Datasheet > AVR401

AVR401

更新时间： 2024-11-22 06:38:47

品牌	Logo	应用领域
爱特美尔 - ATMEL		转换器
页数	文件大小	规格书
12页	120K
描述
8-bit Precision A/D Converter

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AVR401 数据手册

AVR401: 8-bit Precision A/D Converter

Features

8-bit

Microcontroller

• Very Low Cost

• High Precision

• Auto-calibration Eliminates Component Inaccuracy

• Measures Voltages for 0 to V_CC

• Maximum Conversion Time: 1.1 ms

Application

Note

Introduction

This application note describes how to perform a kind of dual slope A/D conversion

with an AVR microcontroller. The converter is very low cost, requiring only six discrete

components in addition to the AVR. Five of the controller pins are used (see Figure 1).

This example is based on the AT90S1200 device, but any AVR device with a compar-

ator can be used.

Figure 1. A/D Converter

V_CC

R_B

AT90S1200

PB7

(AIN0) PB0

(AIN1) PB1

PB2

R_{ref 1}

(V_ref)

V_in

R_in

R_{ref 2}

PB3

Theory of Operation

The capacitor is charged with a constant current supplied by the transistor. The

capacitor voltage will rise linearly. To discharge the capacitor, the AIN0-pin is set to

output with a “0” applied. A reference voltage at V_CC/2 is supplied by the resistor net-

work R_ref1and R_ref2. When the PB1 and PB2-pins are configured as inputs, the

reference is turned off, and the voltage level at the AIN1-pin will be the input voltage

V_in. By setting the pins as outputs and applying a “0” and a “1”, the level at the AIN1-

pin will be V_CC/2 (if the resistors are of equal size). The input resistor R_inhave to be at

least 100 times higher than the reference resistors R_ref1and R_ref2to avoid measure-

ment errors.

Rev. 0953C–AVR–02/03

12 3 4 5 6 7...12

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