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)片還沒有達成一個(ge)同樣統一的(de)意見(jian)。作為控制鋰(li)離子充電(dian)狀(zhuang)態(tai)的(de)功率器件(jian)，電(dian)池(chi)充電(dian)器芯(xin)片在(zai)便攜式系統設計中(zhong)扮演(yan)著重要的(de)角色。然而(er)(er)，設計師們還在(zai)使用著從(cong)較(jiao)老(lao)并(bing)且相對粗(cu)糙和低成本的(de)充電(dian)器件(jian)、到較(jiao)新的(de)更(geng)復(fu)雜芯(xin)片等各種各樣的(de)器件(jian)，而(er)(er)后者(zhe)集成了越來越復(fu)雜的(de)智能，可以(yi)延(yan)長電(dian)池(chi)壽命，保(bao)護被充電(dian)系統不受損害。

　　安全第一

　　便攜式系(xi)統設計師面(mian)(mian)臨的挑(tiao)戰是(shi)：如何(he)快速高效地對系(xi)統進行充電(dian)(dian)(dian)，同時不(bu)影響用(yong)(yong)戶(hu)安(an)全(quan)(quan)或損壞電(dian)(dian)(dian)池，并且要(yao)占用(yong)(yong)最少的電(dian)(dian)(dian)路(lu)板面(mian)(mian)積。鋰(li)離子(zi)充電(dian)(dian)(dian)器(qi)通常采用(yong)(yong)三種充電(dian)(dian)(dian)模式來(lai)最大化充電(dian)(dian)(dian)效率并確保用(yong)(yong)戶(hu)安(an)全(quan)(quan)性。深度(du)放電(dian)(dian)(dian)的電(dian)(dian)(dian)池必須先用(yong)(yong)較(jiao)小的電(dian)(dian)(dian)流進行逐步預充電(dian)(dian)(dian)，將電(dian)(dian)(dian)池電(dian)(dian)(dian)壓慢(man)(man)慢(man)(man)提升到安(an)全(quan)(quan)閥(fa)值(zhi)之上(shang)。

　　就拿工(gong)作(zuo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓范圍是(shi)2.8V到4.2V的(de)單節(jie)鋰離子電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)來說，它通常(chang)會測量被充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓低(di)(di)于3V時(shi)，它將進入(ru)預(yu)充或“慢(man)充”模式(shi)。慢(man)充模式(shi)可(ke)以在電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)內阻很低(di)(di)時(shi)防止對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)高速充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，從而(er)盡量減少發(fa)熱。一般預(yu)充期間的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)速率(lv)約是(shi)全速充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)的(de)10%。

　　一旦電池達到最小電壓值，充電器就(jiu)切(qie)換(huan)到(dao)恒(heng)(heng)流(liu)或(huo)快(kuai)充模(mo)式，此(ci)時(shi)將對電(dian)(dian)(dian)(dian)(dian)池(chi)全速充電(dian)(dian)(dian)(dian)(dian)，直到(dao)電(dian)(dian)(dian)(dian)(dian)池(chi)達到(dao)接近滿充電(dian)(dian)(dian)(dian)(dian)壓的第二個閥值(zhi)。隨后充電(dian)(dian)(dian)(dian)(dian)器將進(jin)入恒(heng)(heng)壓模(mo)式，此(ci)時(shi)電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓保持不(bu)變，從而(er)讓充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)逐漸停止。當充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)小于預設的終止閥值(zhi)時(shi)，恒(heng)(heng)壓充電(dian)(dian)(dian)(dian)(dian)模(mo)式也就(jiu)結束了(le)。

　　熱管(guan)理是電(dian)(dian)池充(chong)(chong)(chong)(chong)電(dian)(dian)器(qi)(qi)(qi)設計師面臨的(de)另一大挑戰。每(mei)個充(chong)(chong)(chong)(chong)電(dian)(dian)器(qi)(qi)(qi)芯片(pian)(pian)都(dou)會在(zai)充(chong)(chong)(chong)(chong)電(dian)(dian)過(guo)程中經歷(li)由于(yu)(yu)散(san)熱引起的(de)電(dian)(dian)壓下降。為了避(bi)免電(dian)(dian)池損壞(huai)或系(xi)統(tong)關斷(duan)，大多數充(chong)(chong)(chong)(chong)電(dian)(dian)器(qi)(qi)(qi)都(dou)集(ji)成了某種形式的(de)控制機制來管(guan)理熱量(liang)累(lei)積。較(jiao)老的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)器(qi)(qi)(qi)芯片(pian)(pian)常采用(yong)“非(fei)彼(bi)即此”的(de)方法來解決過(guo)熱或過(guo)流(liu)問題(ti)――當(dang)熱量(liang)達到預設的(de)門限時它們將簡單地(di)中斷(duan)充(chong)(chong)(chong)(chong)電(dian)(dian)過(guo)程。較(jiao)新的(de)器(qi)(qi)(qi)件則采用(yong)更(geng)復雜的(de)反饋技術(shu)連續監(jian)視(shi)裸片(pian)(pian)溫(wen)(wen)度，并以正(zheng)比于(yu)(yu)環境溫(wen)(wen)度變化(hua)的(de)速率(lv)動態(tai)或通(tong)過(guo)計算調整充(chong)(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)。這種內置智能允許當(dang)前的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)器(qi)(qi)(qi)芯片(pian)(pian)逐漸減(jian)少充(chong)(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)，直到達到熱平(ping)衡，裸片(pian)(pian)溫(wen)(wen)度停止上升。這種技術(shu)能讓充(chong)(chong)(chong)(chong)電(dian)(dian)器(qi)(qi)(qi)以最大可能的(de)電(dian)(dian)流(liu)對電(dian)(dian)池進行連續充(chong)(chong)(chong)(chong)電(dian)(dian)，同(tong)時不會導致系(xi)統(tong)關斷(duan)，從(cong)而縮短(duan)電(dian)(dian)池充(chong)(chong)(chong)(chong)電(dian)(dian)時間。

　　MAX8804是美信集成產品(pin)公(gong)司去年7月份推出的(de)(de)充電(dian)器芯(xin)片，它(ta)采用了專(zhuan)門的(de)(de)熱調(diao)整電(dian)路(lu)，可以在(zai)快速充電(dian)階段或(huo)系統處于高溫環(huan)(huan)境(jing)中限制(zhi)裸片的(de)(de)溫度。該(gai)充電(dian)器耐受30V的(de)(de)直(zhi)流輸(shu)入電(dian)壓(ya)，只占(zhan)用6平方毫米的(de)(de)電(dian)路(lu)板面積(ji)。另外，像(xiang)TI公(gong)司提供(gong)的(de)(de)1A bq24060充電(dian)器可提供(gong)熱過(guo)載(zai)保護功能，允許器件在(zai)環(huan)(huan)境(jing)溫度很高的(de)(de)惡劣環(huan)(huan)境(jing)中連續運行，例如(ru)夏天的(de)(de)汽車(che)或(huo)不小心連接到具(ju)有較高輸(shu)入電(dian)壓(ya)的(de)(de)其(qi)它(ta)適配器。目前大多數(shu)較新的(de)(de)器件一般還會增加過(guo)壓(ya)保護機制(zhi)。

　　多種電壓源

　　有個越來越常見的要求是從不同電(dian)壓源給電(dian)池充(chong)電(dian)，要點是在(zai)不使電(dian)壓源過載的情況下提(ti)供這(zhe)個功能(neng)。可以通過在(zai)輸入條(tiao)件改(gai)變時(shi)動態調整(zheng)充(chong)電(dian)電(dian)流實現這(zhe)一(yi)功能(neng)。

　　舉例(li)來說，移動用戶經常沒有時(shi)間去找交(jiao)流電(dian)(dian)(dian)(dian)(dian)插(cha)座來給(gei)他(ta)(ta)(ta)們的(de)(de)(de)設備(bei)(bei)充電(dian)(dian)(dian)(dian)(dian)，相反(fan)，他(ta)(ta)(ta)們希望通過(guo)大多數電(dian)(dian)(dian)(dian)(dian)子設備(bei)(bei)上(shang)都(dou)有的(de)(de)(de)眾(zhong)多USB端口(kou)來給(gei)他(ta)(ta)(ta)們的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)，包括其(qi)它電(dian)(dian)(dian)(dian)(dian)池(chi)供電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)設備(bei)(bei)，如筆記本(ben)電(dian)(dian)(dian)(dian)(dian)腦。因(yin)此(ci)，目前(qian)市(shi)場上(shang)的(de)(de)(de)許多充電(dian)(dian)(dian)(dian)(dian)器芯片(pian)支持從交(jiao)流和USB輸(shu)入口(kou)給(gei)單節鋰電(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)。此(ci)時(shi)的(de)(de)(de)挑戰是(shi)補償USB端口(kou)提(ti)供的(de)(de)(de)不斷變化(hua)的(de)(de)(de)功率電(dian)(dian)(dian)(dian)(dian)平。隨(sui)著負載的(de)(de)(de)變化(hua)，系統必須(xu)控制恒定的(de)(de)(de)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流值以確(que)保USB端口(kou)的(de)(de)(de)正常操作。

　　一些充(chong)(chong)電(dian)(dian)(dian)器芯片(pian)利用簡單(dan)的(de)雙重方法(fa)支(zhi)持USB操作(zuo)，該方法(fa)使用兩個預設的(de)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)(liu)值(通常是500mA和100mA)來支(zhi)持USB端(duan)口(kou)(kou)允許的(de)最大電(dian)(dian)(dian)流(liu)(liu)(liu)或必要時的(de)最小(xiao)電(dian)(dian)(dian)流(liu)(liu)(liu)以(yi)確保端(duan)口(kou)(kou)的(de)完整性。通常這(zhe)要求接口(kou)(kou)邏輯嵌(qian)入在充(chong)(chong)電(dian)(dian)(dian)器芯片(pian)中，以(yi)便系(xi)統微控制器能(neng)夠連續讀(du)取USB端(duan)口(kou)(kou)的(de)狀態，并(bing)指(zhi)示充(chong)(chong)電(dian)(dian)(dian)器從一個充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)(liu)切換(huan)到另一個充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)(liu)。

　　最(zui)(zui)近(jin)，有些充(chong)電(dian)(dian)器芯(xin)片(pian)制造商已經開發出(chu)能夠自動(dong)檢測USB端口的(de)可用(yong)功率(lv)、并據此調(diao)整充(chong)電(dian)(dian)電(dian)(dian)流來最(zui)(zui)大(da)化充(chong)電(dian)(dian)效率(lv)的(de)芯(xin)片(pian)。另外，許多充(chong)電(dian)(dian)器芯(xin)片(pian)不(bu)需要用(yong)戶干涉，就能夠自動(dong)檢測電(dian)(dian)源|穩(wen)壓(ya)器|穩(wen)壓(ya)器類型并調(diao)整它們(men)的(de)充(chong)電(dian)(dian)過(guo)程。

　　當凌力爾特公(gong)司(si)的(de)LTC4075充(chong)電器芯片檢測(ce)到(dao)輸入(ru)端電源(yuan)時，它能自動選擇合適的(de)電源(yuan)進行充(chong)電，同時不需(xu)要外接MOSFET、檢測(ce)電阻(zu)(zu)或阻(zu)(zu)流(liu)二極(ji)管(guan)。Microchip Technology公(gong)司(si)提(ti)供(gong)的(de)MCP73837也能提(ti)供(gong)類似自動的(de)電源(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。

　　具有代表(biao)性(xing)的(de)例(li)子是AT3663，這(zhe)是Advanced Analogic Technologies公司(AnalogicTech)提供的(de)1A線性(xing)電池充電器(qi)系列芯片(pian)的(de)第一個產品，可以用(yong)來(lai)給(gei)最多兩節串(chuan)聯(lian)的(de)鋰(li)離子電池充電。AT3663采(cai)用(yong)該制(zhi)造商的(de)專有模塊化BCD工藝(yi)技術制(zhi)造。這(zhe)種工藝(yi)集成了完全隔離的(de)CMOS和高(gao)速互補(bu)雙極晶體(ti)管以及30V DMOS功率器(qi)件，沒有采(cai)用(yong)復雜而且(qie)昂貴(gui)的(de)外(wai)延附生(sheng)或高(gao)溫擴散技術。

　　上述新(xin)工藝允許AAT3663支(zhi)持從4V到(dao)13.2V的輸入電壓，因此設計師可(ke)以(yi)自由使用較低成本的非(fei)穩壓適配(pei)器。