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)片(pian)還沒(mei)有達成一(yi)個(ge)同樣統一(yi)的意見。作(zuo)為控制鋰(li)離子充(chong)電(dian)狀(zhuang)態的功率器(qi)件，電(dian)池(chi)充(chong)電(dian)器(qi)芯(xin)片(pian)在便攜式系統設計中(zhong)扮演著重要的角色(se)。然(ran)而，設計師們(men)還在使用著從較老并且相(xiang)對(dui)粗糙和低成本的充(chong)電(dian)器(qi)件、到較新的更復雜芯(xin)片(pian)等(deng)各種各樣的器(qi)件，而后(hou)者集(ji)成了越來越復雜的智(zhi)能(neng)，可以延長電(dian)池(chi)壽(shou)命，保護(hu)被充(chong)電(dian)系統不受損害。

　　安全第一

　　便攜式(shi)系統設計師(shi)面(mian)臨的(de)挑戰是：如何快速高效地對系統進行充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，同時不影(ying)響用(yong)戶安(an)全(quan)或(huo)損(sun)壞電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)，并且要(yao)占(zhan)用(yong)最少(shao)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)路板(ban)面(mian)積。鋰離子充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器通(tong)常采用(yong)三種充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)模式(shi)來最大化充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)效率并確(que)保用(yong)戶安(an)全(quan)性。深度(du)放電(dian)(dian)(dian)(dian)(dian)(dian)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)必須(xu)先用(yong)較(jiao)小的(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)進行逐步預充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，將(jiang)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓慢慢提升到安(an)全(quan)閥值之上。

　　就拿工作電(dian)(dian)壓范圍是2.8V到(dao)4.2V的(de)單節鋰(li)離子電(dian)(dian)池(chi)充(chong)電(dian)(dian)器來(lai)說，它通(tong)常會測量(liang)被充(chong)電(dian)(dian)池(chi)的(de)電(dian)(dian)壓，當電(dian)(dian)池(chi)電(dian)(dian)壓低于3V時(shi)(shi)，它將(jiang)進入預(yu)充(chong)或“慢(man)充(chong)”模式。慢(man)充(chong)模式可(ke)以在電(dian)(dian)池(chi)內阻很低時(shi)(shi)防止對電(dian)(dian)池(chi)高速(su)充(chong)電(dian)(dian)，從而(er)盡量(liang)減少(shao)發熱。一般預(yu)充(chong)期間的(de)充(chong)電(dian)(dian)速(su)率約是全速(su)充(chong)電(dian)(dian)時(shi)(shi)的(de)10%。

　　一旦電池達到最小電壓值，充電器就切(qie)換到(dao)恒流或快(kuai)充模式(shi)，此時(shi)將(jiang)(jiang)對電(dian)(dian)(dian)(dian)(dian)池全(quan)速充電(dian)(dian)(dian)(dian)(dian)，直到(dao)電(dian)(dian)(dian)(dian)(dian)池達到(dao)接近滿充電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)的第二個閥值(zhi)。隨后充電(dian)(dian)(dian)(dian)(dian)器將(jiang)(jiang)進入恒壓(ya)(ya)模式(shi)，此時(shi)電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)保(bao)持不(bu)變，從而讓充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流逐漸停止。當(dang)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流小于預(yu)設的終止閥值(zhi)時(shi)，恒壓(ya)(ya)充電(dian)(dian)(dian)(dian)(dian)模式(shi)也就結束(shu)了。

　　熱(re)管理是電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)設(she)計師面臨(lin)的(de)(de)另一大挑(tiao)戰。每個充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)芯(xin)(xin)片(pian)(pian)都會在(zai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)過程(cheng)中經歷由于散熱(re)引起(qi)的(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)下降。為了(le)避免電(dian)(dian)(dian)(dian)(dian)池(chi)損(sun)壞或(huo)系統(tong)關斷，大多數充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)都集成了(le)某(mou)種形式的(de)(de)控制機制來管理熱(re)量(liang)累積。較老(lao)的(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)芯(xin)(xin)片(pian)(pian)常采用“非彼即此(ci)”的(de)(de)方法來解決過熱(re)或(huo)過流(liu)問題――當熱(re)量(liang)達到預設(she)的(de)(de)門限時(shi)它們將簡單地(di)中斷充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)過程(cheng)。較新的(de)(de)器(qi)件則采用更復雜的(de)(de)反(fan)饋技術(shu)連續(xu)監視裸片(pian)(pian)溫度，并以(yi)正(zheng)比(bi)于環境溫度變化的(de)(de)速率動態或(huo)通過計算調(diao)整充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)。這種內置智能允(yun)許當前的(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)芯(xin)(xin)片(pian)(pian)逐漸減少充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)，直到達到熱(re)平衡(heng)，裸片(pian)(pian)溫度停(ting)止上升。這種技術(shu)能讓充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)以(yi)最大可能的(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)對電(dian)(dian)(dian)(dian)(dian)池(chi)進(jin)行連續(xu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，同時(shi)不會導致系統(tong)關斷，從而(er)縮(suo)短電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)間。

　　MAX8804是美信集成產(chan)品(pin)公(gong)司去(qu)年7月份推(tui)出的(de)(de)(de)充電(dian)(dian)器芯片(pian)，它采用了專門的(de)(de)(de)熱(re)調整電(dian)(dian)路(lu)，可以在(zai)快速(su)充電(dian)(dian)階段或系統處于高(gao)溫(wen)環(huan)境(jing)中(zhong)限(xian)制(zhi)裸片(pian)的(de)(de)(de)溫(wen)度。該充電(dian)(dian)器耐受30V的(de)(de)(de)直流輸入電(dian)(dian)壓(ya)(ya)，只占用6平方毫(hao)米的(de)(de)(de)電(dian)(dian)路(lu)板面積。另外，像TI公(gong)司提供的(de)(de)(de)1A bq24060充電(dian)(dian)器可提供熱(re)過載保(bao)護功能，允許器件在(zai)環(huan)境(jing)溫(wen)度很高(gao)的(de)(de)(de)惡劣環(huan)境(jing)中(zhong)連續(xu)運行，例如(ru)夏天的(de)(de)(de)汽車或不小心(xin)連接到具有較(jiao)高(gao)輸入電(dian)(dian)壓(ya)(ya)的(de)(de)(de)其它適配器。目前大多數(shu)較(jiao)新的(de)(de)(de)器件一般還會增(zeng)加過壓(ya)(ya)保(bao)護機制(zhi)。

　　多種電壓源

　　有個越(yue)(yue)來越(yue)(yue)常見的要(yao)求是從不(bu)同電(dian)壓源給電(dian)池(chi)充(chong)(chong)電(dian)，要(yao)點是在(zai)不(bu)使(shi)電(dian)壓源過(guo)(guo)載(zai)的情況下(xia)提供這個功(gong)能。可(ke)以通過(guo)(guo)在(zai)輸入(ru)條件(jian)改變(bian)時動態調整(zheng)充(chong)(chong)電(dian)電(dian)流實現這一功(gong)能。

　　舉例來(lai)說，移動用戶經(jing)常沒有(you)時間(jian)去找交流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)插座來(lai)給(gei)(gei)他(ta)們(men)的(de)(de)設(she)備(bei)充(chong)電(dian)(dian)(dian)(dian)(dian)，相反，他(ta)們(men)希望通過大多數電(dian)(dian)(dian)(dian)(dian)子(zi)設(she)備(bei)上(shang)都有(you)的(de)(de)眾多USB端口(kou)(kou)來(lai)給(gei)(gei)他(ta)們(men)的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)，包(bao)括其它(ta)電(dian)(dian)(dian)(dian)(dian)池(chi)供電(dian)(dian)(dian)(dian)(dian)的(de)(de)設(she)備(bei)，如筆記本電(dian)(dian)(dian)(dian)(dian)腦。因(yin)此(ci)，目(mu)前(qian)市(shi)場上(shang)的(de)(de)許多充(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)芯片支持從交流(liu)(liu)和USB輸入口(kou)(kou)給(gei)(gei)單節(jie)鋰電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)。此(ci)時的(de)(de)挑戰是(shi)補償USB端口(kou)(kou)提供的(de)(de)不斷變化的(de)(de)功率(lv)電(dian)(dian)(dian)(dian)(dian)平。隨著負載的(de)(de)變化，系統必須控制恒(heng)定(ding)的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)值以確保USB端口(kou)(kou)的(de)(de)正常操作。

　　一(yi)些充(chong)電(dian)(dian)器(qi)(qi)芯片利(li)用簡單(dan)的雙重方法支持(chi)USB操作，該方法使用兩個(ge)預設(she)的充(chong)電(dian)(dian)電(dian)(dian)流(liu)值(zhi)(通常(chang)是500mA和100mA)來支持(chi)USB端口(kou)允(yun)許的最(zui)大電(dian)(dian)流(liu)或必要時(shi)的最(zui)小電(dian)(dian)流(liu)以(yi)確保(bao)端口(kou)的完整性。通常(chang)這要求接口(kou)邏(luo)輯嵌入在充(chong)電(dian)(dian)器(qi)(qi)芯片中，以(yi)便系統微控制(zhi)器(qi)(qi)能夠連續(xu)讀取(qu)USB端口(kou)的狀態(tai)，并指示充(chong)電(dian)(dian)器(qi)(qi)從一(yi)個(ge)充(chong)電(dian)(dian)電(dian)(dian)流(liu)切換到另一(yi)個(ge)充(chong)電(dian)(dian)電(dian)(dian)流(liu)。

　　最近，有些充電(dian)(dian)器(qi)(qi)芯片制造商已經開發出能(neng)夠自(zi)動檢測(ce)USB端(duan)口的(de)可用(yong)(yong)功(gong)率、并據(ju)此調整充電(dian)(dian)電(dian)(dian)流來最大(da)化充電(dian)(dian)效率的(de)芯片。另外，許多充電(dian)(dian)器(qi)(qi)芯片不需要用(yong)(yong)戶干涉(she)，就(jiu)能(neng)夠自(zi)動檢測(ce)電(dian)(dian)源|穩(wen)壓器(qi)(qi)|穩(wen)壓器(qi)(qi)類型并調整它們的(de)充電(dian)(dian)過程。

　　當凌力爾特公(gong)司的LTC4075充電(dian)器芯片(pian)檢測(ce)到輸入端電(dian)源(yuan)(yuan)時，它(ta)能自動選擇(ze)合適(shi)的電(dian)源(yuan)(yuan)進行充電(dian)，同時不(bu)需(xu)要外接(jie)MOSFET、檢測(ce)電(dian)阻或(huo)阻流(liu)二(er)極管。Microchip Technology公(gong)司提供(gong)的MCP73837也能提供(gong)類似自動的電(dian)源(yuan)(yuan)選擇(ze)功(gong)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)的例子是AT3663，這是Advanced Analogic Technologies公司(AnalogicTech)提供(gong)的1A線性(xing)電池充電器系列(lie)芯片的第一個產(chan)品，可以(yi)用(yong)來(lai)給最多兩節串聯的鋰(li)離(li)子電池充電。AT3663采用(yong)該制造商的專有(you)模塊化BCD工藝技(ji)術(shu)制造。這種(zhong)工藝集成(cheng)了(le)完全隔離(li)的CMOS和高速互補雙(shuang)極晶體管(guan)以(yi)及30V DMOS功率(lv)器件(jian)，沒(mei)有(you)采用(yong)復雜而且昂貴的外延附生或高溫(wen)擴散技(ji)術(shu)。

　　上述新工藝允許AAT3663支持從4V到13.2V的(de)輸入電壓，因(yin)此設計師可以自由使用較低成本的(de)非(fei)穩壓適配器。