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TCN75A

2-Wire Serial Temperature Sensor

Microchip Technology 

TCN75A

5.0 FUNCTIONAL DESCRIPTION

The TCN75A temperature sensor consists of a band-

gap type temperature sensor, a ΣΔ Analog-to-Digital

Converter (ADC), user-programmable registers and a

2-wire I2C protocol-compatible serial interface.

Resolution

One-Shot

Shutdown

Fault Queue

Alert Polarity

Alert Comp/Int

Configuration

Register

Temperature

Register

THYST

Register

TSET

Register

0.5°C

0.25°C

0.125°C

0.0625°C

ΣΔ ADC

Band-Gap

Temperature

Sensor

Register

Pointer

I2C™

Interface

FIGURE 5-1:

Functional Block Diagram.

5.1 Temperature Sensor

The TCN75A uses the difference in the base-emitter

voltage of a transistor while its collector current is

changed from IC1 to IC2. With this method, the ΔVBE

depends only on the ratio of the two currents and the

ambient temperature, as shown in Equation 5-1.

EQUATION 5-1:

ΔVBE

=

⎛

⎝

k--q--T-⎠⎞

× ln(IC1 ⁄ IC2)

Where:

T = temperature in kelvin

ΔVBE = change in diode base-emitter

voltage

k = Boltzmann's constant

q = electron charge

IC1 and IC2 = currents with n:1 ratio

5.2 ΣΔ Analog-to-Digital Converter

A Sigma-Delta ADC is used to convert ΔVBE to a digital

word that corresponds to the transistor temperature.

The converter has an adjustable resolution from 0.5°C

(at 30 ms conversion time) to 0.0625°C (at 240 ms

conversion time). Thus, it allows the user to make trade-

offs between resolution and conversion time. Refer to

Section 5.3.2 “Sensor Configuration Register

(CONFIG)” and Section 5.3.4.7 “ΣΔ ADC Resolution”

for details.

DS21935C-page 10

© 2006 Microchip Technology Inc.

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