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<p><span>作者：Richard Anslow</span></p>

<p><span>简介</span></p>

<p><span>ADI公司的</span><span>i</span><span>Coupler</span><span>®</span><span>数字隔离器和RS-485收发器产品系列解决了工业应用中的两大需求：更高的数据速率和更低功耗的工作模式。</span></p>

<p><span>对于高性能电机控制编码器应用而言，通常需要更高的数据速率、更小的RS-485收发器封装和IEC 61000-4-2 ESD保护。</span><span>ADM3065E</span><span>/</span><span>ADM3066E</span><span><span>&nbsp;<span>&nbsp;</span></span></span><span>50 Mbps收发器采用节省空间的10引脚</span><span><span>&nbsp;</span></span><span>LFCSP封装，可提供±12 kV（接触）和±12 kV（空气）的IEC</span><span><span>&nbsp;</span></span><span>61000-4-2 ESD保护功能，为</span><span><span>&nbsp;</span></span><span>EnDat编码器提供了一套可靠的解决方案（请参考</span><span>AN-1397应用笔记</span><span>了解更多</span><span><span>&nbsp;</span></span><span>信息）。此</span><span>外，</span><span>在</span><span>ADM3065E</span><span>/</span><span>ADM3066E<span>&nbsp;</span></span><span>中添加高速稳定的信号和功率隔离可以通过</span><span><span>&nbsp;</span></span><span>iso</span><span>Power</span><span>®</span><span><span>&nbsp;</span></span><span>ADuM6401</span><span>或<span>&nbsp;</span></span><span>iso</span><span>Power<span>&nbsp;</span></span><span>ADuM6000<span>&nbsp;</span></span><span>及</span><span><span>&nbsp;</span></span><span>i</span><span>Coupler<span>&nbsp;</span></span><span>ADuM241D</span><span>来实现，如本应用笔记中所述。</span></p>

<p><span>在电池供电系统、井下应用（例如，采矿）以及在4 mA至20 mA环路中工作的过程控制系统中，往往对低功耗工作模式具有较高需求。ADI公司生产的微功耗数字隔离器</span><span>ADuM1441</span><span>在关断模式下的静态功耗低于23 μA。</span><span>ADM3483</span><span><span>&nbsp;</span></span><span>3.3 V、250 kbps RS-485收发器的静态功耗极低，关断模式下通常仅2 nA。</span></p>

<p><span>图1所示为适合井下应用稳定可靠的低功耗隔离式RS-485解决方案。</span><span>ADM3483</span><span>和</span><span>ADuM1441</span><span>共用可提供一条通往远程地下测量节点的可靠低功耗链路。系统接口卡包括ARM</span><span>®</span><span><span>&nbsp;</span>Cortex</span><span>®</span><span><span>&nbsp;</span>微控制器单元(MCU)、</span><span>ADuCM3027</span><span>和集成模拟前端(AFE)</span><span>AD7124-4</span><span>，用于远程温度和压力测量。系统接口卡的固件更新通过远距离RS-485电缆提供，更新后能够在最长1 km的远距离内实现低数据速率传输（例如，9.6 kbps）。</span></p>

<p><img alt="图1.适合井下应用稳定可靠的低功耗隔离式RS-485解决方案" data-entity-type="file" data-entity-uuid="183df3a5-f2ba-488c-866f-85235fa198c8" src="http://new.eetrend.com/files/2021-01/wen_zhang_/100060940-119209-1.jpg&…; /></p>

<p><em><span>图1.适合井下应用稳定可靠的低功耗隔离式RS-485解决方案</span></em></p>

<p><span>隔离式高速RS-485</span></p>

<p><span>利用</span><span>i</span><span>Coupler</span><span>和</span><span>iso</span><span>Power</span><span>技术</span><span>，</span><span>可以向</span><span>ADM3065E</span><span>中增添兼具加强绝缘和</span><span>5 kV rms</span><span>瞬态耐受电压的电流隔离。</span><span>ADuM6401</span><span>提供了所需的四通道5 kV rms信号隔离、最高25 Mbps的工作速率以及集成式DC/DC转换器。</span><span>ADuM6401</span><span>配合</span><span>ADM3065E</span><span>（如图2所示）需将</span><span>V</span><span>ISO</span><span>引脚配置为3.3 V，具体方法是将</span><span>V</span><span>SEL</span><span>引脚连接到</span><span>GND</span><span>ISO</span><span>引脚，并将5V电源连接到</span><span>V</span><span>DD1</span><span>引脚。</span><span>在3.3V电压下工作，即使数据速率达25 Mbps，也可以确保</span><span>ADM3065E</span><span>仍保持在</span><span>ADuM6401</span><span>的负载能力范围内。</span></p>

<p><span>利用</span><span>ADuM241D</span><span>四通道数字隔离器和</span><span>ADuM6000</span><span>隔离式DC/DC转换器，可以实现50 Mbps数据速率以及</span><span>ADM3065E</span><span>隔离，如图3所示。</span><span>ADuM241D</span><span>的数据速率最高可达150 Mbps，能够提供完全支持</span><span>ADM3065E</span><span>以50 Mbps数据速率工作所需的精确时序。</span></p>

<p><span>不过，以50 Mbps数据速率工作的前提是使</span><span>ADM3065E</span><span>工作在3.3 V电压下。</span></p>

<p><span>如果需要在5V电压下工作，可以将</span><span>ADuM6000</span><span>上的</span><span>V</span><span>SEL</span><span>引脚连接到</span><span>V</span><span>ISO</span><span>，但支持的最大数据速率会降低（例如，&lt;10 Mbps）。更多信息，请参考</span><span>ADuM241D</span><span>和</span><span>ADuM6000</span><span>数据手册。</span></p>

<p><span>ADuM6401</span><span>和</span><span>ADuM6000<span>&nbsp;</span></span><span>iso</span><span>Power</span><span>器件中的</span><span>DC/DC</span><span>转换器可为</span><span>ADM3065E</span><span>（</span><span>和</span><span>ADuM241D</span><span>）</span><span>提供稳压隔离电源。</span><span>这两款</span><span>iso</span><span>Power器件</span><span>利用高频开关元件，通过变压器传输功率。</span><span>用户必须遵循辐射标准进行印刷电路板(PCB)布局。</span><span>如需PCB布局建议，请参考</span><span>AN-0971应用笔记</span><span>。</span></p>

<p><img alt="图2.信号和电源隔离的25 Mbps RS-485解决方案（简化图，未显示全部连接）" data-entity-type="file" data-entity-uuid="fb9f8cfd-a842-4702-be55-b44d131b24ad" src="http://new.eetrend.com/files/2021-01/wen_zhang_/100060940-119210-2.jpg&…; /></p>

<p><em><span>图2.信号和电源隔离的25 Mbps RS-485解决方案（简化图，未显示全部连接）</span></em></p>

<p><img alt="图3.信号和电源隔离的50 Mbps RS-485解决方案（简化图，未显示全部连接）" data-entity-type="file" data-entity-uuid="6c93d30b-416b-45d7-bf3b-dd03d78332c9" src="http://new.eetrend.com/files/2021-01/wen_zhang_/100060940-119211-3.jpg&…; /></p>

<p><em><span>图3.信号和电源隔离的50 Mbps RS-485解决方案（简化图，未显示全部连接）</span></em></p>

<p><span>隔离式低功耗</span><span>RS-485</span></p>

<p><span>图4显示了</span><span>ADuM1441</span><span>微功耗、四通道、数字隔离器和</span><span>ADM3483</span><span>低功耗、半双工RS-485收发器的组合。</span></p>

<p><span>当</span><span>ADM3483</span><span>处于关断模式（驱动器使能DE引脚为低电平且接收器使能</span><span><span>RE)</span></span><span>引脚为高电平）时，静态电源电流通常仅为2 nA（最大规范值为1 μA）。如图</span><span>4所示，</span><span>ADuM1441</span><span>的引脚7和引脚10分别连接至GND</span><span>1</span><span>和GND</span><span>2</span><span>。</span><span>这意味着当</span><span>ADuM1441</span><span>隔离器处于无总线通信活动的关断模式时，其静态电流低于23 µA。</span><span>总体来说，该解决方案的静态功耗低至24 µA以下。</span></p>

<p><span>如果</span><span>ADuM1441</span><span>的引脚7和引脚10分别直接连接到V</span><span>DD1</span><span>和V</span><span>DD2</span><span>，</span><span>则</span><span>ADuM1441</span><span>的静态功耗仅1.2 µA。</span><span>这可以通过</span><span>PCB上的跳线连接来实现，用户可以选择将引脚7连接到V</span><span>DD1</span><span>或GND</span><span>1</span><span>，还可以选择将引脚10连接到V</span><span>DD2</span><span>或GND</span><span>2</span><span>。</span><span>将</span><span>ADuM1441</span><span>中的1.2 μA静态功耗特性添加到</span><span>ADM3483</span><span>静态电源中，可实现一个在关断或待机模式下仅消耗2 μA电流的完全隔离式RS-485节点。为了确保隔离器正常工作，</span><span>ADuM1441</span><span>的引脚7和引脚10必须分别连接到GND</span><span>1</span><span>和GND</span><span>2</span><span>。</span></p>

<p><img alt="图4.低功耗、隔离式RS-485节点" data-entity-type="file" data-entity-uuid="a9b5d4ad-cbcc-47e9-b026-c263023d17f2" src="http://new.eetrend.com/files/2021-01/wen_zhang_/100060940-119212-4.jpg&…; /></p>

<p><em><span>图4.低功耗、隔离式RS-485节点</span></em></p>