無論是做什么用(yong)途，或制造商是誰，手(shou)持式電(dian)子(zi)設備(bei)(bei)(bei)都有一(yi)(yi)個共同(tong)的(de)(de)(de)(de)特性(xing)：一(yi)(yi)個可(ke)充(chong)電(dian)的(de)(de)(de)(de)電(dian)池(chi)，多(duo)數情況下(xia)還有一(yi)(yi)個內(nei)建的(de)(de)(de)(de)充(chong)電(dian)電(dian)路(lu)(lu)。當(dang)(dang)一(yi)(yi)個AC適配器(qi)這樣的(de)(de)(de)(de)外(wai)部(bu)(bu)電(dian)源(yuan)或一(yi)(yi)個USB端口接(jie)到(dao)手(shou)持設備(bei)(bei)(bei)的(de)(de)(de)(de)輸入端，充(chong)電(dian)電(dian)路(lu)(lu)將對電(dian)池(chi)充(chong)電(dian)。當(dang)(dang)接(jie)到(dao)外(wai)部(bu)(bu)電(dian)源(yuan)時，如果設備(bei)(bei)(bei)正處在開機狀(zhuang)態，理(li)想(xiang)的(de)(de)(de)(de)情形是，設備(bei)(bei)(bei)應當(dang)(dang)從外(wai)部(bu)(bu)電(dian)源(yuan)汲取盡可(ke)能多(duo)的(de)(de)(de)(de)功率，以(yi)節(jie)省電(dian)池(chi)壽命。要實現這個功能則需要一(yi)(yi)個自動(dong)的(de)(de)(de)(de)電(dian)源(yuan)選擇(ze)電(dian)路(lu)(lu)，這個電(dian)路(lu)(lu)通常是集成在充(chong)電(dian)控制IC內(nei)。設計者(zhe)可(ke)以(yi)從動(dong)態或靜態電(dian)源(yuan)路(lu)(lu)徑管(guan)理(li)當(dang)(dang)中選擇(ze)其(qi)中的(de)(de)(de)(de)一(yi)(yi)種，進行電(dian)源(yuan)管(guan)理(li)。

　　在電(dian)(dian)池供電(dian)(dian)的(de)手持設備中(zhong)，動態(tai)電(dian)(dian)源路徑管理(DPPM)是更流(liu)行的(de)機制。DPPM功(gong)能框圖如圖1所示。主通(tong)(tong)路元(yuan)(yuan)件QMAIN是一個(ge)電(dian)(dian)壓(ya)穩(wen)壓(ya)器(qi)，提(ti)供一個(ge)經過穩(wen)壓(ya)的(de)輸出(chu)電(dian)(dian)壓(ya)VOUT。第二個(ge)通(tong)(tong)路元(yuan)(yuan)件QCharge是充電(dian)(dian)控制元(yuan)(yuan)件，由VOUT供電(dian)(dian)，提(ti)供恒定的(de)電(dian)(dian)流(liu)或恒定的(de)電(dian)(dian)壓(ya)對電(dian)(dian)池充電(dian)(dian)。在充電(dian)(dian)期間，如果輸出(chu)電(dian)(dian)流(liu)超過電(dian)(dian)源的(de)電(dian)(dian)流(liu)限值，QCharge就會變成一個(ge)開關，將電(dian)(dian)池連到系統上，提(ti)供一部分所需的(de)輸出(chu)電(dian)(dian)流(liu)。

　　DPPM有(you)幾(ji)個(ge)(ge)(ge)好處。首先(xian)，當電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)完(wan)全(quan)(quan)放電(dian)(dian)(dian)(dian)(dian)時(shi)(shi)(shi)(電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)耗(hao)(hao)盡的(de)(de)情(qing)況)，DPPM能讓(rang)外部(bu)電(dian)(dian)(dian)(dian)(dian)源立刻給(gei)設(she)備(bei)供電(dian)(dian)(dian)(dian)(dian)。如(ru)果(guo)沒有(you)電(dian)(dian)(dian)(dian)(dian)源路(lu)徑(jing)管理(li)，在電(dian)(dian)(dian)(dian)(dian)量(liang)耗(hao)(hao)盡的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)被充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)到(dao)(dao)(dao)系(xi)統能夠(gou)啟(qi)動的(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)等(deng)級(ji)之前(一(yi)般是(shi)(shi)高于3V)，系(xi)統是(shi)(shi)無法上電(dian)(dian)(dian)(dian)(dian)的(de)(de)。這個(ge)(ge)(ge)等(deng)待周期取決于充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)路(lu)的(de)(de)涓流充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)設(she)定，可能是(shi)(shi)幾(ji)分(fen)(fen)鐘(zhong)到(dao)(dao)(dao)十分(fen)(fen)鐘(zhong)的(de)(de)時(shi)(shi)(shi)間(jian)。其次，當用(yong)外部(bu)電(dian)(dian)(dian)(dian)(dian)源對電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)(shi)(shi)，DPPM會把(ba)來自外部(bu)電(dian)(dian)(dian)(dian)(dian)源的(de)(de)電(dian)(dian)(dian)(dian)(dian)流分(fen)(fen)到(dao)(dao)(dao)兩個(ge)(ge)(ge)路(lu)徑(jing)中(zhong)，一(yi)條(tiao)路(lu)徑(jing)為(wei)手持設(she)備(bei)提供必要的(de)(de)功率，另一(yi)條(tiao)路(lu)徑(jing)輸(shu)出充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流，來給(gei)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)。當外部(bu)電(dian)(dian)(dian)(dian)(dian)源的(de)(de)輸(shu)入電(dian)(dian)(dian)(dian)(dian)流達到(dao)(dao)(dao)限值時(shi)(shi)(shi)，電(dian)(dian)(dian)(dian)(dian)源路(lu)徑(jing)管理(li)會對輸(shu)入到(dao)(dao)(dao)手持系(xi)統的(de)(de)電(dian)(dian)(dian)(dian)(dian)流進行(xing)優先(xian)級(ji)分(fen)(fen)類。這樣如(ru)果(guo)當系(xi)統工作時(shi)(shi)(shi)，電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)正在充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)可以在最短的(de)(de)時(shi)(shi)(shi)間(jian)內(nei)充(chong)(chong)滿，因為(wei)動態(tai)控制的(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流是(shi)(shi)為(wei)這個(ge)(ge)(ge)目(mu)標而優化的(de)(de)。當外部(bu)電(dian)(dian)(dian)(dian)(dian)源被移(yi)走(zou)時(shi)(shi)(shi)，QCharge立刻完(wan)全(quan)(quan)打開，把(ba)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)連到(dao)(dao)(dao)系(xi)統上，向系(xi)統輸(shu)出所需的(de)(de)全(quan)(quan)部(bu)功率。

　　圖1，動(dong)態電源路徑管理(li)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2，靜態電(dian)源路徑管理的瞬態電(dian)流響應

　　靜態電源路徑管路

　　靜態電源路徑管理(SPPM)是(shi)一個(ge)簡化的解(jie)決辦法(fa)，能達到上面提到的第一個(ge)目標(biao)，不會出現電(dian)壓下降的情況。然而，它沒法(fa)解(jie)決第二(er)個(ge)問題(ti)，即(ji)區分系統和充電(dian)電(dian)流的優(you)先級。

　　SPPM機(ji)制(zhi)的(de)(de)概念如(ru)圖3所示。主FET QMAIN是(shi)充電(dian)(dian)(dian)(dian)(dian)(dian)控制(zhi)器元件。開(kai)(kai)(kai)關(guan)SW1連(lian)接電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)和系(xi)(xi)(xi)統(tong)。當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)高(gao)于VPPM閾值(系(xi)(xi)(xi)統(tong)的(de)(de)最小(xiao)工作電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，一(yi)般是(shi)3.2V)，開(kai)(kai)(kai)關(guan)導通，無(wu)論(lun)外(wai)部電(dian)(dian)(dian)(dian)(dian)(dian)源存在(zai)與否(fou)，電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)都會連(lian)到系(xi)(xi)(xi)統(tong)。這樣(yang)，當系(xi)(xi)(xi)統(tong)突然汲取電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)時(shi)，由于開(kai)(kai)(kai)關(guan)已經(jing)處在(zai)導通狀態(tai)，電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)能夠隨時(shi)提供系(xi)(xi)(xi)統(tong)所需的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。這樣(yang)就(jiu)解(jie)決了電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)降(jiang)和電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)畸變(bian)問(wen)題，如(ru)圖5所示。由于在(zai)設(she)計(ji)中僅需要一(yi)個調整元件對電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)或電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)進行調節，IC設(she)計(ji)成(cheng)本和復(fu)雜(za)度也降(jiang)低(di)了。如(ru)果需要極低(di)阻抗的(de)(de)開(kai)(kai)(kai)關(guan)，圖3中的(de)(de)開(kai)(kai)(kai)關(guan)SW1可以放到IC外(wai)面來(lai)實現，進一(yi)步降(jiang)低(di)成(cheng)本。

　　如果電池(chi)(chi)電壓低于VPPM的閾值(zhi)，SW1就(jiu)(jiu)開啟，VOUT將變成4.2V的恒壓源，向系統(tong)供電。與此同(tong)時，50mA的恒流源ITRKL被激活，在涓流模式下(xia)對電池(chi)(chi)充(chong)電，直到電壓達(da)到VPPM閾值(zhi)(有一定滯后)，然后SW1會(hui)關閉，電池(chi)(chi)就(jiu)(jiu)連到系統(tong)上。這樣就(jiu)(jiu)解決了沒電電池(chi)(chi)的啟動問(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(jing)態電源路徑(jing)管理框圖

　　圖4，靜態(tai)電(dian)源(yuan)路(lu)徑管理控制流程

　　圖5，靜(jing)態(tai)電源路徑管理的瞬態(tai)電流(liu)響應(ying)