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還(huan)沒(mei)有達成一個同樣統一的(de)意(yi)見(jian)。作(zuo)為控制鋰(li)離子充(chong)電(dian)狀態的(de)功(gong)率器件(jian)，電(dian)池(chi)充(chong)電(dian)器芯片在(zai)便攜式系統設計中扮演著重(zhong)要的(de)角色。然(ran)而(er)，設計師(shi)們還(huan)在(zai)使(shi)用著從較老并且相對(dui)粗(cu)糙和低成本的(de)充(chong)電(dian)器件(jian)、到較新的(de)更(geng)復雜芯片等(deng)各種(zhong)各樣的(de)器件(jian)，而(er)后者(zhe)集成了越來越復雜的(de)智能(neng)，可(ke)以延長電(dian)池(chi)壽命，保護被充(chong)電(dian)系統不受(shou)損害。

　　安全第一

　　便攜式系統設計師面臨的挑(tiao)戰(zhan)是：如(ru)何快速高效地對(dui)系統進(jin)行(xing)充(chong)電(dian)(dian)(dian)(dian)，同時不影響用戶安(an)全(quan)或(huo)損壞電(dian)(dian)(dian)(dian)池，并且要占用最少的電(dian)(dian)(dian)(dian)路板面積。鋰離(li)子充(chong)電(dian)(dian)(dian)(dian)器通(tong)常采用三種充(chong)電(dian)(dian)(dian)(dian)模式來最大化(hua)充(chong)電(dian)(dian)(dian)(dian)效率并確(que)保用戶安(an)全(quan)性(xing)。深(shen)度放電(dian)(dian)(dian)(dian)的電(dian)(dian)(dian)(dian)池必(bi)須先用較小的電(dian)(dian)(dian)(dian)流進(jin)行(xing)逐步(bu)預充(chong)電(dian)(dian)(dian)(dian)，將電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓慢(man)慢(man)提升到安(an)全(quan)閥值之上。

　　就拿(na)工作電(dian)(dian)(dian)(dian)壓(ya)(ya)范圍是(shi)2.8V到4.2V的(de)單節鋰離(li)子電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)器來說，它通常會測量(liang)被充(chong)電(dian)(dian)(dian)(dian)池的(de)電(dian)(dian)(dian)(dian)壓(ya)(ya)，當電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)(ya)低于3V時，它將(jiang)進(jin)入(ru)預充(chong)或“慢(man)充(chong)”模式(shi)。慢(man)充(chong)模式(shi)可以在電(dian)(dian)(dian)(dian)池內阻很低時防(fang)止對電(dian)(dian)(dian)(dian)池高速充(chong)電(dian)(dian)(dian)(dian)，從而盡量(liang)減少發熱(re)。一般(ban)預充(chong)期間的(de)充(chong)電(dian)(dian)(dian)(dian)速率約是(shi)全速充(chong)電(dian)(dian)(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(heng)(heng)流(liu)或快充(chong)模(mo)式(shi)，此(ci)時(shi)將對電(dian)池全速(su)充(chong)電(dian)，直到(dao)電(dian)池達到(dao)接近滿充(chong)電(dian)壓的第二個閥(fa)值(zhi)。隨后充(chong)電(dian)器將進入恒(heng)(heng)壓模(mo)式(shi)，此(ci)時(shi)電(dian)池電(dian)壓保持(chi)不(bu)變，從(cong)而讓充(chong)電(dian)電(dian)流(liu)逐漸停止。當充(chong)電(dian)電(dian)流(liu)小(xiao)于預設的終止閥(fa)值(zhi)時(shi)，恒(heng)(heng)壓充(chong)電(dian)模(mo)式(shi)也就結束(shu)了。

　　熱管(guan)理(li)是電(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)器(qi)設計師(shi)面臨(lin)的(de)(de)另一大挑戰(zhan)。每個充(chong)(chong)(chong)電(dian)(dian)器(qi)芯片(pian)都會在(zai)充(chong)(chong)(chong)電(dian)(dian)過(guo)(guo)程中經歷(li)由(you)于散熱引起(qi)的(de)(de)電(dian)(dian)壓下降。為了避(bi)免電(dian)(dian)池(chi)(chi)損壞或系統(tong)關斷(duan)(duan)，大多數充(chong)(chong)(chong)電(dian)(dian)器(qi)都集成了某種形(xing)式的(de)(de)控制機制來管(guan)理(li)熱量(liang)(liang)累積。較老的(de)(de)充(chong)(chong)(chong)電(dian)(dian)器(qi)芯片(pian)常(chang)采(cai)(cai)用“非(fei)彼即此”的(de)(de)方法來解決過(guo)(guo)熱或過(guo)(guo)流(liu)問題――當(dang)熱量(liang)(liang)達到預設的(de)(de)門限時它(ta)們(men)將簡(jian)單地中斷(duan)(duan)充(chong)(chong)(chong)電(dian)(dian)過(guo)(guo)程。較新的(de)(de)器(qi)件則采(cai)(cai)用更復雜的(de)(de)反饋(kui)技術連(lian)續監視裸片(pian)溫(wen)(wen)度(du)(du)，并以(yi)正比于環境溫(wen)(wen)度(du)(du)變化的(de)(de)速率動態或通過(guo)(guo)計算調整充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)。這種內(nei)置智能允許當(dang)前的(de)(de)充(chong)(chong)(chong)電(dian)(dian)器(qi)芯片(pian)逐(zhu)漸減少充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)，直到達到熱平衡，裸片(pian)溫(wen)(wen)度(du)(du)停止上升。這種技術能讓充(chong)(chong)(chong)電(dian)(dian)器(qi)以(yi)最大可能的(de)(de)電(dian)(dian)流(liu)對電(dian)(dian)池(chi)(chi)進行連(lian)續充(chong)(chong)(chong)電(dian)(dian)，同時不會導致系統(tong)關斷(duan)(duan)，從而縮短(duan)電(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)時間。

　　MAX8804是(shi)美信(xin)集成(cheng)產品(pin)公司去年7月份推出(chu)的(de)(de)充(chong)電(dian)(dian)器芯片，它采用(yong)了專(zhuan)門的(de)(de)熱調(diao)整(zheng)電(dian)(dian)路(lu)，可以在快速充(chong)電(dian)(dian)階段(duan)或系統處于高溫(wen)(wen)環境(jing)中(zhong)限制(zhi)裸片的(de)(de)溫(wen)(wen)度(du)(du)。該充(chong)電(dian)(dian)器耐受30V的(de)(de)直流(liu)輸入電(dian)(dian)壓，只占用(yong)6平方毫米的(de)(de)電(dian)(dian)路(lu)板面積。另外，像TI公司提供的(de)(de)1A bq24060充(chong)電(dian)(dian)器可提供熱過載(zai)保護功(gong)能，允許(xu)器件在環境(jing)溫(wen)(wen)度(du)(du)很高的(de)(de)惡(e)劣環境(jing)中(zhong)連續運行，例如夏天(tian)的(de)(de)汽車或不小心連接到(dao)具有較(jiao)(jiao)高輸入電(dian)(dian)壓的(de)(de)其它適配器。目前(qian)大多(duo)數較(jiao)(jiao)新(xin)的(de)(de)器件一般還會增加過壓保護機制(zhi)。

　　多種電壓源

　　有(you)個(ge)(ge)越來越常(chang)見的要求是從不同電壓源給電池(chi)充(chong)電，要點是在不使(shi)電壓源過(guo)載(zai)的情(qing)況下提供這個(ge)(ge)功能。可(ke)以通過(guo)在輸入條(tiao)件改變時動態調(diao)整充(chong)電電流實現這一(yi)功能。

　　舉例(li)來說，移(yi)動用戶經常沒有(you)時(shi)間去找交(jiao)流(liu)電(dian)(dian)插座來給(gei)他們(men)的設備(bei)充(chong)(chong)(chong)(chong)電(dian)(dian)，相反，他們(men)希(xi)望(wang)通過(guo)大多(duo)(duo)數電(dian)(dian)子設備(bei)上都(dou)有(you)的眾(zhong)多(duo)(duo)USB端(duan)口(kou)來給(gei)他們(men)的電(dian)(dian)池充(chong)(chong)(chong)(chong)電(dian)(dian)，包括其它電(dian)(dian)池供(gong)電(dian)(dian)的設備(bei)，如筆(bi)記本電(dian)(dian)腦。因(yin)此，目前(qian)市場上的許多(duo)(duo)充(chong)(chong)(chong)(chong)電(dian)(dian)器芯片支持(chi)從交(jiao)流(liu)和USB輸(shu)入(ru)口(kou)給(gei)單節鋰電(dian)(dian)池充(chong)(chong)(chong)(chong)電(dian)(dian)。此時(shi)的挑戰是補償USB端(duan)口(kou)提(ti)供(gong)的不(bu)斷變(bian)化(hua)(hua)的功率電(dian)(dian)平(ping)。隨著負載的變(bian)化(hua)(hua)，系(xi)統必須控(kong)制恒(heng)定的充(chong)(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)值以確保(bao)USB端(duan)口(kou)的正常操作。

　　一些充(chong)(chong)(chong)電(dian)(dian)器芯片利(li)用簡單的(de)雙重(zhong)方法支(zhi)持USB操作，該方法使用兩個(ge)預設(she)的(de)充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)值(zhi)(通(tong)常是(shi)500mA和100mA)來支(zhi)持USB端口(kou)允許(xu)的(de)最(zui)大電(dian)(dian)流(liu)(liu)或必要時的(de)最(zui)小(xiao)電(dian)(dian)流(liu)(liu)以確保(bao)端口(kou)的(de)完整性(xing)。通(tong)常這要求接口(kou)邏輯(ji)嵌(qian)入在充(chong)(chong)(chong)電(dian)(dian)器芯片中，以便(bian)系(xi)統微控(kong)制器能(neng)夠連續(xu)讀取USB端口(kou)的(de)狀態，并(bing)指示(shi)充(chong)(chong)(chong)電(dian)(dian)器從(cong)一個(ge)充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)切換到另一個(ge)充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)。

　　最近，有些(xie)充電(dian)(dian)器(qi)(qi)芯(xin)(xin)片制(zhi)造商已經開(kai)發出能夠自動(dong)檢(jian)測(ce)USB端口的(de)(de)可用(yong)(yong)功(gong)率(lv)、并據此(ci)調整充電(dian)(dian)電(dian)(dian)流來(lai)最大化充電(dian)(dian)效率(lv)的(de)(de)芯(xin)(xin)片。另外，許(xu)多(duo)充電(dian)(dian)器(qi)(qi)芯(xin)(xin)片不需要(yao)用(yong)(yong)戶干涉，就能夠自動(dong)檢(jian)測(ce)電(dian)(dian)源(yuan)|穩壓器(qi)(qi)|穩壓器(qi)(qi)類型并調整它們(men)的(de)(de)充電(dian)(dian)過程。

　　當(dang)凌力爾特(te)公司的(de)LTC4075充(chong)電(dian)器芯(xin)片檢(jian)測到輸入端電(dian)源(yuan)時，它能自動(dong)選擇合適的(de)電(dian)源(yuan)進行充(chong)電(dian)，同時不需要外接MOSFET、檢(jian)測電(dian)阻(zu)或阻(zu)流二極管。Microchip Technology公司提供(gong)(gong)的(de)MCP73837也(ye)能提供(gong)(gong)類似自動(dong)的(de)電(dian)源(yuan)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(you)代表性(xing)的(de)例子是(shi)AT3663，這(zhe)是(shi)Advanced Analogic Technologies公司(AnalogicTech)提供的(de)1A線性(xing)電池充(chong)電器系列芯片(pian)的(de)第(di)一個產品，可(ke)以用來(lai)給最多兩(liang)節串聯的(de)鋰(li)離子電池充(chong)電。AT3663采用該(gai)制造(zao)商的(de)專有(you)模塊化BCD工藝(yi)技(ji)術制造(zao)。這(zhe)種工藝(yi)集成了完全隔離的(de)CMOS和高(gao)速(su)互(hu)補雙(shuang)極(ji)晶(jing)體(ti)管以及(ji)30V DMOS功率器件，沒(mei)有(you)采用復雜而且(qie)昂貴的(de)外延附生(sheng)或高(gao)溫擴散技(ji)術。

　　上述(shu)新工藝允許AAT3663支持從4V到(dao)13.2V的輸入(ru)電壓(ya)，因(yin)此設計(ji)師可以(yi)自由使用(yong)較低成(cheng)本的非穩壓(ya)適配器。