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<div class=" wh_topic_content body "><main role="main"><article class="- topic/topic topic" role="article" aria-labelledby="ariaid-title1"><span class="edit-link" style="font-size:12px; opacity:0.6; text-align:right; vertical-align:middle"><a target="_blank" href="http://172.16.35.88/tasks/jdssno1uvvbf2mltu9kb9v3if05d5gopuakboe8hlud18rma/edit/F:/aicdita/aicdita-cn/topics/sdk/pwm/pwm_faq.dita">Edit online</a></span><h1 class="- topic/title title topictitle1" id="ariaid-title1">常见问题</h1><div class="date inPage">13 Dec 2024</div><div style="color: gray;">
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Read time: 2 minute(s)
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</div><div class="- topic/body body"><section class="- topic/section section" id="id__section_atp_kls_21c" data-ofbid="id__section_atp_kls_21c"><h2 class="- topic/title title sectiontitle">每个 PWM 控制器的两路输出信号有什么关系？</h2>
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<p class="- topic/p p" data-ofbid="d101208e22__20250121171536">每个控制器可以控制两路输出 PWM 信号，这两路信号从设计上有三个约束条件：</p>
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<ol class="- topic/ol ol" id="id__ol_btp_kls_21c" data-ofbid="id__ol_btp_kls_21c"><li class="- topic/li li" data-ofbid="d101208e26__20250121171536">
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<p class="- topic/p p" data-ofbid="d101208e28__20250121171536">共用同一个 <strong class="+ topic/ph hi-d/b ph b">time-base 信号</strong>，<span class="- topic/ph ph">即共用一路输入时钟信号，也共用了一个计数器</span></p>
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</li><li class="- topic/li li" data-ofbid="d101208e36__20250121171536">
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<p class="- topic/p p" data-ofbid="d101208e38__20250121171536">共用同一个 <strong class="+ topic/ph hi-d/b ph b">PWM 信号频率</strong> 配置参数。</p>
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</li><li class="- topic/li li" data-ofbid="d101208e44__20250121171536">
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<p class="- topic/p p" data-ofbid="d101208e46__20250121171536">共用同一个 <strong class="+ topic/ph hi-d/b ph b">占空比</strong> 配置参数。</p>
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</li></ol>
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<p class="- topic/p p" data-ofbid="d101208e53__20250121171536">上述 “PWM 信号频率” 和 “占空比” 由 PWM 的 <strong class="+ topic/ph hi-d/b ph b">调用者运行时配置</strong>。 两路信号可以完全相同，也可以做到亮点差别：</p>
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<ol class="- topic/ol ol" id="id__ol_ctp_kls_21c" data-ofbid="id__ol_ctp_kls_21c"><li class="- topic/li li" data-ofbid="d101208e60__20250121171536">
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<p class="- topic/p p" data-ofbid="d101208e62__20250121171536">相位相反，在占空比上看到的是一个为正、一个为负。</p>
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</li><li class="- topic/li li" data-ofbid="d101208e65__20250121171536">
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<p class="- topic/p p" data-ofbid="d101208e67__20250121171536">可以关闭其中一路，在 DTS 参数中将对应的 Action 配置为 “none” 即可。</p>
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</li></ol>
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</section><section class="- topic/section section" id="id__section_dtp_kls_21c" data-ofbid="id__section_dtp_kls_21c"><h2 class="- topic/title title sectiontitle">PWM 信号的占空比是反向的</h2>
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<p class="- topic/p p" data-ofbid="d101208e76__20250121171536">得到的占空比相位是反向的。比如配置 80%，得到的是 20%。</p>
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<p class="- topic/p p" data-ofbid="d101208e79__20250121171536"><strong class="+ topic/ph hi-d/b ph b">原因分析</strong></p>
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<p class="- topic/p p" data-ofbid="d101208e83__20250121171536">PWM 信号的电平跳变方向完全是由几个关键时点的配置参数决定，所以如果碰到占空比反向的情况，直接的调整方法是将配置参数反向设置即可。</p>
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<p class="- topic/p p" data-ofbid="d101208e86__20250121171536"><a xml:lang="zh-CN" lang="zh-CN" class="- topic/xref xref" href="pwm_config.html#pwm_configuration__section_mrf_pzy_gdc">pwm_config.html#pwm_configuration__section_mrf_pzy_gdc</a>
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提供了一些典型的参考配置，可以看到相邻的“负占空比”和“正占空比”参数配置基本是反向的。</p>
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</section><section class="- topic/section section" id="id__section_fpz_q1z_gdc" data-ofbid="id__section_fpz_q1z_gdc"><h2 class="- topic/title title sectiontitle">PWM 输出频率范围如何计算</h2>
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<p class="- topic/p p" data-ofbid="d101208e95__20250121171536">目前 Luban-Lite 中会根据配置的周期（单位纳秒），自动计算出最佳工作时基。本节仅描述如何计算同一时基下的最大最小频率。</p>
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<p class="- topic/p p" data-ofbid="d101208e98__20250121171536">PWM 输出频率与工作时钟频率、配置的周期以及 <code class="+ topic/ph pr-d/codeph ph codeph">action</code>信息相关。</p>
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<p class="- topic/p p" data-ofbid="d101208e104__20250121171536">工作时钟频率和父时钟、分频有关。更多时钟问题，参考 <a xml:lang="zh-CN" lang="zh-CN" class="- topic/xref xref" href="pwm_config.html#pwm_configuration__section_lhg_fyn_4dc">时钟配置</a>。</p>
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<div class="- topic/p p" data-ofbid="d101208e111__20250121171536">以 24 MHz 为例，可推导出最大最小频率：<pre class="+ topic/pre pr-d/codeblock pre codeblock language-c" id="id__codeblock_f43_hbz_gdc" data-ofbid="id__codeblock_f43_hbz_gdc">Tclk = <span class="hl-number">1</span> / fclk
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Tprd = Tclk * (prd + <span class="hl-number">1</span>)
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Tprd = (prd + <span class="hl-number">1</span>) / fclk
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fprd = fclk / (prd + <span class="hl-number">1</span>)</pre><ul class="- topic/ul ul" id="id__ul_ms2_3bz_gdc" data-ofbid="id__ul_ms2_3bz_gdc"><li class="- topic/li li" data-ofbid="d101208e116__20250121171536">
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<p class="- topic/p p" data-ofbid="d101208e118__20250121171536"><code class="+ topic/ph pr-d/codeph ph codeph">fclk</code>：工作时钟频率。</p>
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</li><li class="- topic/li li" data-ofbid="d101208e123__20250121171536">
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<p class="- topic/p p" data-ofbid="d101208e125__20250121171536"><code class="+ topic/ph pr-d/codeph ph codeph">fprd</code>：PWM 输出频率：</p>
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</li></ul></div>
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<div class="- topic/p p" data-ofbid="d101208e132__20250121171536">根据上述公式可以获得 PWM 的输出频率，如下所示：<ul class="- topic/ul ul" id="id__ul_lmy_xbz_gdc" data-ofbid="id__ul_lmy_xbz_gdc"><li class="- topic/li li" data-ofbid="d101208e135__20250121171536"><p class="- topic/p p" data-ofbid="d101208e136__20250121171536">最小频率： fprd = 24000000 / (0xFFFF + 1) ≈ 367 Hz </p><p class="- topic/p p" data-ofbid="d101208e138__20250121171536"><code class="+ topic/ph pr-d/codeph ph codeph">PRD</code>
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则可以不动作，“互补”工作交由 <code class="+ topic/ph pr-d/codeph ph codeph">ZRO</code> 与 <code class="+ topic/ph pr-d/codeph ph codeph">CMP</code>
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即可。</p><img class="- topic/image image" id="id__image_gsx_gcz_gdd" src="../../../images/sdk/minfreq.png" alt="mminfreq"/>
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</li><li class="- topic/li li" data-ofbid="d101208e152__20250121171536"><p class="- topic/p p" data-ofbid="d101208e153__20250121171536">最大频率： fprd = 24000000 / (1 + 1) = 12 MHz</p><p class="- topic/p p" data-ofbid="d101208e155__20250121171536">当 <code class="+ topic/ph pr-d/codeph ph codeph">prd 寄存器</code>
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设置为 1 （最小为 1 ）时，<code class="+ topic/ph pr-d/codeph ph codeph">action</code>
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<code class="+ topic/ph pr-d/codeph ph codeph">CMP</code> 部分应配置为不动作，<code class="+ topic/ph pr-d/codeph ph codeph">PRD</code> 与
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<code class="+ topic/ph pr-d/codeph ph codeph">ZRO</code> 互补高低电平，即可输出 12 MHz。</p><img class="- topic/image image" id="id__image_gsx_gcz_gdc" src="../../../images/sdk/maxfreq.png" alt="maxfreq"/></li></ul></div>
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<div class="- topic/div div">
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<p class="- topic/p p" data-ofbid="d101208e180__20250121171536">最大频率可与最小频率、正常输出频率时一样，只配置 <code class="+ topic/ph pr-d/codeph ph codeph">CMP</code> 与 <code class="+ topic/ph pr-d/codeph ph codeph">ZRO</code> 动作，
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<code class="+ topic/ph pr-d/codeph ph codeph">PRD</code> 不动作，此时配置 <code class="+ topic/ph pr-d/codeph ph codeph">cmp 寄存器</code> 与
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<code class="+ topic/ph pr-d/codeph ph codeph">prd 寄存器</code> 相等理论上能产生一样的效果。但由于驱动中默认设计当 <code class="+ topic/ph pr-d/codeph ph codeph">cmp 寄存器</code> 与
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<code class="+ topic/ph pr-d/codeph ph codeph">prd 寄存器</code> 相等时，为了输出 100% 占空比，<code class="+ topic/ph pr-d/codeph ph codeph">cmp 寄存器</code> 会默认增加
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1。这个问题我们在下章节毛刺问题作出解析。</p>
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<div class=" wh_topic_toc "><div class="wh_topic_label">在本页上</div><ul><li class="section-item"><div class="section-title"><a href="#id__section_atp_kls_21c" data-tocid="id__section_atp_kls_21c">每个 PWM 控制器的两路输出信号有什么关系？</a></div></li><li class="section-item"><div class="section-title"><a href="#id__section_dtp_kls_21c" data-tocid="id__section_dtp_kls_21c">PWM 信号的占空比是反向的</a></div></li><li class="section-item"><div class="section-title"><a href="#id__section_fpz_q1z_gdc" data-tocid="id__section_fpz_q1z_gdc">PWM 输出频率范围如何计算</a></div></li></ul></div>
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