Reverse Compatibility of the D

文章摘要：Abstract: Since many applications don't need the ±0.5°C accuracy of the DS1621 2-wire digital temperature sensor, the ±1.0°C accuracy DS1721 temperature sensor IC was created to provide a lower-cost alternative to the DS1621. In most respects, the DS1621 and DS1721 operate the same; however, the

Reverse Compatibility of the D,标签：计算机控制技术,工厂电气控制技术,http://www.88dzw.com
Abstract: Since many applications don't need the ±0.5°C accuracy of the DS1621 2-wire digital temperature sensor, the ±1.0°C accuracy DS1721 temperature sensor IC was created to provide a lower-cost alternative to the DS1621. In most respects, the DS1621 and DS1721 operate the same; however, there are a few differences between the devices that can result in software incompatibilities when transitioning from the DS1621 to the DS1721. This application note explains how the DS1721 differs from the DS1621, and how it will operate in circuits designed for the DS1621. It is aimed at users who are interested in transitioning from the DS1621 to the DS1721 and: a) want to find out if the DS1721 can be used as a drop-in replacement for the DS1621 in their design, or b) are at a point in their design cycle where it is still possible to make software modifications to accommodate the DS1721.

Overview

As Dallas Semiconductor continues to improve its line of thermal management products, a primary goal is to make these products more affordable. Since many applications do not need the ±0.5°C accuracy of the DS1621 2-Wire Digital Thermometer and Thermostat, the DS1721 was created to provide ±1.0°C accuracy at a lower cost than the DS1621. In most respects, the DS1621 and DS1721 operate the same; however, there are a few differences between the devices that can result in software incompatibilities when transitioning from the DS1621 to the DS1721.

This application note explains how the DS1721 differs from the DS1621, and how it will operate in circuits designed for the DS1621. It is aimed at users who are interested in transitioning from the DS1621 to the DS1721 and: a) want to find out if the DS1721 can be used as a drop-in replacement for the DS1621 in their design, or b) are at a point in their design cycle where it is still possible to make software modifications to accommodate the DS1721. Users who are starting a new design using the DS1721 should refer to the DS1721 datasheet for usage instructions, as information in this application note will not be pertinent. In addition, users that are transitioning from the DS1621 to the DS1721 will also need to refer to the DS1721 datasheet for device specifications and other information not covered in this application note.

Changes/cost reductions implemented in the design of the DS1721 are as follows:

1. The DS1721 uses a precision bandgap voltage reference and a ΣΔ A/D converter to provide temperature data in a digital format. The DS1621 achieves this function with a pair of oscillators, one with a positive temperature coefficient and the other with a zero temperature coefficient.
2. The DS1721 doesn't have EEPROM; the DS1621 does have EEPROM (i.e., non-volatile memory).
3. Because the DS1721 doesn't have EEPROM, it is calibrated via laser, a less expensive technique than the DS1621's bath calibration.

Dallas designed the DS1721 to be as compatible as possible with the DS1621, but items 1 and 2 above can create software discrepancies that may disallow the use of the DS1721 as a drop-in replacement for some DS1621 applications. Item 3 only relates to the lower accuracy of the DS1721 and does not affect software compatibility.

This application note addresses the following items that are of concern for DS1621/DS1721 compatibility:

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