T

=

ERR

h

1.008

-

1.008

(273.15+T( C))

°

´

DXP

DXN

SCL

SDA

THERM

GND

V+

ALERT / THERM2

Processor or

ASIC

SMBus

Controller

1

2

3

4

5

8

7

6

TMP451

1.7V to 3.6V

1.7V to 3.6V

Built-in Thermal

Transistor/Diode

Overtemperature Shutdown

TMP451

SBOS686A – JUNE 2013 – REVISED DECEMBER 2014

www.ti.com

Typical Application (continued)

Figure 42. TMP451 Basic Connections Using a Processor Built-In Remote Transistor

8.2.1 Design Requirements

The TMP451 device is designed to be used with either discrete transistors or substrate transistors built into

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

used as the remote temperature sense. NPN transistors must be diode-connected. PNP transistors can either be

transistor- or diode-connected (see Figure 41).

Errors in remote temperature sensor readings are typically the consequence of the ideality factor and current

excitation used by the TMP451 device 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 TMP451 device uses 7.5

μA for ILOW and 120 μA for IHIGH.

The ideality factor (

η) is a measured characteristic of a remote temperature sensor diode as compared to an

ideal diode. The TMP451 allows for different

η-factor values; see the η-Factor Correction Register section.

The ideality factor for the TMP451 device is trimmed to be 1.008. For transistors that have an ideality factor that

does not match the TMP451, Equation 4 can be used to calculate the temperature error.

NOTE

For the equation to be used correctly, actual temperature (°C) must be converted to Kelvin

(K).

where

•

TERR = error in the TMP451 device because η ≠ 1.008

•

η = ideality factor of remote temperature sensor

•

T(°C) = actual temperature

•

Degree delta is the same for °C and K.

(4)

30

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