MCP9801 datasheet(8/30 Pages) MICROCHIP

8 / 30 page

MCP9800/1/2/3

DS21909B-page 8

 2004 Microchip Technology Inc.

4.0

FUNCTIONAL DESCRIPTION

The MCP9800/1/2/3 family of temperature sensors

consists of a band-gap type temperature sensor, a

Σ∆

Analog-to-Digital Converter (ADC), user-programmable

registers and a 2-wire I2C/SMBus protocol compatible

serial interface.

FIGURE 4-1:

Functional Block Diagram.

4.1

Temperature Sensor

The MCP9800/1/2/3 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 4-1.

EQUATION 4-1:

4.2

Σ∆ Analog-to-Digital Converter

A sigma-delta analog-to-digital converter is used to

convert

∆V

BE to a digital word that corresponds to the

transistor

temperature.

The

converter

has

adjustable resolution from 9-bits (at 30 ms conversion

time) to 12-bits (at 240 ms conversion time). Thus, it

allows the user to make trade-offs between resolution

and conversion time. Refer to Section 4.3.4 “Sensor

Configuration

(CONFIG)”

and

Section 4.3.4.7 “

Σ∆ ADC Resolution” for details.

Resolution

9-Bit

10-Bit

11-Bit

12-Bit

Temperature

THYST

TSET

Pointer

I2C™/SMBus

Interface

Configuration

Σ∆ 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

∆V

BE = 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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