無(wu)論是(shi)做什么用途，或(huo)制造(zao)商是(shi)誰(shui)，手(shou)持式電(dian)(dian)子設備(bei)都有(you)一(yi)個(ge)共(gong)同的特(te)性：一(yi)個(ge)可充(chong)電(dian)(dian)的電(dian)(dian)池，多(duo)(duo)數情(qing)況(kuang)下還有(you)一(yi)個(ge)內建(jian)的充(chong)電(dian)(dian)電(dian)(dian)路(lu)。當一(yi)個(ge)AC適配(pei)器這(zhe)(zhe)樣的外部電(dian)(dian)源(yuan)或(huo)一(yi)個(ge)USB端口接到手(shou)持設備(bei)的輸入端，充(chong)電(dian)(dian)電(dian)(dian)路(lu)將對電(dian)(dian)池充(chong)電(dian)(dian)。當接到外部電(dian)(dian)源(yuan)時，如果設備(bei)正處在(zai)開(kai)機狀態，理想的情(qing)形是(shi)，設備(bei)應當從外部電(dian)(dian)源(yuan)汲取盡可能(neng)(neng)多(duo)(duo)的功(gong)率(lv)，以節(jie)省電(dian)(dian)池壽(shou)命。要(yao)實(shi)現這(zhe)(zhe)個(ge)功(gong)能(neng)(neng)則(ze)需要(yao)一(yi)個(ge)自動的電(dian)(dian)源(yuan)選擇電(dian)(dian)路(lu)，這(zhe)(zhe)個(ge)電(dian)(dian)路(lu)通(tong)常是(shi)集成在(zai)充(chong)電(dian)(dian)控制IC內。設計者可以從動態或(huo)靜態電(dian)(dian)源(yuan)路(lu)徑管理當中選擇其中的一(yi)種，進行電(dian)(dian)源(yuan)管理。

　　在電(dian)(dian)(dian)(dian)(dian)池(chi)供(gong)(gong)電(dian)(dian)(dian)(dian)(dian)的(de)手持設備中，動態電(dian)(dian)(dian)(dian)(dian)源路徑管理(DPPM)是更流行的(de)機制(zhi)。DPPM功能框圖如圖1所示。主通路元(yuan)件QMAIN是一個(ge)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)穩壓(ya)(ya)器，提(ti)(ti)供(gong)(gong)一個(ge)經過穩壓(ya)(ya)的(de)輸出(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)VOUT。第(di)二(er)個(ge)通路元(yuan)件QCharge是充(chong)電(dian)(dian)(dian)(dian)(dian)控制(zhi)元(yuan)件，由(you)VOUT供(gong)(gong)電(dian)(dian)(dian)(dian)(dian)，提(ti)(ti)供(gong)(gong)恒(heng)定的(de)電(dian)(dian)(dian)(dian)(dian)流或(huo)恒(heng)定的(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)對(dui)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)。在充(chong)電(dian)(dian)(dian)(dian)(dian)期間(jian)，如果(guo)輸出(chu)電(dian)(dian)(dian)(dian)(dian)流超(chao)過電(dian)(dian)(dian)(dian)(dian)源的(de)電(dian)(dian)(dian)(dian)(dian)流限值，QCharge就會變成一個(ge)開關，將電(dian)(dian)(dian)(dian)(dian)池(chi)連到系(xi)統上(shang)，提(ti)(ti)供(gong)(gong)一部分(fen)所需的(de)輸出(chu)電(dian)(dian)(dian)(dian)(dian)流。

　　DPPM有幾(ji)個(ge)(ge)好(hao)處。首先，當(dang)電(dian)(dian)(dian)池(chi)完全(quan)放(fang)電(dian)(dian)(dian)時(shi)(shi)(電(dian)(dian)(dian)池(chi)耗(hao)盡(jin)的(de)(de)情況)，DPPM能讓(rang)外(wai)部(bu)電(dian)(dian)(dian)源立刻給(gei)設(she)備供(gong)電(dian)(dian)(dian)。如果沒有電(dian)(dian)(dian)源路(lu)徑管理(li)(li)，在電(dian)(dian)(dian)量耗(hao)盡(jin)的(de)(de)電(dian)(dian)(dian)池(chi)被充(chong)(chong)電(dian)(dian)(dian)到系(xi)(xi)(xi)統(tong)能夠(gou)啟動的(de)(de)電(dian)(dian)(dian)壓等級之前(一般(ban)是(shi)高于3V)，系(xi)(xi)(xi)統(tong)是(shi)無法上電(dian)(dian)(dian)的(de)(de)。這個(ge)(ge)等待(dai)周期取決于充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)路(lu)的(de)(de)涓流(liu)(liu)充(chong)(chong)電(dian)(dian)(dian)設(she)定，可能是(shi)幾(ji)分(fen)鐘(zhong)到十分(fen)鐘(zhong)的(de)(de)時(shi)(shi)間。其次，當(dang)用外(wai)部(bu)電(dian)(dian)(dian)源對電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)時(shi)(shi)，DPPM會(hui)把來自(zi)外(wai)部(bu)電(dian)(dian)(dian)源的(de)(de)電(dian)(dian)(dian)流(liu)(liu)分(fen)到兩個(ge)(ge)路(lu)徑中，一條路(lu)徑為(wei)(wei)(wei)手(shou)持設(she)備提(ti)供(gong)必要的(de)(de)功(gong)率(lv)，另一條路(lu)徑輸出充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)，來給(gei)電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)。當(dang)外(wai)部(bu)電(dian)(dian)(dian)源的(de)(de)輸入電(dian)(dian)(dian)流(liu)(liu)達到限值(zhi)時(shi)(shi)，電(dian)(dian)(dian)源路(lu)徑管理(li)(li)會(hui)對輸入到手(shou)持系(xi)(xi)(xi)統(tong)的(de)(de)電(dian)(dian)(dian)流(liu)(liu)進(jin)行優先級分(fen)類。這樣如果當(dang)系(xi)(xi)(xi)統(tong)工作時(shi)(shi)，電(dian)(dian)(dian)池(chi)正在充(chong)(chong)電(dian)(dian)(dian)，電(dian)(dian)(dian)池(chi)可以在最短的(de)(de)時(shi)(shi)間內充(chong)(chong)滿，因為(wei)(wei)(wei)動態控(kong)制的(de)(de)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)是(shi)為(wei)(wei)(wei)這個(ge)(ge)目標而優化的(de)(de)。當(dang)外(wai)部(bu)電(dian)(dian)(dian)源被移走時(shi)(shi)，QCharge立刻完全(quan)打開，把電(dian)(dian)(dian)池(chi)連到系(xi)(xi)(xi)統(tong)上，向系(xi)(xi)(xi)統(tong)輸出所需的(de)(de)全(quan)部(bu)功(gong)率(lv)。

　　圖1，動態電源路徑(jing)管理框圖

　　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(tu)2，靜態電(dian)源路徑管(guan)理(li)的瞬態電(dian)流響應

　　靜態電源路徑管路

　　靜態電源路徑管理(SPPM)是一個(ge)簡化(hua)的解(jie)決辦法(fa)，能達到上面(mian)提到的第一個(ge)目標，不會(hui)出現(xian)電(dian)壓下降的情況。然而，它(ta)沒法(fa)解(jie)決第二(er)個(ge)問題，即區分系統(tong)和充電(dian)電(dian)流的優(you)先級。

　　SPPM機制的(de)(de)概念如(ru)圖(tu)3所示。主FET QMAIN是充電(dian)控制器元件(jian)。開(kai)(kai)關(guan)SW1連接電(dian)池(chi)和(he)系統。當(dang)電(dian)池(chi)電(dian)壓(ya)(ya)高于VPPM閾值(系統的(de)(de)最小工作電(dian)壓(ya)(ya)，一般是3.2V)，開(kai)(kai)關(guan)導通，無論外(wai)部電(dian)源存在與(yu)否，電(dian)池(chi)都會連到系統。這樣(yang)，當(dang)系統突然汲取電(dian)流(liu)(liu)時，由于開(kai)(kai)關(guan)已經處在導通狀(zhuang)態，電(dian)池(chi)能夠隨(sui)時提供系統所需的(de)(de)電(dian)流(liu)(liu)。這樣(yang)就解決(jue)了(le)電(dian)壓(ya)(ya)降和(he)電(dian)流(liu)(liu)畸變問(wen)題，如(ru)圖(tu)5所示。由于在設計中(zhong)僅(jin)需要一個調(diao)整元件(jian)對電(dian)池(chi)的(de)(de)充電(dian)電(dian)壓(ya)(ya)或電(dian)流(liu)(liu)進(jin)行調(diao)節，IC設計成本(ben)和(he)復(fu)雜度也降低(di)(di)了(le)。如(ru)果(guo)需要極低(di)(di)阻抗的(de)(de)開(kai)(kai)關(guan)，圖(tu)3中(zhong)的(de)(de)開(kai)(kai)關(guan)SW1可以放到IC外(wai)面來實現，進(jin)一步(bu)降低(di)(di)成本(ben)。

　　如果電池(chi)電壓(ya)(ya)低于VPPM的(de)閾值，SW1就開啟(qi)(qi)，VOUT將變成4.2V的(de)恒壓(ya)(ya)源，向(xiang)系(xi)(xi)統(tong)供電。與此同時，50mA的(de)恒流(liu)源ITRKL被激活，在涓流(liu)模式下對(dui)電池(chi)充電，直到(dao)電壓(ya)(ya)達到(dao)VPPM閾值(有一(yi)定(ding)滯后)，然后SW1會關閉，電池(chi)就連到(dao)系(xi)(xi)統(tong)上。這(zhe)樣就解(jie)決了沒電電池(chi)的(de)啟(qi)(qi)動問(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(li)框圖

　　圖4，靜態電源路徑管理控制(zhi)流程

　　圖5，靜(jing)態(tai)電(dian)源路徑管理的瞬態(tai)電(dian)流(liu)響應