TCN75AVUA datasheet(13/40 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

DS21935D-page 13

TCN75A

5.0

FUNCTIONAL DESCRIPTION

The TCN75A temperature sensor consists of a band-

gap type temperature sensor, a

 Analog-to-Digital

Converter (ADC), user-programmable registers and a

2-wire I2C protocol-compatible serial 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 VBE

depends only on the ratio of the two currents and the

ambient temperature, as shown in Equation 5-1.

EQUATION 5-1:

5.2

 Analog-to-Digital Converter

A Sigma-Delta ADC is used to convert

VBE 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

and Section 5.3.4.7 “

 ADC

Resolution”

for details.

Resolution

0.5°C

0.25°C

0.125°C

0.0625°C

Temperature

THYST

TSET

Pointer

I2C™

Interface

Configuration

 ADC

Band-Gap

Temperature

Sensor

One-Shot

Shutdown

Fault Queue

Alert Polarity

Alert Comp/Int

V

------





ln IC

1 IC2







Where:

T = temperature in kelvin

VBE = change in diode base-emitter

voltage

k = Boltzmann’s constant

q = electron charge

IC1 and IC2 = currents with n:1 ratio

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