TMP411 datasheet(42/60 Pages) TI2

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For n = 1.004 and T(°C) = 100°C, use Equation 5:

ERR

1.004

1.008

273.15

100 C

1.008

1.48 C

· u

(5)

If a discrete transistor is used as the remote temperature sensor, please select the transistor according to the

following criteria, which results in the best accuracy.

1. Base-emitter voltage > 0.25V at 6µA, at the highest sensed temperature.

2. Base-emitter voltage < 0.95V at 120µA, at the lowest sensed temperature.

3. Base resistance < 100Ω

4. Tight control of VBE characteristics is indicated by small variations in hFE (that is, 50 to 150).

Based on these criteria, use two small-signal transistors, such as the 2N3904 (NPN) or 2N3906 (PNP).

9.2.2 Detailed Design Procedure

The temperature measurement accuracy of the TMP411-Q1 and TMP411D-Q1 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 typically not a

concern.

The local temperature sensor inside the TMP411-Q1 and TMP411D-Q1 monitors the ambient air around the

device. The thermal time constant for the TMP411-Q1 and TMP411D-Q1 devices is approximately two seconds.

This constant implies that if the ambient air changes quickly by 100°C, the TMP411-Q1 and TMP411D-Q1 take

approximately 10 seconds (that is, five thermal time constants) to settle within 1°C of the final value. In most

applications, the TMP411-Q1 and TMP411D-Q1 package is in electrical (and thermal contact) with the printed

circuit board (PCB), and is 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-Q1 and TMP411D-Q1 can cause the

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

the remote temperature sensor is negligible because of the small currents used.

TMP411-Q1 (Legacy Chip): For a 5.5V supply and maximum conversion rate of eight conversions per second,

the TMP411-Q1 dissipates 2.2mW (PD IQ = 5.5V × 400µA). If the ALERT/ THERM2 and THERM pins are each

sinking 1mA, an additional power of 0.8mW is dissipated (PD OUT = 1mA × 0.4V + 1mA × 0.4V = 0.8mW).

Total power dissipation equals 3mW (PD IQ + PD OUT) and (with a θJA value of 150°C/W) causes the junction

temperature to rise approximately 0.45°C above the ambient.

TMP411-Q1 (New Chip): For a 5.5V supply and maximum conversion rate of eight conversions per second, the

TMP411-Q1 dissipates 0.248mW (PD IQ = 5.5V × 45µA). If the ALERT/ THERM2 and THERM pins are each

sinking 1mA, an additional power of 0.8mW is dissipated (PD OUT = 1mA × 0.4V + 1mA × 0.4V = 0.8mW). Total

power dissipation equals 1.048mW (PD IQ + PD OUT) and (with a θJA value of 162°C/W) causes the junction

temperature to rise approximately 0.170°C above the ambient.

TMP411D-Q1: For a 5.5V supply and maximum conversion rate of eight conversions per second, the TMP411D-

Q1 dissipates 0.248mW (PD IQ = 5.5V × 45µA). If the ALERT/ THERM2 and THERM pins are each sinking

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

power dissipation equals 1.048mW (PD IQ + PD OUT) and (with a θJA value of 182°C/W) causes the junction

temperature to rise approximately 0.191°C above the ambient.

TMP411-Q1, TMP411D-Q1

SBOS527G – DECEMBER 2010 – REVISED SEPTEMBER 2025

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