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，但對電池充電器芯片(pian)還沒有達成(cheng)一(yi)個(ge)同樣統一(yi)的(de)(de)意見。作為控(kong)制鋰離子(zi)充(chong)電(dian)狀態(tai)的(de)(de)功率器件，電(dian)池(chi)充(chong)電(dian)器芯片(pian)在便攜式(shi)系統設計中扮演著(zhu)(zhu)重要的(de)(de)角(jiao)色(se)。然而，設計師(shi)們(men)還在使用著(zhu)(zhu)從較老并且相對粗糙(cao)和低成(cheng)本的(de)(de)充(chong)電(dian)器件、到(dao)較新的(de)(de)更復(fu)(fu)雜芯片(pian)等各種各樣的(de)(de)器件，而后者集成(cheng)了越來越復(fu)(fu)雜的(de)(de)智能，可以(yi)延長電(dian)池(chi)壽命，保護被(bei)充(chong)電(dian)系統不(bu)受損害(hai)。

　　安全第一

　　便攜式系(xi)統設計師面(mian)臨的(de)挑戰是：如何快速高效地(di)對系(xi)統進行充(chong)(chong)電(dian)(dian)，同時不影(ying)響(xiang)用(yong)戶安(an)全或損壞電(dian)(dian)池(chi)，并且要占用(yong)最(zui)少的(de)電(dian)(dian)路板面(mian)積(ji)。鋰(li)離子充(chong)(chong)電(dian)(dian)器通常采用(yong)三種(zhong)充(chong)(chong)電(dian)(dian)模式來最(zui)大化充(chong)(chong)電(dian)(dian)效率并確(que)保用(yong)戶安(an)全性。深度放電(dian)(dian)的(de)電(dian)(dian)池(chi)必須先用(yong)較小的(de)電(dian)(dian)流進行逐步預充(chong)(chong)電(dian)(dian)，將電(dian)(dian)池(chi)電(dian)(dian)壓慢慢提升到(dao)安(an)全閥值之上(shang)。

　　就拿(na)工作電(dian)(dian)壓(ya)范圍(wei)是(shi)2.8V到4.2V的(de)單節鋰離子電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)器來說(shuo)，它通常(chang)會測量被充(chong)(chong)電(dian)(dian)池(chi)的(de)電(dian)(dian)壓(ya)，當電(dian)(dian)池(chi)電(dian)(dian)壓(ya)低(di)于3V時，它將進入(ru)預充(chong)(chong)或“慢充(chong)(chong)”模(mo)式(shi)。慢充(chong)(chong)模(mo)式(shi)可(ke)以在電(dian)(dian)池(chi)內阻很(hen)低(di)時防(fang)止(zhi)對電(dian)(dian)池(chi)高(gao)速(su)充(chong)(chong)電(dian)(dian)，從而盡量減(jian)少(shao)發熱。一般預充(chong)(chong)期(qi)間的(de)充(chong)(chong)電(dian)(dian)速(su)率約是(shi)全速(su)充(chong)(chong)電(dian)(dian)時的(de)10%。

　　一旦電池達到最小電壓值，充電器就切換到(dao)恒流或快充(chong)(chong)(chong)模式(shi)，此時(shi)(shi)將對(dui)電(dian)(dian)池全速充(chong)(chong)(chong)電(dian)(dian)，直到(dao)電(dian)(dian)池達到(dao)接近(jin)滿充(chong)(chong)(chong)電(dian)(dian)壓的(de)第(di)二個閥值(zhi)。隨后充(chong)(chong)(chong)電(dian)(dian)器將進入(ru)恒壓模式(shi)，此時(shi)(shi)電(dian)(dian)池電(dian)(dian)壓保(bao)持不變，從而讓充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流逐(zhu)漸(jian)停止。當充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流小(xiao)于預設的(de)終止閥值(zhi)時(shi)(shi)，恒壓充(chong)(chong)(chong)電(dian)(dian)模式(shi)也就結束了。

　　熱(re)管理是電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)器設(she)計(ji)(ji)師面(mian)臨的(de)(de)(de)(de)(de)另一大挑戰。每個充(chong)電(dian)(dian)(dian)(dian)(dian)器芯片(pian)都(dou)會(hui)在充(chong)電(dian)(dian)(dian)(dian)(dian)過程中經(jing)歷由(you)于散熱(re)引起的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓下降。為了避免電(dian)(dian)(dian)(dian)(dian)池(chi)損壞或系統關斷(duan)，大多數(shu)充(chong)電(dian)(dian)(dian)(dian)(dian)器都(dou)集成了某種(zhong)形式的(de)(de)(de)(de)(de)控制機制來管理熱(re)量累積(ji)。較老的(de)(de)(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)器芯片(pian)常采用“非彼即此(ci)”的(de)(de)(de)(de)(de)方法來解(jie)決過熱(re)或過流(liu)問題――當熱(re)量達到預設(she)的(de)(de)(de)(de)(de)門限時它(ta)們(men)將簡單地中斷(duan)充(chong)電(dian)(dian)(dian)(dian)(dian)過程。較新的(de)(de)(de)(de)(de)器件則采用更復雜的(de)(de)(de)(de)(de)反饋技術連(lian)續監視裸(luo)片(pian)溫度，并(bing)以正比(bi)于環境(jing)溫度變(bian)化的(de)(de)(de)(de)(de)速(su)率(lv)動態(tai)或通過計(ji)(ji)算調整(zheng)充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)。這種(zhong)內置智能允許(xu)當前(qian)的(de)(de)(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)器芯片(pian)逐漸(jian)減少充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)，直到達到熱(re)平衡，裸(luo)片(pian)溫度停止上升。這種(zhong)技術能讓充(chong)電(dian)(dian)(dian)(dian)(dian)器以最大可能的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)對電(dian)(dian)(dian)(dian)(dian)池(chi)進行(xing)連(lian)續充(chong)電(dian)(dian)(dian)(dian)(dian)，同時不(bu)會(hui)導致系統關斷(duan)，從(cong)而縮短電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)時間。

　　MAX8804是(shi)美(mei)信集成產品公司去年7月份(fen)推出的(de)充(chong)(chong)電(dian)(dian)(dian)器芯片(pian)(pian)，它采用了專門的(de)熱(re)調整電(dian)(dian)(dian)路，可以在(zai)快速充(chong)(chong)電(dian)(dian)(dian)階段或系統處(chu)于高(gao)(gao)溫環境(jing)中(zhong)限制(zhi)裸片(pian)(pian)的(de)溫度。該充(chong)(chong)電(dian)(dian)(dian)器耐受(shou)30V的(de)直(zhi)流輸入(ru)電(dian)(dian)(dian)壓，只占用6平方(fang)毫米的(de)電(dian)(dian)(dian)路板面積。另外，像TI公司提(ti)供的(de)1A bq24060充(chong)(chong)電(dian)(dian)(dian)器可提(ti)供熱(re)過(guo)(guo)載保(bao)護功能，允許器件(jian)在(zai)環境(jing)溫度很(hen)高(gao)(gao)的(de)惡劣環境(jing)中(zhong)連(lian)(lian)續運行(xing)，例如夏天的(de)汽車或不小心(xin)連(lian)(lian)接到具有較高(gao)(gao)輸入(ru)電(dian)(dian)(dian)壓的(de)其它適(shi)配器。目(mu)前大(da)多數較新的(de)器件(jian)一般還會增加過(guo)(guo)壓保(bao)護機制(zhi)。

　　多種電壓源

　　有個越來越常見的(de)要求(qiu)是(shi)從(cong)不同電壓源(yuan)給電池充(chong)電，要點是(shi)在不使(shi)電壓源(yuan)過載(zai)的(de)情況下提供這(zhe)個功(gong)能。可以通過在輸入條件改變(bian)時動態調(diao)整(zheng)充(chong)電電流實(shi)現(xian)這(zhe)一(yi)功(gong)能。

　　舉例來(lai)說，移動用戶經常沒有時間(jian)去(qu)找交(jiao)(jiao)流電(dian)(dian)(dian)插座來(lai)給他們的(de)設(she)備(bei)(bei)充(chong)電(dian)(dian)(dian)，相(xiang)反，他們希望通(tong)過大多(duo)數電(dian)(dian)(dian)子設(she)備(bei)(bei)上都有的(de)眾多(duo)USB端(duan)口(kou)(kou)(kou)(kou)來(lai)給他們的(de)電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)，包(bao)括其它電(dian)(dian)(dian)池供電(dian)(dian)(dian)的(de)設(she)備(bei)(bei)，如筆記(ji)本電(dian)(dian)(dian)腦(nao)。因此，目前(qian)市場上的(de)許多(duo)充(chong)電(dian)(dian)(dian)器芯片支(zhi)持從交(jiao)(jiao)流和USB輸入口(kou)(kou)(kou)(kou)給單節鋰(li)電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)。此時的(de)挑(tiao)戰是補償(chang)USB端(duan)口(kou)(kou)(kou)(kou)提供的(de)不斷變化的(de)功(gong)率電(dian)(dian)(dian)平。隨著負(fu)載的(de)變化，系(xi)統必須控制恒定的(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流值以確保USB端(duan)口(kou)(kou)(kou)(kou)的(de)正(zheng)常操作。

　　一(yi)些(xie)充(chong)電(dian)(dian)(dian)器(qi)芯片(pian)(pian)利用簡(jian)單(dan)的(de)雙重方法(fa)支持USB操作(zuo)，該方法(fa)使用兩個預設的(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流值(通常是500mA和100mA)來支持USB端口(kou)允(yun)許的(de)最(zui)大電(dian)(dian)(dian)流或必要時(shi)的(de)最(zui)小電(dian)(dian)(dian)流以確保(bao)端口(kou)的(de)完整(zheng)性。通常這(zhe)要求接口(kou)邏(luo)輯嵌入(ru)在充(chong)電(dian)(dian)(dian)器(qi)芯片(pian)(pian)中，以便系統微控制器(qi)能(neng)夠連續讀取USB端口(kou)的(de)狀態，并(bing)指(zhi)示(shi)充(chong)電(dian)(dian)(dian)器(qi)從一(yi)個充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流切換到(dao)另一(yi)個充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流。

　　最近，有些充(chong)電器芯(xin)片制造商已經開發出能夠自動檢測USB端(duan)口(kou)的可(ke)用功率、并(bing)據此(ci)調整充(chong)電電流來(lai)最大化充(chong)電效率的芯(xin)片。另外，許多充(chong)電器芯(xin)片不需要(yao)用戶干涉，就能夠自動檢測電源|穩壓器|穩壓器類型并(bing)調整它(ta)們的充(chong)電過程。

　　當(dang)凌力爾(er)特公司的(de)LTC4075充(chong)電(dian)(dian)器芯片檢(jian)測(ce)到輸入端電(dian)(dian)源(yuan)(yuan)時，它(ta)能(neng)自動(dong)(dong)選擇(ze)合(he)適的(de)電(dian)(dian)源(yuan)(yuan)進行充(chong)電(dian)(dian)，同時不需要外接MOSFET、檢(jian)測(ce)電(dian)(dian)阻或阻流(liu)二(er)極管(guan)。Microchip Technology公司提供的(de)MCP73837也能(neng)提供類似自動(dong)(dong)的(de)電(dian)(dian)源(yuan)(yuan)選擇(ze)功能(neng)。

　　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(you)(you)代表性的(de)(de)例子是AT3663，這(zhe)是Advanced Analogic Technologies公司(AnalogicTech)提供的(de)(de)1A線(xian)性電(dian)池充電(dian)器系(xi)列芯片(pian)的(de)(de)第一個產品，可(ke)以用來給最多兩節串聯的(de)(de)鋰(li)離子電(dian)池充電(dian)。AT3663采(cai)用該制造商的(de)(de)專有(you)(you)模(mo)塊化(hua)BCD工(gong)藝技(ji)術制造。這(zhe)種工(gong)藝集成了完全隔離的(de)(de)CMOS和高速互補雙極晶(jing)體管以及30V DMOS功(gong)率器件，沒(mei)有(you)(you)采(cai)用復雜(za)而且昂貴(gui)的(de)(de)外延(yan)附(fu)生或高溫擴散技(ji)術。

　　上(shang)述(shu)新(xin)工藝允許AAT3663支持從4V到(dao)13.2V的輸入電壓，因此(ci)設(she)計師可以(yi)自(zi)由(you)使用較(jiao)低成本的非穩壓適配器。