TMP411 datasheet(33/48 Pages) TI2

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Ambient Temperature, TA ( °C)

3.0

2.0

1.0

í1.0

í2.0

í3.0

í50

125

í25

100

50 Units Shown

S = 3.3V

í1

í2

í3

í50

í25

125

100

S = 3.3V

DIODE = +25 °C (temperature at remote diode)

30 Typical Units Shown

= 1.008

Ambient Temp erature,

(°C)

TMP411

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SBOS383D – DECEMBER 2006 – REVISED DECEMBER 2016

Product Folder Links: TMP411

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Typical Application (continued)

Based on these criteria, TI recommends using two small-signal transistors, such as the 2N3904 (NPN) or

2N3906 (PNP).

10.2.2 Detailed Design Procedure

The temperature measurement accuracy of the TMP411 depends on the remote or local temperature sensor

being at the same temperature as the monitored system point. If the temperature sensor is not in good thermal

contact with the part of the system being monitored, then there is a delay in the response of the sensor to a

temperature change in the system. For remote temperature sensing applications using a substrate transistor (or

a small, SOT-23 transistor) placed close to the device , this delay is usually not a concern.

The local temperature sensor inside the TMP411 monitors the ambient air around the device. The thermal time

constant for the TMP411 is approximately two seconds. This constant implies that if the ambient air changes

quickly by 100°C, the TMP411 takes approximately 10 seconds (that is, five thermal time constants) to settle

within 1°C of the final value. In most applications, the TMP411 package is in electrical (and thermal contact) with

the printed circuit board (PCB), and subjected to forced airflow. The accuracy of the temperature measurement

directly depends on how accurately the PCB and forced airflow temperatures represent the temperature

measured by the device. Additionally, the internal power dissipation of the TMP411 can cause the temperature to

rise above the ambient or PCB temperature. The internal power dissipated is a result of exciting the remote

temperature sensor is negligible because of the small currents used.

For a 3.3-V supply and maximum conversion rate of eight conversions per second, the TMP411 dissipates 1.32

mW (PD IQ = 3.3 V × 400 µA). If the ALERT/THERM2 and THERM pins are each sinking 1 mA, an additional

power of 0.8 mW is dissipated (PD OUT = 1 mA × 0.4 V + 1 mA × 0.4 V = 0.8 mW). Total power dissipation

equals 2.12 mW (PD IQ + PD OUT) and (with a θJA value of 150°C/W) causes the junction temperature to rise

approximately 0.318°C above the ambient.

10.2.3 Application Curves

Figure 19. Remote Temperature Error vs TMP411 Ambient

Temperature

Figure 20. Local Temperature Error vs TMP411 Ambient

Temperature

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