T

=

ERR

h

1.008

-

1.008

(273.15+T( C))

°

´

TMP461

D+

D-

SCL

SDA

THERM

GND

V+

ALERT/THERM2

Processor or ASIC

SMBus

Controller

1

2

3

4

6

9

8

7

1.7 V to 3.6 V

1.7 V to 3.6 V

Built-In Thermal

Transistor, Diode

Overtemperature Shutdown

10

5

A1

A0

24

TMP461

SBOS722B – JUNE 2015 – REVISED AUGUST 2016

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Copyright © 2015–2016, Texas Instruments Incorporated

Typical Application (continued)

Figure 19. TMP461 Basic Connections Using a Processor Built-In Remote Transistor

9.2.1 Design Requirements

The TMP461 device is designed to be used with either discrete transistors or substrate transistors built into

processor chips and application-specific integrated circuits (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 18).

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

excitation used by the TMP461 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 TMP461 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 TMP461 allows for different η-factor values; see the η-Factor Correction Register section.

The ideality factor for the TMP461 device is trimmed to be 1.008. For transistors that have an ideality factor that

does not match the TMP461, Equation 4 can be used to calculate the temperature error.

NOTE

For Equation 4 to be used correctly, the actual temperature (°C) must be converted to

Kelvin (K).

where

•

TERR = error in the TMP461 device because η ≠ 1.008,

•

η = ideality factor of the remote temperature sensor,

•

T(°C) = actual temperature, and

(4)

In Equation 4, the degree of delta is the same for °C and K.