8 Detailed Description

8.1 Overview

The TMP64 silicon linear thermistor has a linear positive temperature coefficient (PTC) that results in a uniform

and consistent temperature coefficient resistance (TCR) across a wide operating temperature range. TI uses a

special silicon process where the the doping level and active region areas devices control the key characteristics

(the temperature coefficient resistance (TCR) and nominal resistance (R25)) . The device has an active area and

a substrate due to the polarized terminals. Connect the positive terminal to the highest voltage potential.

Connect the negative terminal to the lowest voltage potential.

Unlike an NTC, which is a purely resistive device, the TMP64 resistance is affected by the current across the

device and the resistance changes when the temperature changes. In a voltage divider circuit, it is

recommended to maintain the top resistor value at 47 kΩ. Changing the top resistor value or the VBIAS value

changes the resistance vs temperature table (R-T table) of the TMP64, and subsequently the polynomials as

described in Section 9.2.1.1. Consult Section 8.3.1 for more information.

TCR (ppm/°C) = (RT2 – RT1) / ((T2 – T1) × R(T2+T1)/2)

(1)

Below are the definitions of the key terms used throughout this document:

• ISNS: Current flowing through the TMP64.

• VSNS: Voltage across the two TMP64 terminals.

• IBias: Current supplied by the biasing circuit.

• VBias: Voltage supplied by the biasing circuit.

• VTemp: Output voltage that corresponds to the measured temperature. Note that this is different from VSns. In

the use case of a voltage divider circuit with the TMP64 in the high side, VTemp is taken across RBias.

8.2 Functional Block Diagram

RBias

VBias

VTemp

RTMP64

VTemp

RTMP64

IBias

Figure 8-1. Typical Implementation Circuits

TMP64

SNIS212C – DECEMBER 2019 – REVISED SEPTEMBER 2020

www.ti.com

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