無論是(shi)做什(shen)么用途，或(huo)制(zhi)造商是(shi)誰，手持式電(dian)(dian)子設(she)備都有(you)一(yi)(yi)個共同的(de)(de)特性：一(yi)(yi)個可充電(dian)(dian)的(de)(de)電(dian)(dian)池(chi)，多數情(qing)況下還有(you)一(yi)(yi)個內(nei)建(jian)的(de)(de)充電(dian)(dian)電(dian)(dian)路(lu)(lu)。當(dang)一(yi)(yi)個AC適配器這(zhe)樣的(de)(de)外部電(dian)(dian)源(yuan)(yuan)(yuan)或(huo)一(yi)(yi)個USB端口接到手持設(she)備的(de)(de)輸入端，充電(dian)(dian)電(dian)(dian)路(lu)(lu)將對電(dian)(dian)池(chi)充電(dian)(dian)。當(dang)接到外部電(dian)(dian)源(yuan)(yuan)(yuan)時，如(ru)果設(she)備正處在(zai)開機狀態，理想的(de)(de)情(qing)形是(shi)，設(she)備應當(dang)從(cong)外部電(dian)(dian)源(yuan)(yuan)(yuan)汲取盡可能多的(de)(de)功(gong)率，以節(jie)省電(dian)(dian)池(chi)壽(shou)命。要實現這(zhe)個功(gong)能則需要一(yi)(yi)個自動的(de)(de)電(dian)(dian)源(yuan)(yuan)(yuan)選擇電(dian)(dian)路(lu)(lu)，這(zhe)個電(dian)(dian)路(lu)(lu)通常是(shi)集成(cheng)在(zai)充電(dian)(dian)控(kong)制(zhi)IC內(nei)。設(she)計(ji)者可以從(cong)動態或(huo)靜態電(dian)(dian)源(yuan)(yuan)(yuan)路(lu)(lu)徑(jing)管理當(dang)中選擇其(qi)中的(de)(de)一(yi)(yi)種，進(jin)行電(dian)(dian)源(yuan)(yuan)(yuan)管理。

　　在電(dian)(dian)(dian)(dian)(dian)池(chi)供電(dian)(dian)(dian)(dian)(dian)的(de)(de)手持(chi)設(she)備中，動(dong)態電(dian)(dian)(dian)(dian)(dian)源路(lu)徑管理(DPPM)是更流行的(de)(de)機(ji)制。DPPM功能框圖如圖1所(suo)(suo)示。主通路(lu)元(yuan)件QMAIN是一(yi)個(ge)(ge)電(dian)(dian)(dian)(dian)(dian)壓穩壓器，提供一(yi)個(ge)(ge)經(jing)過(guo)穩壓的(de)(de)輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)壓VOUT。第(di)二(er)個(ge)(ge)通路(lu)元(yuan)件QCharge是充電(dian)(dian)(dian)(dian)(dian)控(kong)制元(yuan)件，由VOUT供電(dian)(dian)(dian)(dian)(dian)，提供恒定的(de)(de)電(dian)(dian)(dian)(dian)(dian)流或(huo)恒定的(de)(de)電(dian)(dian)(dian)(dian)(dian)壓對電(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)。在充電(dian)(dian)(dian)(dian)(dian)期(qi)間，如果輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)流超(chao)過(guo)電(dian)(dian)(dian)(dian)(dian)源的(de)(de)電(dian)(dian)(dian)(dian)(dian)流限值，QCharge就會變成一(yi)個(ge)(ge)開關，將(jiang)電(dian)(dian)(dian)(dian)(dian)池(chi)連到系統上，提供一(yi)部分所(suo)(suo)需(xu)的(de)(de)輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)流。

　　DPPM有(you)幾個(ge)好處。首先，當(dang)(dang)(dang)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)完全放電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)(電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)耗(hao)盡(jin)的(de)(de)情況)，DPPM能(neng)讓外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)立(li)刻(ke)給設備供電(dian)(dian)(dian)(dian)(dian)(dian)。如(ru)果沒有(you)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)路(lu)徑(jing)(jing)管理，在電(dian)(dian)(dian)(dian)(dian)(dian)量耗(hao)盡(jin)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)被充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)到(dao)(dao)(dao)系(xi)(xi)(xi)統(tong)能(neng)夠啟動的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓等(deng)(deng)級(ji)之前(一(yi)般是高于3V)，系(xi)(xi)(xi)統(tong)是無法上(shang)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)。這(zhe)個(ge)等(deng)(deng)待周期取決(jue)于充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)的(de)(de)涓流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)設定，可能(neng)是幾分鐘到(dao)(dao)(dao)十分鐘的(de)(de)時(shi)(shi)間。其次，當(dang)(dang)(dang)用外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)對電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)，DPPM會(hui)把來自(zi)外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)分到(dao)(dao)(dao)兩(liang)個(ge)路(lu)徑(jing)(jing)中(zhong)，一(yi)條(tiao)路(lu)徑(jing)(jing)為(wei)手持設備提(ti)供必(bi)要(yao)的(de)(de)功率，另一(yi)條(tiao)路(lu)徑(jing)(jing)輸出充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，來給電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。當(dang)(dang)(dang)外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)輸入電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)達(da)到(dao)(dao)(dao)限值時(shi)(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)路(lu)徑(jing)(jing)管理會(hui)對輸入到(dao)(dao)(dao)手持系(xi)(xi)(xi)統(tong)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)進(jin)行優(you)先級(ji)分類。這(zhe)樣如(ru)果當(dang)(dang)(dang)系(xi)(xi)(xi)統(tong)工作時(shi)(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)正在充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)可以在最(zui)短的(de)(de)時(shi)(shi)間內充(chong)(chong)(chong)滿，因為(wei)動態控制的(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)是為(wei)這(zhe)個(ge)目標而優(you)化的(de)(de)。當(dang)(dang)(dang)外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)被移(yi)走時(shi)(shi)，QCharge立(li)刻(ke)完全打開，把電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)連到(dao)(dao)(dao)系(xi)(xi)(xi)統(tong)上(shang)，向系(xi)(xi)(xi)統(tong)輸出所需的(de)(de)全部(bu)功率。

　　圖1，動(dong)態電源路徑(jing)管理框(kuang)圖

　　但DPPM機制有一些限制。第一種情況是，當系統電流發生快速瞬變時，電壓會下降。這種情況如果發生在電池充電期間，如果系統電流處在突發方式下，輸出端的負載電流會周期性地迅速從接近零升高到2A以上。由于這個電流超過了輸入電源的最大容量，充電FET不得不將電流反向，提供一部分的突發電流。由于電流反向需要一定的時間，在這段時間內，輸出電壓會降低，導致電流產生畸變，如圖2所示。第二各限制條件是IC設計的成本和復雜度，因為由兩個通路元件需要調節。一個元件調節到系統的輸出電壓，另一個調節對電池充電的電壓或電流。

　　圖2，靜態電源路徑管理(li)的瞬態電流響應(ying)

　　靜態電源路徑管路

　　靜態電源路徑管理(SPPM)是一(yi)個(ge)簡化(hua)的解(jie)決(jue)(jue)辦法，能達到上面提到的第一(yi)個(ge)目標，不(bu)會出現電(dian)壓下降的情況。然而(er)，它(ta)沒法解(jie)決(jue)(jue)第二個(ge)問(wen)題，即區分系統(tong)和充電(dian)電(dian)流的優先級。

　　SPPM機(ji)制(zhi)(zhi)的(de)概念(nian)如圖3所(suo)(suo)示。主FET QMAIN是(shi)充電(dian)(dian)控制(zhi)(zhi)器(qi)元件。開關SW1連接電(dian)(dian)池和系(xi)統(tong)。當電(dian)(dian)池電(dian)(dian)壓高于VPPM閾(yu)值(系(xi)統(tong)的(de)最小工作電(dian)(dian)壓，一般是(shi)3.2V)，開關導通，無論外(wai)部電(dian)(dian)源存在與(yu)否(fou)，電(dian)(dian)池都(dou)會連到(dao)系(xi)統(tong)。這樣，當系(xi)統(tong)突(tu)然汲取電(dian)(dian)流(liu)時(shi)，由(you)于開關已經處在導通狀態(tai)，電(dian)(dian)池能夠隨(sui)時(shi)提供系(xi)統(tong)所(suo)(suo)需(xu)的(de)電(dian)(dian)流(liu)。這樣就解決(jue)了電(dian)(dian)壓降(jiang)和電(dian)(dian)流(liu)畸(ji)變問題，如圖5所(suo)(suo)示。由(you)于在設計中(zhong)僅(jin)需(xu)要一個(ge)調整元件對電(dian)(dian)池的(de)充電(dian)(dian)電(dian)(dian)壓或電(dian)(dian)流(liu)進行(xing)調節，IC設計成本和復雜(za)度(du)也(ye)降(jiang)低了。如果需(xu)要極低阻抗(kang)的(de)開關，圖3中(zhong)的(de)開關SW1可(ke)以放到(dao)IC外(wai)面來實現，進一步(bu)降(jiang)低成本。

　　如果電(dian)池(chi)電(dian)壓低于VPPM的閾值，SW1就(jiu)開啟(qi)(qi)，VOUT將(jiang)變成4.2V的恒(heng)壓源(yuan)，向系統供電(dian)。與此(ci)同時，50mA的恒(heng)流(liu)(liu)源(yuan)ITRKL被(bei)激活(huo)，在(zai)涓(juan)流(liu)(liu)模式下對(dui)電(dian)池(chi)充電(dian)，直到電(dian)壓達到VPPM閾值(有一定滯后(hou))，然(ran)后(hou)SW1會關閉，電(dian)池(chi)就(jiu)連到系統上。這樣就(jiu)解決(jue)了(le)沒電(dian)電(dian)池(chi)的啟(qi)(qi)動(dong)問(wen)題。

　　由于SPPM解決在電池沒電情況下的系統啟動問題，對于手持式應用來說，這是一種很有吸引力的電池充電器解決方案。

　　圖3，靜態電(dian)源路徑管理框圖

　　圖4，靜(jing)態電(dian)源(yuan)路徑管(guan)理控制(zhi)流(liu)程

　　圖5，靜(jing)態電源(yuan)路徑管理(li)的瞬態電流響應