单片机VDD波形上传递的“密码”
本帖最后由 onemoren 于 2022-5-10 20:26 编辑大家单片机玩得很溜了，平时也很少去关注VDD波形，整机测试无异常就完事了。也确实，芯片技术发展多年，芯片厂家对芯片可靠性也做足了功夫，VDD上的波动一般不影响单片机工作。但是，作为一个细心、负责的电子工程师，日常开发工作中，还是应该多了解一下自己设计的单片机系统，其VDD波形究竟如何。如果有异常的波动，应该找出原因并评估风险，有些比较严重的掉电或波动，应该通过改进电路来保证整机可靠性。
下面举三个VDD波动的例子。如下三图所示（图2、图3中的下凹为us级）大家可以试试判断VDD上发生了什么事情，VDD波形传递了什么“密码”。
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***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
图1中，VDD电平被拉低，通常是VDD供电域中，某个（或某些）模块或电路开启运行且功耗很大，即整个VDD域的整体需求电流增加，而VDD前端的LDO或电源输出能力有限（内阻较大），最终看到VDD电平下降（大家可用电阻分压模型来理解下）。
图2中，VDD电平被拉低几十~几百us然后恢复原电平值。通常是VDD供电域中，某个（或某些）模块或电路接入或开启，而这个模块或电路上有大电容，在接入或开启的瞬间，大电容相当于短路到地，电流很大，VDD电平被拉下；但这个模块或电路工作时的功耗并不高，VDD前端的LDO或电源输出能够应付，所以VDD电平随后恢复到原值。
图3中，VDD电平被拉低几十~几百us然后恢复不到原电平值。通常是VDD供电域中，某个（或某些）模块或电路接入或开启，而这个模块或电路上有大电容，在接入或开启的瞬间，大电容相当于短路到地，电流很大，VDD电平被拉下；某个（或某些）模块或电路工作时的功耗很高，即整个VDD域的整体需求电流增加，而VDD前端的LDO或电源输出能力有限（内阻较大），最终看到VDD电平比之前有所下降。
以上只是举例说明VDD波形上的变化其实提供了很多关键信息，这些信息可让大家更了解自己的电路，指导我们如何改进电路，如何提高可靠性。
下次大家抓取到VDD上的波形，不妨多分析多思考VDD的“密码”。
图片是忘了放进去吗 补充图片再学习一下 因为MCU的供电范围很宽，平时确实很少考虑到。 我晕，还以为是啥。 mark一下~留作参考~
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