TMP411CD datasheet(42/61 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 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 indicated by small variations in hFE (that is, 50 to 150).

Based on these criteria, TI recommends using 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/TMP411D 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/TMP411D monitors the ambient air around the device. The

thermal time constant for the TMP411/TMP411D is approximately two seconds. This constant implies that if

the ambient air changes quickly by 100°C, the TMP411/TMP411D takes approximately 10 seconds (that is,

five thermal time constants) to settle within 1°C of the final value. In most applications, the TMP411/TMP411D

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/TMP411D 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 (Legacy Chip): For a 3.3V supply and maximum conversion rate of eight conversions per second,

the TMP411 dissipates 1.32mW (PD IQ = 3.3V × 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 2.12mW (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.

TMP411 (New Chip): For a 3.3V supply and maximum conversion rate of eight conversions per second, the

TMP411 dissipates 0.149mW (PD IQ = 3.3V × 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 0.949mW (PD IQ + PD OUT) and (with a θJA value of 162°C/W) causes the junction

temperature to rise approximately 0.154°C above the ambient.

TMP411D: For a 3.3V supply and maximum conversion rate of eight conversions per second, the TMP411D

dissipates 0.149mW (PD IQ = 3.3V × 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 0.949mW (PD IQ + PD OUT) and (with a θJA value of 182°C/W) causes the junction

temperature to rise approximately 0.173°C above the ambient.

TMP411, TMP411D

SBOS383E – DECEMBER 2006 – REVISED JULY 2025

www.ti.com

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