Buck电路输入电容放置有讲究-MPS文档
本帖最后由 qwqwqw2088 于 2024-11-1 10:42 编辑<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-top: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><a href="https://bbs.eeworld.com.cn/thread-1297985-1-1.html" target="_blank"><u>Buck电路输入电容放置有讲究-MPS文档</u></a></p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-top: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Buck电源芯片在layout过程中，输入电容应当如何放置以及放置不好对芯片工作有何影响？来谈一谈Buck电路输入电容位置放置的问题。<br />
众所周知，Buck变换器在使用过程中，欲使输入端以最小的纹波代价，快速提供Buck变换器每个开关周期所需要的能量，输入端的MLCC是必不可少的；</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/51e47f510f3a2b0f1835532c329c59015bed6f48" href="https://forum.monolithicpower.cn/uploads/default/original/2X/5/51e47f510f3a2b0f1835532c329c59015bed6f48.jpeg" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<em>图1：Buck变换器开关周期图</em>
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<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">那么在实际layout的过程中，输入端的MLCC摆放到底有什么讲究呢？<br />
带着这个疑问，我们查阅MPS的大电流Buck变换器 MP87XXX的 Layout Guidelines一探究竟：</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
<p><strong>MP87XXX PCB Layout Guidelines：</strong><br />
<strong>1. Place the MLCC input capacitors as close to VIN and PGND as possible.</strong><br />
输入MLCC尽可能的靠近芯片VIN和PGND pin脚放置；</p>
<p><strong>2. Place as many VIN and PGND vias underneath the package as possible. Place these vias between the VIN or PGND long pads.</strong><br />
在芯片下方尽可能的多放置Vin和PGND的通孔，且通孔需要放置在芯片的VIN或者PGND的pad上；</p>
<p><strong>3. Place a VIN copper plane mid-layer 2 to form the PCB stack (positive/negative/positive) to reduce parasitic impedance from the MLCC input capacitor to the MP87000.</strong><br />
在PCB的L2层铺VIN的铜皮网络，使得Top层，L1层和L2层形成正/负/正的堆叠 结构，其目的是减小输入MLCC到MP87000的寄生阻抗。</p>
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<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Layout guidelines提到的这3点，究竟是从什么方面去考量的呢？下面我们对其进行逐条分析：</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><strong>1. Place the MLCC input capacitors as close to VIN and PGND as possible.</strong><br />
输入MLCC尽可能的靠近芯片VIN和PGND pin脚放置；</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/cebd54af5010700a669b64f9bf444a0df55d332b" href="https://forum.monolithicpower.cn/uploads/default/original/2X/c/cebd54af5010700a669b64f9bf444a0df55d332b.jpeg" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<em>图2：顶视图和底视图</em>
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<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">我们简化输入MLCC到芯片VIN和PGND pin脚的Layout模型如下：</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/59acaf6af5165dd54cf6d804ca2ed54ccdcd3f41" href="https://forum.monolithicpower.cn/uploads/default/original/2X/5/59acaf6af5165dd54cf6d804ca2ed54ccdcd3f41.png" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<em>图3：简化后的芯片Layout模型图</em>
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<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">其中Ctop为top面的输入MLCC，Cbottom为Bottom面的输入MLCC，L1和L2分别为Top面输入MLCC到芯片VIN和PGND的寄生电感，L3和L4分别为Bottom面输入MLCC的VIN和PGND过孔的寄生电感，通过简化模型可以看出，输入MLCC靠近芯片VIN和PGND pin脚放置可以减小寄生电感L1和L2；</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><strong>2. Place as many VIN and PGND vias underneath the package as possible. Place these vias between the VIN or PGND long pads.</strong></p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">在芯片下方尽可能的多放置VIN和PGND的通孔，且通孔需要放置在芯片的VIN或者PGND的Pad上；</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/31f3c89f4098f7be87566f987be2851d8131ad17" href="https://forum.monolithicpower.cn/uploads/default/original/2X/3/31f3c89f4098f7be87566f987be2851d8131ad17.png" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<em>图4：MLCC到芯片VIN和PGND Pin脚的寄生电感</em>
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<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">对于Top面的MLCC来说，打VIN和PGND的通孔，除了连接内层VIN和PGND的铜皮以外，本质上是增加了VIN和PGND的电流路径，除了增加通流能力以外，还会使得不同层间的寄生电感并联，达到减小输入MLCC到芯片VIN和PGND寄生电感的目的。</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">对于Bottom面的MLCC来说，多打VIN和PGND的通孔，除了使得Bottom面的MLCC有更好的滤波效果以外，同时也会使得通孔间的等效电感并联，达到减小寄生电感L3和L4的目的。</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><strong>3. Place a VIN copper plane mid-layer 2 to form the PCB stack (positive/negative/positive) to reduce parasitic impedance from the MLCC input capacitor to the MP87000.</strong><br />
在PCB的L2层铺VIN的铜皮网络，使得Top层，L1层和L2层形成正/负/正的堆叠结构，其目的是减小输入MLCC到MP87XXX 的寄生阻抗；<br />
MP87000 has not been released on MPS website yet. This part number is also mentioned in the video at 0:00:53.</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/85e1bc698cb6094710598545fbe926594fe5ef10" href="https://forum.monolithicpower.cn/uploads/default/original/2X/8/85e1bc698cb6094710598545fbe926594fe5ef10.png" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<em>图5：Top层、L1层和L2层形成正/负/正的堆叠结构</em>
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<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">我们都知道PCB的层与层之间相当于一个寄生电容，那么当在TOP层，L1和L2层铺成正/负/正的网络时，由于通孔的存在，相当于在芯片的VIN和PGND之间增加了很多寄生电容，等效增大了输入MLCC的容值。</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">另外增加VIN或者PGND层数，本身就会减小输入MLCC到芯片间的寄生电感，第二条有提到，就不 再赘述；</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">综上所述，对于Buck变换器来说，输入MLCC的放置，一定要朝着减小输入MLCC到芯片VIN和PGND pin脚寄生电感的方向去优化。</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">在Buck变换器下管电压应力测试中，当我们使用最小环测试芯片的SW 和PGND pin时仍然会看到如下类似波形，开关节点SW的上升沿和下降沿会产生很大的震荡，上升沿震荡的峰值远超过VIN电源电压，下降沿甚至会震荡到负值，过大的正压和负压都会造成下MOS管的损坏。</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">下面我们分别研究一下上升沿和下降沿尖峰产生原因。首先看一下上升沿尖峰产生的原因：</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/06e5c62dea52b8a9e01781150e92d6245577e853" href="https://forum.monolithicpower.cn/uploads/default/original/2X/0/06e5c62dea52b8a9e01781150e92d6245577e853.png" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<em>图6：上升沿和下降沿尖峰</em>
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<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">如下为Buck变换器等效模型：</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<em>图7：Buck变换器等效模型</em>
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</blockquote>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">其中Cin为输入MLCC且包含寄生ESL和ESR；L1和L4分别为输入MLCC到芯片VIN和PGND的寄生电感；L2与L3为Buck芯片内部上下管MOS的等效寄生和引线电感，对于集成MOS的Buck变换器来说，L2和L3由芯片工艺和内部走线决定；L5和C3分别为Buck变换器的输出电感和输出电容；本文对Cin电容的ESL,ESR和L2,L3不做过多分析，重点讨论L1和L4的大小对Buck变换器上下管电压应力的影响。</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"> </p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-top: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">下面我们通过仿真波形来辅助分析SW上升沿震荡产生的原因：</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
<p> </p>
<div style="vertical-align: middle;">
<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/bcaf5af32c3d0f80a78af5bda4ceeedbf4fdfce6" href="https://forum.monolithicpower.cn/uploads/default/original/2X/b/bcaf5af32c3d0f80a78af5bda4ceeedbf4fdfce6.jpeg" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
<div style="transition:opacity 0.2s; bottom: 0px; display: flex; opacity: 0; align-items: center;"> </div>
</div>
<br />
<em>图8：仿真波形图</em>
<p> </p>
</blockquote>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
<p>截取SW电压和下管体二极管iD2的波形，我们将波形分为Ⅲ部分：<br />
Ⅰ：t0-t1时刻，Q1和Q2都关断，此时电感L5的电流由二极管D2续流，可以看到SW有-0.7V左右的二极管压降；</p>
<div style="text-align: center;"></div>
<br />
<em>图9：t0-t1时刻</em>
<p> </p>
<p>Ⅱ：t1-t2时刻，t1时刻，Q1开通，此时二极管D2会承受来自Vin的反压，导致二极管电流迅速减小，由于二极管本身存在反向恢复，所以会看到二极管电流会变负；在这个过程中，D2,L3支路的电流减小，因此会在电感L3上面感生出上正下负的电压，这就是t1-t2时刻，SW第一段阶跃的原因；此时二极管D2仍在导通，C2还未进行充电；</p>
<div style="text-align: center;"></div>
<br />
<em>图10：t1-t2时刻</em>
<p> </p>
<p>Ⅲ：t2时刻之后，iD2的电流因为反向恢复变为负值，此刻进入第三阶段，谐振阶段；<br />
谐振阶段又可分为对C2充电和对C2放电二个阶段，仿真波形中增加电感L1和L3的电流iL1和iL3。<br />
通过仿真波形可以看到：</p>
<div style="vertical-align: middle;">
<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/3b345dc44b1264dd1a008f5a8c99ef3c64c1a78d" href="https://forum.monolithicpower.cn/uploads/default/original/2X/3/3b345dc44b1264dd1a008f5a8c99ef3c64c1a78d.png" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
</div>
<br />
<em>图11：谐振阶段波形图</em>
<p> </p>
</blockquote>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">t2-t3时刻，电感电流iL1同时对C2和L5充电，此时SW点电压慢慢爬升，由于SW点电压小于Vin电压，iL1电流不断增大，因为负载电流恒定，因此电感L3电流不断增大，直到SW电压等于Vin电压时，电感L1电流达到最大，C2继续被充电，SW电压高于Vin，之后电感L1电流开始减小，iL3也开始减小，直到为0，此时C2停止充电，SW电压到达最高点，且iL1等于负载电流；</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
<p> </p>
<div style="text-align: center;"></div>
<br />
<em>图12：t2-t3时刻</em>
<p> </p>
</blockquote>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">了解SW上升沿尖峰产生的原因之后，我们看一下L1和L4的大小对SW上升沿尖峰有什么影响呢？</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">由于这两个寄生的电感的大小在实际的PCB中很难去精准量化，所以我们通过仿真的方式进行验证。仿真参数如下，通过选取4组不同的L1和L4的电感值，读取max(Vsw)值，结果如下：</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
<p> </p>
<div style="vertical-align: middle;">
<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/ae5d515bcbfc24ad3793524460e52e43efc687be" href="https://forum.monolithicpower.cn/uploads/default/original/2X/a/ae5d515bcbfc24ad3793524460e52e43efc687be.png" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
<div style="transition:opacity 0.2s; bottom: 0px; display: flex; opacity: 0; align-items: center;"> </div>
</div>
<br />
<em>图14：仿真结果图</em>
<p> </p>
</blockquote>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">通过仿真可以看到，L1与L4任何一个电感的感量大小都对下管SW上升沿尖峰的Max值都有影响，且L1与L4的感值越大，下管的SW的正向尖峰越大；<br />
仿真参数如下：Vin=12V,Vo=0.8V,Io=40A,Fs=500K; L2=L3=500pH;C1=C2=5nF;Cin=40u,忽略寄生ESR,ESL;</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">下面我们介绍一下SW下降沿负尖峰产生的原因和影响因素。同样结合SW电压，iL1和iL3的电流仿真波形，可以看到：</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
<p> </p>
<div style="vertical-align: middle;">
<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/cd555dde14c1974fb130c845c9517fcd0e824ae3" href="https://forum.monolithicpower.cn/uploads/default/original/2X/c/cd555dde14c1974fb130c845c9517fcd0e824ae3.png" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
<div style="transition:opacity 0.2s; bottom: 0px; display: flex; opacity: 0; align-items: center;"> </div>
</div>
<br />
<em>图15：SW电压，iL1和iL3的电流仿真波形图</em>
<p> </p>
</blockquote>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">t0时刻，Q1关断时，Q2未开通时，输出电感L5电流可以近似认为不变，此时有两条电流支路为电感L5提供能量，分别为：</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><strong>Loop1：L1-C1-L5-C3-L4-Cin-L1</strong><br />
<strong>Loop2：C2-L3-L5-C3-C2</strong></p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">其中Loop1的电流在减小，Loop2的电流在增加；对于电感L3来说，电感电流突然增加，就会感生出下正上负的电压，因此在SW的下降沿会看到负压；</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
<p> </p>
<div style="text-align: center;"></div>
<br />
<em>图16：t0时刻电流流向图</em>
<p> </p>
</blockquote>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">通过仿真，L3分别选择不同的感值，仿真结果如下：</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
<p> </p>
<div style="vertical-align: middle;">
<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/b06160d46b88777077d5bb3717c9343f54944752" href="https://forum.monolithicpower.cn/uploads/default/original/2X/b/b06160d46b88777077d5bb3717c9343f54944752.png" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
<div style="transition:opacity 0.2s; bottom: 0px; display: flex; opacity: 0; align-items: center;"> </div>
</div>
<br />
<em>图17：L3分别选择不同的感值仿真结果图</em>
<p> </p>
</blockquote>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">通过仿真结果可知负压的大小跟寄生电感L3相关，且感值越大，负压越负。</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">同样我们用最小环测试Buck电路上管电压应力时，也会经常看到在上管关断时，VIN-SW出现很大的电压尖峰，这个尖峰过大，同样会损坏上管。下面我们看一下这个震荡尖峰产生的原因；</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
<p> </p>
<div style="vertical-align: middle;">
<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/92b74268c48deb48677d9dcd0b373a75b605a23b" href="https://forum.monolithicpower.cn/uploads/default/original/2X/9/92b74268c48deb48677d9dcd0b373a75b605a23b.jpeg" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
<div style="transition:opacity 0.2s; bottom: 0px; display: flex; opacity: 0; align-items: center;"> </div>
</div>
<br />
<em>图18： VIN-SW电压尖峰</em>
<p> </p>
</blockquote>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">结合VIN-SW电压和电感L1和L3的电流iL1和iL3的仿真波形，根据iL1的过0点，把整个过程可以分为Ⅱ个段：</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Ⅰ(t0-t1)：t0时刻，Q1关断，电感L1上的能量经过L1-C1-L5-C3-L4-Cin-L1对C1进行充电。 iL1电流不断减小，在iL1电流过0时，C1停止充电，此VIN-SW电压到达最高点，此时进入阶段Ⅱ；</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Ⅱ(t1-t2)：t1时刻，当iL1过0时，由于C1电压大于Vin，因此C1经过C1-L1-Cin-L4-Q2-L3-C1进行放电，直到iL1电流为0，C1停止放电，VIN-SW电压下降到最低点，然后重复Ⅰ和Ⅱ这两个过程，由于线路寄生电阻的存在，最终VIN-SW电压稳定在VIN；</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">在整个过程中电感L5上的能量经过L5-C3-Q2 -L3-L5续流；</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/bd86d4b819acd014b2de1915bda0cbceb0903526" href="https://forum.monolithicpower.cn/uploads/default/original/2X/b/bd86d4b819acd014b2de1915bda0cbceb0903526.jpeg" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/0bf67c2e3a403a33b97a5757142c0f752147b853" href="https://forum.monolithicpower.cn/uploads/default/original/2X/0/0bf67c2e3a403a33b97a5757142c0f752147b853.png" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<em>图19：VIN-SW、iL1和iL3仿真波形图及各阶段电流流向图</em>
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<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">下面同样用仿真的方式看一下L1和L4的感值对Vin-SW尖峰的影响，依旧选取四组不同的电感参数。仿真结果如下：</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/51015b98e502730f9530025311957cf0f197ee22" href="https://forum.monolithicpower.cn/uploads/default/original/2X/5/51015b98e502730f9530025311957cf0f197ee22.png" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<em>图20：不同感值下的仿真对比图</em>
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<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">由仿真结果可见L1和L4的大小都会影响上管关断时的电压应力，且感值越大，应力也会越大。</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">下面给大家分享一下不同的电压应力测试点，对实际的测试结果造成的影响。</p>
<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">当我们在实际测试下管电压应力时，由于芯片pin脚不容易点到，很多时候探头的GND会放在Cin cap的GND上，此时测量会引入寄生电感L4的影响。通过仿真波形可以看到：以Cin cap的负极为GND，SW上升沿尖峰测试会偏小，SW下降沿尖峰会偏大。</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/04b5e5aef563c6e79ebd77b5e5dd406c1dc49c82" href="https://forum.monolithicpower.cn/uploads/default/original/2X/0/04b5e5aef563c6e79ebd77b5e5dd406c1dc49c82.jpeg" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<em>图21：电压应力测试点在Cin cap的GND上</em>
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<p style="color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">当我们在测试上管电压应力时，如果探头的正极放在Cin cap的Vin上，此时测量会引入寄生电感L1的影响；通过仿真波形可知：此时测出的电压应力会比实际值偏小；</p>
<blockquote style="padding: 12px; color: rgb(74, 74, 74); text-transform: none; text-indent: 0px; letter-spacing: normal; clear: both; font-family: "DIN OT"; font-size: 16px; font-style: normal; font-weight: 400; margin-right: 0px; margin-left: 0px; word-spacing: 0px; white-space: normal; orphans: 2; widows: 2; font-variant-ligatures: normal; font-variant-caps: normal; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
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<div style="text-align: center;"><a data-download-href="https://forum.monolithicpower.cn/uploads/default/2bbc222dc51d559d406d9ed1f43c3ebf5a889022" href="https://forum.monolithicpower.cn/uploads/default/original/2X/2/2bbc222dc51d559d406d9ed1f43c3ebf5a889022.jpeg" style="transition:0.6s cubic-bezier(0.165, 0.84, 0.44, 1); overflow: hidden; cursor: pointer; background-color: rgba(0, 0, 0, 0); overflow-wrap: break-word;" title="image"></a></div>
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<em>图22：电压应力测试点在Cin cap的Vin上</em></blockquote>
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