【经验】使用肖特基二极管设计输入保护电路，防止ADC击穿现象

时间： 2021-03-05 来源：世强

技术问答

某客户设计一款电子秤项目，采用3PEAK 3PA9280作为输入采样ADC，单电源供电，在应用中放大器采用±15 V供电，而ADC输入为0至5V。高压电轨用于接受±10 V输入，同时给ADC前端信号调理/驱动级供电。放大器驱动电源电压偶尔会出现不稳定情况，因超过最大额定值而损坏ADC，本文主要帮助客户介绍一种输入保护电路。

客户设计的典型ADC采集电路如下：ADC为3PEAK 3PA9280。

客户在实际测试时经常会出现ADC击穿现象，检测之后发现是因为放大器电源轨±15V，输入波动较大，ADC设计输入为0-5V，解决此问题最常见的就是使用一颗肖特基二极管，将放大器输入钳位在ADC的输入范围之内。如下所示：

在此情况中，之所以选择肖特基二极管，是因为其具有低正向导通压降，可在ADC内的内部保护二极管之前开启。如果内部二极管部分开启，肖特基二极管后的串联电阻也有助于将电流限制在ADC内。对于额外保护，如果基准电压源没有/几乎没有灌电流能力，则可在基准节点上采用齐纳二极管或箝位电路，以保证基准电压不被过度拉高。在图2中，为5V基准电压源使用了5.6V齐纳二极管。

如上文所述，保护ADC输入可以设计钳位二极管的方案。但根据应用要求，可采用不同的单独或组合方法，以相应的性能取舍提供所需的保护水平。

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