TMP411CD datasheet(41/61 Pages) TI2

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9.2 Typical Application

9.2.1 Design Requirements

The TMP411/TMP411D is designed to be used with discrete transistors or substrate transistors built into

processor chips and ASICs. NPN or PNP transistors can be used, as long as the base-emitter junction is

the remote temperature sensor. A transistor or diode connection can be used, as shown in Figure 7-1. The D+

pin waveform is shown in Figure 9-3 while a transistor is connected between the D+ and D– pins. Due to 3

different source currents shown in Functional Block Diagram, the D+ waveform has 3 levels of voltages during

temperature conversion.

Time (s)

0.01

0.02

0.03

0.04

0.05

-0.2

0.2

0.4

0.6

0.8

Time (s)

0.02

0.0208

0.0216

0.0224

0.0232

0.024

0.5

0.55

0.6

0.65

0.7

Temperature

Conversion

Figure 9-3. D+ Waveform

Errors in remote temperature sensor readings are the result of the ideality factor and current excitation

from the TMP411/TMP411D versus the manufacturer-specified operating current for a given transistor. Some

manufacturers specify a high-level and low-level current for the temperature-sensing substrate transistors. The

TMP411/TMP411D has an ILOW value of 6μA, and an IHIGH value of 120μA. The TMP411/TMP411D allows for

different n-factor values, as shown in Table 8-6.

The ideality factor (n) is a measured characteristic of a remote temperature sensor diode compared to an ideal

diode. The ideality factor reduces to a value of 1.008. For transistors with an ideality factor that does not match

the TMP411/TMP411D, Equation 4 calculates the temperature error. Note that the actual temperature (°C) must

be converted to Kelvin (°K) for the equation to yield the correct results.

ERR

n 1.008

273.15

T( C)

1.008

· u

TERR= nactual − nexpected

nexpected × 273.15+Tactual

(4)

where:

• n or nactual = the ideality factor of the remote temperature sensor

• T(°C) or Tactual(°C) = actual temperature

• TERR = Treported - Tactual= device reading error due to n or nactual ≠ 1.008

• Degree delta is the same for °C and °K

• nexpected = 1.008

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TMP411, TMP411D

SBOS383E – DECEMBER 2006 – REVISED JULY 2025

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