Q1 devices are used to measure the printed circuit board (PCB) temperature of where the device is mounted. The TMP175-Q1 and TMP75-Q1 feature SMBus, two-wire, and I2C interface compatibility, with the TMP175-Q1 allowing up to 27 devices on one bus and the TMP75-Q1 allowing up to eight devices on one bus. The TMP175-Q1 and TMP75-Q1 both feature a SMBus Alert function. The TMP175-Q1 and TMP75-Q1 require no external components for operation except for pullup resistors on SCL, SDA, and ALERT, although a 0.1-μF bypass capacitor is recommended.
The sensing device of the TMP175-Q1 and TMP75-Q1 devices is the device itself. Thermal paths run through the package leads as well as the plastic package. The lower thermal resistance of metal causes the leads to provide the primary thermal path.
The TMP175-Q1 and TMP75-Q1 devices requires pullup resistors on the SCL, SDA, and ALERT pins. The recommended value for the pullup resistor is 5 kΩ. In some applications the pullup resistor can be lower or higher than 5 kΩ, but must not exceed 3 mA of current on the SCL and SDA pins and must not exceed 4 mA on the ALERT pin. A 0.1-μF bypass capacitor is recommended, as shown in Figure 13. The SCL, SDA, and ALERT lines can be pulled up to a supply that is equal to or higher than VS through the pullup resistors. For the TMP175-Q1, to configure one of 27 different addresses on the bus, connect A0, A1, and A2 to either the GND or the V+ pin or float these pins. Float indicates that the pin is left unconnected. For the TMP75-Q1, to configure one of eight different addresses on the bus, connect A0, A1, and A2 to either the GND or V+ pin.
Place the TMP175-Q1 and TMP75-Q1 devices in close proximity to the heat source that must be monitored, with a proper layout for good thermal coupling. This placement ensures that temperature changes are captured within the shortest possible time interval. To maintain accuracy in applications that require air or surface temperature measurement, take care to isolate the package and leads from ambient air temperature. A thermally-conductive adhesive is helpful in achieving accurate surface temperature measurement.
Figure 14 shows the step response of the TMP175-Q1 and TMP75-Q1 devices to a submersion in an oil bath of 100ºC from room temperature (27ºC). The time-constant, or the time for the output to reach 63% of the input step, is 1.5 s. The time-constant result depends on the PCB where the TMPx175 devices are mounted. For this test, the TMP175-Q1 and TMP75-Q1 devices were soldered to a two-layer PCB that measured 0.375 inches × 0.437 inches.