電池壽命無疑是目前許多便攜式電子產品中最重要的特性。雖然許多便攜式電子行業已經廣泛采用鋰離子電池，因為這種電池具有容量大、尺寸小、重量輕和可靠耐用的特點，但對電池充電器芯(xin)(xin)片還(huan)(huan)沒(mei)有達成一個(ge)同樣(yang)統一的(de)(de)意見。作為控制(zhi)鋰離子(zi)充(chong)電(dian)狀(zhuang)態的(de)(de)功率器件，電(dian)池充(chong)電(dian)器芯(xin)(xin)片在便攜式系統設(she)(she)計中(zhong)扮演著重要的(de)(de)角色。然而(er)(er)，設(she)(she)計師們還(huan)(huan)在使用(yong)著從較(jiao)老并且相對(dui)粗糙和低成本的(de)(de)充(chong)電(dian)器件、到較(jiao)新(xin)的(de)(de)更復雜芯(xin)(xin)片等(deng)各種各樣(yang)的(de)(de)器件，而(er)(er)后者集成了越(yue)來越(yue)復雜的(de)(de)智能(neng)，可以延(yan)長電(dian)池壽(shou)命，保(bao)護被充(chong)電(dian)系統不受損(sun)害(hai)。

　　安全第一

　　便攜式系統設計(ji)師面(mian)臨的挑戰是：如何快速高效地對系統進行充電，同時不影響用戶(hu)安全(quan)或損壞電池，并且(qie)要占用最(zui)少(shao)的電路板面(mian)積。鋰離子充電器通常采用三種(zhong)充電模(mo)式來最(zui)大化充電效率并確(que)保用戶(hu)安全(quan)性。深度放電的電池必(bi)須先用較小(xiao)的電流進行逐步(bu)預充電，將電池電壓慢(man)慢(man)提升到安全(quan)閥值之上。

　　就(jiu)拿(na)工作電(dian)壓(ya)范(fan)圍是2.8V到4.2V的單節鋰(li)離子電(dian)池充(chong)(chong)電(dian)器來說，它通常(chang)會測量被充(chong)(chong)電(dian)池的電(dian)壓(ya)，當電(dian)池電(dian)壓(ya)低于3V時，它將進入預(yu)充(chong)(chong)或(huo)“慢(man)充(chong)(chong)”模式。慢(man)充(chong)(chong)模式可以(yi)在電(dian)池內阻很低時防(fang)止對(dui)電(dian)池高速(su)充(chong)(chong)電(dian)，從而盡量減少發熱。一般(ban)預(yu)充(chong)(chong)期間的充(chong)(chong)電(dian)速(su)率約(yue)是全速(su)充(chong)(chong)電(dian)時的10%。

　　一旦電池達到最小電壓值，充電器就(jiu)切換(huan)到恒(heng)流或(huo)快充(chong)(chong)模式，此時將對電(dian)(dian)(dian)池全速(su)充(chong)(chong)電(dian)(dian)(dian)，直(zhi)到電(dian)(dian)(dian)池達到接近滿充(chong)(chong)電(dian)(dian)(dian)壓的(de)(de)第二個閥值。隨(sui)后充(chong)(chong)電(dian)(dian)(dian)器將進(jin)入恒(heng)壓模式，此時電(dian)(dian)(dian)池電(dian)(dian)(dian)壓保(bao)持不變，從而讓充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流逐漸停止。當(dang)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流小于預設的(de)(de)終(zhong)止閥值時，恒(heng)壓充(chong)(chong)電(dian)(dian)(dian)模式也就(jiu)結束了。

　　熱(re)(re)管理(li)是(shi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)設計師面(mian)臨的(de)另一大挑戰(zhan)。每個充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)芯(xin)片(pian)(pian)(pian)都會在充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程中經歷由于散熱(re)(re)引(yin)起(qi)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓下(xia)降(jiang)。為了(le)避免電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)損壞或(huo)系統關斷，大多數充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)都集成了(le)某種(zhong)(zhong)形(xing)式(shi)的(de)控制機制來(lai)(lai)管理(li)熱(re)(re)量累積。較老(lao)的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)芯(xin)片(pian)(pian)(pian)常采用(yong)“非(fei)彼即此”的(de)方法來(lai)(lai)解決過(guo)熱(re)(re)或(huo)過(guo)流問題――當熱(re)(re)量達到預(yu)設的(de)門限時它們將簡單地(di)中斷充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程。較新的(de)器(qi)件則采用(yong)更復(fu)雜的(de)反饋技術連續監視裸(luo)片(pian)(pian)(pian)溫(wen)度(du)，并以(yi)正比于環(huan)境溫(wen)度(du)變化的(de)速率動態或(huo)通過(guo)計算調整(zheng)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流。這(zhe)種(zhong)(zhong)內置智能(neng)允許當前的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)芯(xin)片(pian)(pian)(pian)逐漸減少(shao)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流，直到達到熱(re)(re)平衡，裸(luo)片(pian)(pian)(pian)溫(wen)度(du)停止上升(sheng)。這(zhe)種(zhong)(zhong)技術能(neng)讓充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)以(yi)最大可能(neng)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)流對電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進(jin)行連續充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，同時不會導致系統關斷，從而縮短(duan)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時間。

　　MAX8804是美信集成產品公司(si)(si)去年7月份推出的充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)芯片，它采用(yong)了專門的熱(re)調整(zheng)電(dian)(dian)(dian)(dian)路，可以在快速充(chong)(chong)電(dian)(dian)(dian)(dian)階段(duan)或系統處于高(gao)溫環境(jing)中限制裸片的溫度(du)(du)。該充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)耐受30V的直流輸入電(dian)(dian)(dian)(dian)壓(ya)，只(zhi)占用(yong)6平方毫米(mi)的電(dian)(dian)(dian)(dian)路板面積(ji)。另外，像TI公司(si)(si)提(ti)供的1A bq24060充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)可提(ti)供熱(re)過(guo)載保護(hu)功(gong)能，允許器(qi)件在環境(jing)溫度(du)(du)很(hen)高(gao)的惡劣環境(jing)中連續運行，例如夏天的汽車(che)或不(bu)小心(xin)連接到具有較(jiao)高(gao)輸入電(dian)(dian)(dian)(dian)壓(ya)的其它適配器(qi)。目前大多數(shu)較(jiao)新的器(qi)件一(yi)般還會增(zeng)加過(guo)壓(ya)保護(hu)機制。

　　多種電壓源

　　有個(ge)(ge)越來越常見的要(yao)求是(shi)從不同(tong)電壓源給(gei)電池充電，要(yao)點是(shi)在不使(shi)電壓源過載的情(qing)況下(xia)提供(gong)這(zhe)個(ge)(ge)功能(neng)。可(ke)以通過在輸入條件改變(bian)時動態調整充電電流實現這(zhe)一(yi)功能(neng)。

　　舉(ju)例(li)來(lai)(lai)說(shuo)，移動用戶經常(chang)沒有時間去找交流電(dian)(dian)(dian)(dian)插座來(lai)(lai)給他(ta)們(men)的(de)設備充(chong)(chong)電(dian)(dian)(dian)(dian)，相(xiang)反，他(ta)們(men)希望通過大多數電(dian)(dian)(dian)(dian)子設備上都有的(de)眾(zhong)多USB端口來(lai)(lai)給他(ta)們(men)的(de)電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)，包括其它(ta)電(dian)(dian)(dian)(dian)池(chi)供電(dian)(dian)(dian)(dian)的(de)設備，如(ru)筆(bi)記(ji)本(ben)電(dian)(dian)(dian)(dian)腦。因(yin)此，目前市(shi)場上的(de)許多充(chong)(chong)電(dian)(dian)(dian)(dian)器芯片支持從交流和USB輸入口給單(dan)節鋰電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)。此時的(de)挑戰是補償USB端口提(ti)供的(de)不斷變(bian)化的(de)功率電(dian)(dian)(dian)(dian)平。隨著(zhu)負載(zai)的(de)變(bian)化，系統必須控制恒定的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流值以確保USB端口的(de)正(zheng)常(chang)操(cao)作。

　　一些充電(dian)(dian)器(qi)芯片利用(yong)簡單的(de)雙(shuang)重方(fang)法支持USB操作，該方(fang)法使(shi)用(yong)兩個(ge)(ge)預設的(de)充電(dian)(dian)電(dian)(dian)流(liu)值(zhi)(通(tong)常(chang)是500mA和100mA)來(lai)支持USB端(duan)口(kou)允許的(de)最(zui)大(da)電(dian)(dian)流(liu)或必要時(shi)的(de)最(zui)小電(dian)(dian)流(liu)以(yi)確保端(duan)口(kou)的(de)完整性。通(tong)常(chang)這要求接口(kou)邏輯嵌入(ru)在充電(dian)(dian)器(qi)芯片中(zhong)，以(yi)便系統微控制器(qi)能夠(gou)連續讀取USB端(duan)口(kou)的(de)狀態，并指示充電(dian)(dian)器(qi)從一個(ge)(ge)充電(dian)(dian)電(dian)(dian)流(liu)切換到另一個(ge)(ge)充電(dian)(dian)電(dian)(dian)流(liu)。

　　最近，有(you)些充電(dian)器芯片制(zhi)造商已經(jing)開(kai)發出能夠自動檢(jian)測USB端口的可用功率、并據此調整充電(dian)電(dian)流(liu)來最大化充電(dian)效率的芯片。另外，許(xu)多充電(dian)器芯片不需要用戶(hu)干涉，就能夠自動檢(jian)測電(dian)源|穩壓(ya)器|穩壓(ya)器類型并調整它們的充電(dian)過程(cheng)。

　　當凌力爾特公司的LTC4075充電(dian)(dian)器芯(xin)片檢測到輸(shu)入端電(dian)(dian)源時，它能自動選擇合適的電(dian)(dian)源進行充電(dian)(dian)，同時不(bu)需要外接MOSFET、檢測電(dian)(dian)阻(zu)或阻(zu)流二極(ji)管(guan)。Microchip Technology公司提供的MCP73837也能提供類似自動的電(dian)(dian)源選擇功能。

　　采用雙節電池

　　隨著便攜式系統設計復雜性的提高，它們使用的子系統、顯示器和處理器的數量與類型也越來越多，單節鋰離子電池已經無法滿足系統需要。因此，一些便攜式媒體播放器、高性能SLR型數碼相機和GPS導航系統都開始采用串聯的兩節鋰離子電池供電。這些便攜式產品一般要求輸入在8.4V和8.8V之間進行充電。設計師以前都是使用分立器件實現這種設計，但支持這個要求的新一代充電器芯片已經開始上市。

　　具有代表性(xing)的例子是AT3663，這(zhe)是Advanced Analogic Technologies公司(AnalogicTech)提供的1A線(xian)性(xing)電(dian)池充(chong)電(dian)器系(xi)列芯片的第一個產品，可以(yi)用(yong)來給最多兩(liang)節(jie)串聯的鋰離(li)子電(dian)池充(chong)電(dian)。AT3663采(cai)用(yong)該制造商的專有模塊化(hua)BCD工(gong)藝技術(shu)制造。這(zhe)種工(gong)藝集(ji)成(cheng)了(le)完全隔離(li)的CMOS和高速互補雙(shuang)極晶體管以(yi)及(ji)30V DMOS功率器件，沒有采(cai)用(yong)復(fu)雜而且昂貴的外延附生或高溫擴散技術(shu)。

　　上述新工藝允許AAT3663支持從4V到13.2V的(de)輸入電(dian)壓，因此設計師可(ke)以自由使用較低成本的(de)非穩壓適配器。