無論是做什么(me)用途，或(huo)制造商是誰，手(shou)持式電(dian)(dian)子設備(bei)都有(you)一(yi)(yi)(yi)個(ge)共同的(de)特(te)性：一(yi)(yi)(yi)個(ge)可(ke)(ke)充(chong)(chong)電(dian)(dian)的(de)電(dian)(dian)池(chi)(chi)，多(duo)數情況下還有(you)一(yi)(yi)(yi)個(ge)內建的(de)充(chong)(chong)電(dian)(dian)電(dian)(dian)路(lu)(lu)。當(dang)(dang)一(yi)(yi)(yi)個(ge)AC適配(pei)器這(zhe)(zhe)樣的(de)外部(bu)(bu)電(dian)(dian)源(yuan)或(huo)一(yi)(yi)(yi)個(ge)USB端口接到(dao)手(shou)持設備(bei)的(de)輸入(ru)端，充(chong)(chong)電(dian)(dian)電(dian)(dian)路(lu)(lu)將(jiang)對電(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)。當(dang)(dang)接到(dao)外部(bu)(bu)電(dian)(dian)源(yuan)時，如果設備(bei)正(zheng)處在(zai)開(kai)機(ji)狀態，理(li)(li)想(xiang)的(de)情形是，設備(bei)應當(dang)(dang)從(cong)外部(bu)(bu)電(dian)(dian)源(yuan)汲取盡可(ke)(ke)能多(duo)的(de)功(gong)率(lv)，以節(jie)省電(dian)(dian)池(chi)(chi)壽命。要實現(xian)這(zhe)(zhe)個(ge)功(gong)能則需要一(yi)(yi)(yi)個(ge)自動的(de)電(dian)(dian)源(yuan)選擇電(dian)(dian)路(lu)(lu)，這(zhe)(zhe)個(ge)電(dian)(dian)路(lu)(lu)通常是集成在(zai)充(chong)(chong)電(dian)(dian)控制IC內。設計者可(ke)(ke)以從(cong)動態或(huo)靜(jing)態電(dian)(dian)源(yuan)路(lu)(lu)徑(jing)管理(li)(li)當(dang)(dang)中選擇其(qi)中的(de)一(yi)(yi)(yi)種，進行電(dian)(dian)源(yuan)管理(li)(li)。

　　在電(dian)(dian)池(chi)供(gong)(gong)電(dian)(dian)的(de)手持(chi)設備中(zhong)，動態電(dian)(dian)源(yuan)路(lu)(lu)徑管理(li)(DPPM)是(shi)(shi)更流行(xing)的(de)機制。DPPM功能框圖如圖1所(suo)示。主通路(lu)(lu)元(yuan)件QMAIN是(shi)(shi)一個(ge)(ge)電(dian)(dian)壓(ya)穩壓(ya)器，提(ti)供(gong)(gong)一個(ge)(ge)經(jing)過(guo)穩壓(ya)的(de)輸(shu)出電(dian)(dian)壓(ya)VOUT。第二個(ge)(ge)通路(lu)(lu)元(yuan)件QCharge是(shi)(shi)充(chong)電(dian)(dian)控制元(yuan)件，由VOUT供(gong)(gong)電(dian)(dian)，提(ti)供(gong)(gong)恒定(ding)的(de)電(dian)(dian)流或恒定(ding)的(de)電(dian)(dian)壓(ya)對電(dian)(dian)池(chi)充(chong)電(dian)(dian)。在充(chong)電(dian)(dian)期間，如果輸(shu)出電(dian)(dian)流超過(guo)電(dian)(dian)源(yuan)的(de)電(dian)(dian)流限值，QCharge就會變成(cheng)一個(ge)(ge)開關，將電(dian)(dian)池(chi)連到(dao)系統上(shang)，提(ti)供(gong)(gong)一部(bu)分所(suo)需的(de)輸(shu)出電(dian)(dian)流。

　　DPPM有幾(ji)個好(hao)處。首先，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)完(wan)全放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)(電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)耗盡的(de)(de)(de)(de)情況)，DPPM能讓(rang)外部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)立刻給設備(bei)供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。如果沒(mei)有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)路(lu)徑(jing)(jing)管(guan)理，在電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)量(liang)耗盡的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)被(bei)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)到(dao)(dao)系(xi)(xi)統(tong)(tong)能夠啟動的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)等級(ji)之前(qian)(一(yi)(yi)般是高于3V)，系(xi)(xi)統(tong)(tong)是無(wu)法上(shang)(shang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)。這(zhe)個等待周期取決(jue)于充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)的(de)(de)(de)(de)涓流充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)設定，可能是幾(ji)分鐘(zhong)到(dao)(dao)十分鐘(zhong)的(de)(de)(de)(de)時(shi)(shi)間(jian)。其次，當用外部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)對(dui)(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)，DPPM會把(ba)來自外部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流分到(dao)(dao)兩個路(lu)徑(jing)(jing)中(zhong)，一(yi)(yi)條(tiao)(tiao)路(lu)徑(jing)(jing)為(wei)手持設備(bei)提(ti)供必(bi)要的(de)(de)(de)(de)功率(lv)，另一(yi)(yi)條(tiao)(tiao)路(lu)徑(jing)(jing)輸出充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流，來給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。當外部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)(de)輸入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流達到(dao)(dao)限值時(shi)(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)路(lu)徑(jing)(jing)管(guan)理會對(dui)(dui)輸入到(dao)(dao)手持系(xi)(xi)統(tong)(tong)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流進行優(you)先級(ji)分類。這(zhe)樣如果當系(xi)(xi)統(tong)(tong)工作時(shi)(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)正在充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)可以(yi)在最短的(de)(de)(de)(de)時(shi)(shi)間(jian)內充(chong)(chong)(chong)(chong)(chong)滿，因為(wei)動態(tai)控制的(de)(de)(de)(de)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流是為(wei)這(zhe)個目標而優(you)化的(de)(de)(de)(de)。當外部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)被(bei)移(yi)走時(shi)(shi)，QCharge立刻完(wan)全打開，把(ba)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)連(lian)到(dao)(dao)系(xi)(xi)統(tong)(tong)上(shang)(shang)，向系(xi)(xi)統(tong)(tong)輸出所需的(de)(de)(de)(de)全部功率(lv)。

　　圖1，動態(tai)電源路徑管理框圖

　　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2，靜態電源路徑(jing)管理的瞬(shun)態電流響應

　　靜態電源路徑管路

　　靜態電源路徑管理(SPPM)是一(yi)(yi)個簡化的(de)(de)解決(jue)辦法，能達到上面提(ti)到的(de)(de)第一(yi)(yi)個目標(biao)，不會出現電(dian)壓(ya)下降的(de)(de)情況(kuang)。然(ran)而，它(ta)沒法解決(jue)第二個問題，即區分系(xi)統和充電(dian)電(dian)流的(de)(de)優先級。

　　SPPM機制的(de)概念如圖3所(suo)(suo)示。主(zhu)FET QMAIN是充(chong)電(dian)控制器(qi)元(yuan)件。開(kai)(kai)關(guan)(guan)SW1連(lian)(lian)接電(dian)池(chi)(chi)和(he)系(xi)(xi)統。當電(dian)池(chi)(chi)電(dian)壓(ya)高于VPPM閾值(系(xi)(xi)統的(de)最小工作電(dian)壓(ya)，一(yi)般是3.2V)，開(kai)(kai)關(guan)(guan)導通，無(wu)論外(wai)部電(dian)源(yuan)存在與否，電(dian)池(chi)(chi)都會連(lian)(lian)到(dao)(dao)系(xi)(xi)統。這樣，當系(xi)(xi)統突然(ran)汲取電(dian)流(liu)(liu)時，由(you)(you)于開(kai)(kai)關(guan)(guan)已經處(chu)在導通狀態，電(dian)池(chi)(chi)能夠隨時提供系(xi)(xi)統所(suo)(suo)需的(de)電(dian)流(liu)(liu)。這樣就解決了(le)電(dian)壓(ya)降和(he)電(dian)流(liu)(liu)畸變問題(ti)，如圖5所(suo)(suo)示。由(you)(you)于在設計中(zhong)僅需要(yao)一(yi)個調整(zheng)元(yuan)件對電(dian)池(chi)(chi)的(de)充(chong)電(dian)電(dian)壓(ya)或電(dian)流(liu)(liu)進(jin)行調節，IC設計成本(ben)和(he)復雜度(du)也降低了(le)。如果(guo)需要(yao)極(ji)低阻抗的(de)開(kai)(kai)關(guan)(guan)，圖3中(zhong)的(de)開(kai)(kai)關(guan)(guan)SW1可(ke)以放到(dao)(dao)IC外(wai)面(mian)來實現，進(jin)一(yi)步(bu)降低成本(ben)。

　　如果電(dian)(dian)池電(dian)(dian)壓低(di)于(yu)VPPM的閾值(zhi)，SW1就開啟(qi)，VOUT將(jiang)變成4.2V的恒壓源，向系統供(gong)電(dian)(dian)。與此同時，50mA的恒流(liu)源ITRKL被激(ji)活，在涓流(liu)模式下對(dui)電(dian)(dian)池充電(dian)(dian)，直到電(dian)(dian)壓達到VPPM閾值(zhi)(有一定(ding)滯后(hou))，然(ran)后(hou)SW1會關閉，電(dian)(dian)池就連(lian)到系統上。這樣(yang)就解決了沒電(dian)(dian)電(dian)(dian)池的啟(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(tu)3，靜態電源(yuan)路(lu)徑管理框圖(tu)

　　圖4，靜態電源路徑管理(li)控制流(liu)程

　　圖5，靜態電源路徑管理的瞬態電流(liu)響(xiang)應