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<div class="WordSection1"> <h1>DCR溫度補償</h1> <p><br></p> <h2 id="__Bookmark__0">摘要</h2> <p>DCR電流檢測技術,因其具有無損耗之優點,是一個能獲得正確電感電流訊息的好方法。然而,金屬銅本身具有正溫度係數,所以電感的 DCR 值會隨溫度變化而改變。而隨溫度變化的DCR 值,就會使控制器檢測到不正確的電流信號。 常用的解決方式是在電流檢測迴路中加上 DCR 溫度網路,以避免此溫度效應。故此,本應用須知將介紹 DCR 溫度補償的基本概念和電路實現的方法。</p> <p class="MsoNormal"><br><br></p> <h2 id="__Bookmark__1">1.為何需要DCR溫度補償網路</h2> <p>圖一所示為一 DCR 電流檢測網路。當時間常數相等,也就是 C<sub>x</sub>R<sub>x</sub> = L / DCR 時,如式(1)所示,V<sub>CX</sub>電壓可用來取得電感電流信號。然而, DCR 值會以正比隨溫度增加,如式(2)所示,其中參數 TC<sub>DCR</sub> 是銅的溫度係數,且是一正數。當電路在重載條件下工作時,電感的溫度也會隨之增加。這使得穩壓器會因隨溫度改變的 DCR 值,檢測到錯誤的負載電流值,進而回報不正確的電流訊息。此外,也會使得輸出電壓無法達到其該有的值,也因此就無法滿足在 V<sub>CORE</sub> 應用中所需要的適應性電壓定位 (AVP) 下垂的負載線規格。所以,在此探討的溫度補償網路就是為了解決這個問題。</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image001_zh-tw.jpg"> <img id="圖片 1" alt="Technical Document Image Preview" height="46" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image001_zh-tw.jpg" width="321"></a></p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image002_zh-tw.jpg"> <img id="圖片 3" alt="Technical Document Image Preview" height="138" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image002_zh-tw.jpg" width="234"></a></p> <p class="MsoNormal">圖一、DCR電流檢測網路</p> <p class="MsoNormal"><br><br></p> <h2 id="__Bookmark__2">2. DCR 溫度補償之架構</h2> <p>DCR溫度補償網路的目的就是使 DCR 值不隨溫度改變,因此使得 V<sub>CX</sub> 電壓只和電感電流有關。因為 DCR 是一具有正溫度係數的電阻,所以就必須在電流檢測迴路中插入一個有負溫度係數的電阻性網路,以補償 DCR 隨溫度的變化。當有 Y個溫度點需要進行補償,補償網路就需要 Y 個電阻和一個負溫度係數(NTC)的熱敏電阻,如此才能在這 Y 個溫度點時,DCR 值的溫度變化均可被抵消。然而,不同的電流檢測架構,DCR溫度補償網路的設計方式也不同。圖二和圖三分別顯示了總和電流檢測架構 (sum current sensing topology) 和差分電流檢測架構 (differential current sensing topology) 的溫度補償網路,及其電路示意圖。總和電流檢測架構示範的是有三個溫度點作補償的補償網路,而差分電流檢測架構則示範的是有兩個溫度點作補償的補償網路。式(3)和式(4)可分別作為這兩個電流檢測架構的設計原則。</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image003_zh-tw.jpg"> <img id="圖片 8" alt="Technical Document Image Preview" height="87" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image003_zh-tw.jpg" width="344"></a></p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image004_zh-tw.jpg"> <img id="圖片 9" alt="Technical Document Image Preview" height="470" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image004_zh-tw.jpg" width="658"></a></p> <p class="MsoNormal">圖二、總和電流檢測架構之DCR溫度補償網路</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image005_zh-tw.jpg"> <img id="圖片 10" alt="Technical Document Image Preview" height="547" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image005_zh-tw.jpg" width="672"></a></p> <p class="MsoNormal">圖三、差分電流檢測架構之DCR溫度補償網路</p> <p class="MsoNormal"><br><br></p> <h2 id="__Bookmark__3">3. DCR 溫度補償網路之公式推導</h2> <p>在本節中,將以總和電流檢測架構為例,說明如何推導出溫度補償網路。如式(3),藉由 V<sub>sum</sub> 電壓及一個適當的比例,即可得到正確負載電流的訊息;此比例為R<sub>sum</sub> 和(R<sub>x</sub>+R<sub>s</sub>)之比,如式 (5)所示。以 RT8893 例,此值必須設為4,才能有正常的操作。</p> <p> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image006_zh-tw.jpg"> <img id="圖片 12" alt="Technical Document Image Preview" height="41" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image006_zh-tw.jpg" width="233"></a></p> <p>而為了消除溫度對 DCR 的影響,必須在 R<sub>sum</sub> 網路中插入一個 NTC 熱敏電阻,使得 V<sub>sum</sub> 電壓不會隨溫度改變。 NTC熱敏電阻和溫度之間的關係如式(6),其中 &beta; 是 NTC 的溫度係數;不同的 NTC 熱敏電阻,&beta; 值也會不同。</p> <p> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image007_zh-tw.jpg"> <img id="圖片 13" alt="Technical Document Image Preview" height="37" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image007_zh-tw.jpg" width="286"></a></p> <p>如果是有三個溫度點(TL、TR和TH)需要進行補償,則在此三個溫度點,V<sub>sum</sub> 電壓必須相同;也就是如式(7)之右側所示之結果,與溫度無關。R<sub>sum</sub>(T) 為內含 NTC 熱敏電阻的熱補償網路之等效電阻,其表示式為式(8)。</p> <p> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image008_zh-tw.jpg"> <img id="圖片 14" alt="Technical Document Image Preview" height="96" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image008_zh-tw.jpg" width="348"></a></p> <p>因此,由以上公式,R<sub>sum</sub> 網路之各參數可分別由公式(9),(10),和(11)得出。詳細之推導,可參閱附錄 I。</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image009_zh-tw.jpg"> <img id="圖片 15" alt="Technical Document Image Preview" height="123" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image009_zh-tw.jpg" width="348"></a></p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image010_zh-tw.jpg"> <img id="圖片 16" alt="Technical Document Image Preview" height="77" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image010_zh-tw.jpg" width="566"></a></p> <p>在經過溫度補償電路之後,V<sub>SUM</sub> 在這三個溫度點的誤差(例如:20&deg;C, 60&deg;C, 和 100&deg;C)應當為零,如圖四所示。</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image011_zh-tw.jpg"> <img id="圖片 11" alt="Technical Document Image Preview" height="455" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image011_zh-tw.jpg" width="680"></a></p> <p class="MsoNormal">圖四、DCR溫度補償後之V<sub>SUM</sub>誤差</p> <p class="MsoNormal"><br><br></p> <h2 id="__Bookmark__4">4. DCR 溫度補償網路的設計範例</h2> <p>以下設計方法所選用的是總和電流檢測架構,並以 RT8893 作為設計範例;所訂的規格是根據英特爾VR12.5的設計需求。</p> <div> <table border="1" cellpadding="0" cellspacing="0" class="MsoTableLightListAccent5" style="width: 40.24%; border-collapse: collapse; border: none" width="40%"> <tr> <td colspan="2" style="width: 100.0%; border: solid #4BACC6 1.0pt; border-bottom: none; background: #4BACC6; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="100%"> <p class="MsoNormal">VCORE 規格</p> </td> </tr> <tr> <td style="width: 62.16%; border: solid #4BACC6 1.0pt; border-right: solid #009EB8 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="62%"> <p class="MsoNormal">輸入電壓</p> </td> <td style="width: 37.84%; border: solid #4BACC6 1.0pt; border-left: none; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="37%"> <p class="MsoNormal">10.8V to 13.2V</p> </td> </tr> <tr> <td style="width: 62.16%; border-top: none; border-left: solid #4BACC6 1.0pt; border-bottom: none; border-right: solid #009EB8 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="62%"> <p class="MsoNormal">相位數</p> </td> <td style="width: 37.84%; border: none; border-right: solid #4BACC6 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="37%"> <p class="MsoNormal">3</p> </td> </tr> <tr> <td style="width: 62.16%; border: solid #4BACC6 1.0pt; border-right: solid #009EB8 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="62%"> <p class="MsoNormal">Vboot</p> </td> <td style="width: 37.84%; border: solid #4BACC6 1.0pt; border-left: none; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="37%"> <p class="MsoNormal">1.7V</p> </td> </tr> <tr> <td style="width: 62.16%; border-top: none; border-left: solid #4BACC6 1.0pt; border-bottom: none; border-right: solid #009EB8 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="62%"> <p class="MsoNormal">VDAC(MAX)</p> </td> <td style="width: 37.84%; border: none; border-right: solid #4BACC6 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="37%"> <p class="MsoNormal">1.8V</p> </td> </tr> <tr> <td style="width: 62.16%; border: solid #4BACC6 1.0pt; border-right: solid #009EB8 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="62%"> <p class="MsoNormal">ICCMAX</p> </td> <td style="width: 37.84%; border: solid #4BACC6 1.0pt; border-left: none; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="37%"> <p class="MsoNormal">90A</p> </td> </tr> <tr> <td style="width: 62.16%; border-top: none; border-left: solid #4BACC6 1.0pt; border-bottom: none; border-right: solid #009EB8 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="62%"> <p class="MsoNormal">ICC-DY</p> </td> <td style="width: 37.84%; border: none; border-right: solid #4BACC6 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="37%"> <p class="MsoNormal">60A</p> </td> </tr> <tr> <td style="width: 62.16%; border: solid #4BACC6 1.0pt; border-right: solid #009EB8 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="62%"> <p class="MsoNormal">ICC-TDC</p> </td> <td style="width: 37.84%; border: solid #4BACC6 1.0pt; border-left: none; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="37%"> <p class="MsoNormal">55A</p> </td> </tr> <tr> <td style="width: 62.16%; border-top: none; border-left: solid #4BACC6 1.0pt; border-bottom: none; border-right: solid #009EB8 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="62%"> <p class="MsoNormal">負載線</p> </td> <td style="width: 37.84%; border: none; border-right: solid #4BACC6 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="37%"> <p class="MsoNormal">1.5m&Omega;</p> </td> </tr> <tr> <td style="width: 62.16%; border: solid #4BACC6 1.0pt; border-right: solid #009EB8 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="62%"> <p class="MsoNormal">快速電壓迴轉率</p> </td> <td style="width: 37.84%; border: solid #4BACC6 1.0pt; border-left: none; padding: 0cm 5.4pt 0cm 5.4pt" valign="top" width="37%"> <p class="MsoNormal">12.5mV/&micro;s</p> </td> </tr> <tr style="height: 13.5pt"> <td style="width: 62.16%; border-top: none; border-left: solid #4BACC6 1.0pt; border-bottom: solid #4BACC6 1.0pt; border-right: solid #009EB8 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 13.5pt" valign="top" width="62%"> <p class="MsoNormal">最大開關頻率</p> </td> <td style="width: 37.84%; border-top: none; border-left: none; border-bottom: solid #4BACC6 1.0pt; border-right: solid #4BACC6 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 13.5pt" valign="top" width="37%"> <p class="MsoNormal">300kHz</p> </td> </tr> </table> </div> <p>在 Shark Bay VRTB 桌上型平台指南中,輸出濾波器的設計需求如下所示:</p> <p>輸出電感:360nH/0.72m&Omega; <br>輸出大型電容:560&micro;F/2.5V/5m&Omega;(max) 4 至 5 個<br>輸出陶瓷電容:22&micro;F / 0805 (在上層最多可放 18 個) <br><br></p> <p>步驟1:決定電感的參數</p> <p>決定電感值。<br>輸出電感:360nH/0.72m&Omega;<br>決定DCR溫度係數,TC<sub>DCR</sub>。<br>TC<sub>DCR</sub> = 3930ppm <br>因此,受溫度影響的電感 DCR值,可由式(2)算出。下面的計算範例是 60&deg;C 的 DCR 值。</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image012_zh-tw.jpg"> <img id="圖片 21" alt="Technical Document Image Preview" height="33" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image012_zh-tw.jpg" width="365"></a><br> <br></p> <p>步驟2:決定熱補償的NTC參數</p> <p>選用型號 NCP15WL104J03RC 的 NTC熱敏電阻;該電阻值為100k&Omega;,且 &beta; 值是 4485。利用式(6),可以計算在不同溫度下的 NTC 電阻值;NTC熱敏電阻操作於 60&deg;C 時,其電阻值可計算如下:</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image013_zh-tw.jpg"> <img id="圖片 22" alt="Technical Document Image Preview" height="35" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image013_zh-tw.jpg" width="300"></a><br> <br></p> <p>步驟3:設計 DCR 電流檢測網路及 R<sub>x</sub>、R<sub>s</sub> 和 R<sub>sum</sub> 之值</p> <p>如何決定 DCR 電流檢測網路中之電容 C<sub>x</sub> 及電阻 R<sub>X</sub> 和 R<sub>S</sub> ,可參閱應用須知AN033 「不同DCR電流檢測架構之比較」。<br>C<sub>x</sub> = 1&micro;F, R<sub>s</sub> = 3.41k&Omega;, and R<sub>x</sub> = 590&Omega; <br>在RT8893,R<sub>sum</sub> 和 (R<sub>x</sub>+R<sub>s</sub>) 之比值必須設為4,才能有正常的操作。<br>R<sub>sum</sub> = 4&#8226;(R<sub>x</sub>+R<sub>s</sub>) = 16k&Omega; <br><br></p> <p>步驟4:設計R<sub>sum</sub> 之電阻網路</p> <p>選定三個作溫度補償之溫度點。<br>選擇(TH,TR,TL)=(100,60,20)<br>例如,R<sub>sum</sub> 在 60&deg;C 下的值可由式(7)獲得:</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image014_zh-tw.jpg"> <img id="圖片 17" alt="Technical Document Image Preview" height="41" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image014_zh-tw.jpg" width="372"></a></p> <p>因此,參數&alpha;<sub>1</sub>,&alpha;<sub>2</sub>,及&Kappa;<sub>R</sub>可以計算如下:</p> <p> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image015_zh-tw.jpg"> <img id="圖片 19" alt="Technical Document Image Preview" height="171" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image015_zh-tw.jpg" width="405"></a></p> <p class="MsoNormal">再藉由公式(9),(10),和(11),可因此而算出R<sub>sump</sub>,R<sub>sums2</sub>和R<sub>sums1</sub>。</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image016_zh-tw.jpg"> <img id="圖片 24" alt="Technical Document Image Preview" height="125" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image016_zh-tw.jpg" width="386"></a></p> <p class="MsoNormal"><br><br></p> <h2 id="__Bookmark__5">5. 實驗結果</h2> <p>圖五顯示了有 DCR 溫度補償之 DCLL 和 DIMON 回報結果。從實驗結果來看,DCLL和DIMON回報結果都在容忍範圍內。然而,若無 DCR 溫度補償,則在重載條件下,DIMON 回報結果會是高估的,因而造成 DCLL 會無法滿足負載線規格,見圖六。</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image017_zh-tw.gif"> <img id="圖片 50" alt="Technical Document Image Preview" height="262" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image017_zh-tw.gif" width="415"></a></p> <p class="MsoNormal">(a) DCLL </p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image018_zh-tw.jpg"> <img id="圖片 51" alt="Technical Document Image Preview" height="250" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image018_zh-tw.jpg" width="399"></a></p> <p class="MsoNormal">(b)DIMON 回報<br>圖五、有 DCR 溫度補償之 DCLL 和 DIMON 回報結果</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image019_zh-tw.jpg"> <img id="圖片 52" alt="Technical Document Image Preview" height="255" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image019_zh-tw.jpg" width="407"></a></p> <p class="MsoNormal">(a) DCLL </p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image020_zh-tw.jpg"> <img id="圖片 53" alt="Technical Document Image Preview" height="257" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image020_zh-tw.jpg" width="410"></a></p> <p class="MsoNormal">(b)DIMON 回報<br>圖六、無DCR溫度補償之 DCLL 和 DIMON 報告結果<br><br> </p> <h2 id="__Bookmark__6">6. 結論</h2> <p>本應用須知提供了DCR溫度補償電路的設計方法及實用的設計公式;經由適當的設計,它可以有效地減少因溫度變化而對 DCR 值產生的影響,因此能在 DCR 電流檢測應用中,提供正確的電流訊息。</p> <p class="MsoNormal"><br><br></p> <h2 id="__Bookmark__7">7. 參考資料</h2> <p>[1] 立錡科技 RT8884B 規格書。<br>[2] 立錡科技 RT8893 規格書。<br>[3] Intel, VR12.5 Pulse Width Modulation (PWM) 規格<br>[4] 立錡科技之應用須知AN033 「不同DCR電流檢測架構之比較」。</p> <p class="MsoNormal"><br><br></p> <h2 id="__Bookmark__8">附錄I. DCR溫度補償網路之公式推導</h2> <p>將三個溫度點(TL,TR,TH)都代入式(8),即可得式(12)至式(14)。而式(15)和式(16)可分別由式(12)- 式(13)和式(13)- 式(14)得出。</p> <p> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image021_zh-tw.jpg"> <img id="圖片 25" alt="Technical Document Image Preview" height="311" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image021_zh-tw.jpg" width="506"></a></p> <p>定義 k<sub>R</sub>=R<sub>sump</sub>+R<sub>sums2</sub>,則可進一步將式(15)和式(16)表示為式(17)和式(18)。</p> <p> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image022_zh-tw.jpg"> <img id="圖片 26" alt="Technical Document Image Preview" height="272" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image022_zh-tw.jpg" width="619"></a></p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image023_zh-tw.jpg"> <img id="圖片 27" alt="Technical Document Image Preview" height="274" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image023_zh-tw.jpg" width="631"></a></p> <p>式(19)可由式(18)/ 式(17)導出。</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image024_zh-tw.jpg"> <img id="圖片 28" alt="Technical Document Image Preview" height="170" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image024_zh-tw.jpg" width="469"></a></p> <p>從式(18),可得R<sub>sump</sub>,如式(20)。</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image025_zh-tw.jpg"> <img id="圖片 29" alt="Technical Document Image Preview" height="61" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image025_zh-tw.jpg" width="471"></a></p> <p>然後,可得 R<sub>sums2</sub>,如式(21)。</p> <p> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image026_zh-tw.jpg"> <img id="圖片 30" alt="Technical Document Image Preview" height="71" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image026_zh-tw.jpg" width="467"></a></p> <p>R<sub>sums1</sub>可因此推導而得,如式(22)。</p> <p class="MsoNormal"> <a class="fancybox" href="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image027_zh-tw.jpg"> <img id="圖片 31" alt="Technical Document Image Preview" height="113" src="/content/dam/richtek-eds/resources/application-notes/an026/html-images-zh_tw/image027_zh-tw.jpg" width="466"></a></p> <p class="MsoNormal"><br><br></p> <div> <table border="1" cellspacing="0" cellpadding="0" style="width: 637.5pt; 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