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(huan)沒有達(da)成(cheng)一個同樣統(tong)一的(de)(de)(de)意見。作為(wei)控制鋰離子充(chong)(chong)電(dian)狀態的(de)(de)(de)功率器(qi)件(jian)，電(dian)池充(chong)(chong)電(dian)器(qi)芯(xin)片(pian)在便攜式系統(tong)設(she)計(ji)中扮(ban)演著重要的(de)(de)(de)角色。然(ran)而(er)，設(she)計(ji)師們還(huan)在使用著從較(jiao)老并且相對粗(cu)糙和低成(cheng)本的(de)(de)(de)充(chong)(chong)電(dian)器(qi)件(jian)、到較(jiao)新的(de)(de)(de)更(geng)復雜(za)芯(xin)片(pian)等(deng)各種各樣的(de)(de)(de)器(qi)件(jian)，而(er)后者(zhe)集(ji)成(cheng)了越(yue)(yue)來越(yue)(yue)復雜(za)的(de)(de)(de)智能，可以延長電(dian)池壽命(ming)，保護(hu)被充(chong)(chong)電(dian)系統(tong)不受(shou)損害。

　　安全第一

　　便攜式系(xi)統設計師面臨(lin)的挑戰是：如何(he)快速高效(xiao)(xiao)地(di)對系(xi)統進行充(chong)電(dian)，同時不影響用(yong)(yong)戶安全或損(sun)壞電(dian)池，并(bing)且要占用(yong)(yong)最少的電(dian)路板面積。鋰離子(zi)充(chong)電(dian)器通常采用(yong)(yong)三(san)種(zhong)充(chong)電(dian)模式來(lai)最大化充(chong)電(dian)效(xiao)(xiao)率并(bing)確(que)保用(yong)(yong)戶安全性。深度放電(dian)的電(dian)池必須先(xian)用(yong)(yong)較小的電(dian)流進行逐步預充(chong)電(dian)，將電(dian)池電(dian)壓慢(man)慢(man)提升到安全閥值之上(shang)。

　　就拿工作(zuo)電(dian)(dian)(dian)(dian)壓(ya)范圍是2.8V到(dao)4.2V的(de)(de)單節鋰離子電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)器(qi)來說，它(ta)通常會測量被(bei)充(chong)電(dian)(dian)(dian)(dian)池(chi)的(de)(de)電(dian)(dian)(dian)(dian)壓(ya)，當電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(ya)低(di)(di)于(yu)3V時，它(ta)將進入預充(chong)或“慢(man)(man)充(chong)”模式。慢(man)(man)充(chong)模式可以在電(dian)(dian)(dian)(dian)池(chi)內阻很低(di)(di)時防(fang)止對電(dian)(dian)(dian)(dian)池(chi)高(gao)速(su)(su)充(chong)電(dian)(dian)(dian)(dian)，從而盡量減少發熱(re)。一般預充(chong)期間的(de)(de)充(chong)電(dian)(dian)(dian)(dian)速(su)(su)率(lv)約是全速(su)(su)充(chong)電(dian)(dian)(dian)(dian)時的(de)(de)10%。

　　一旦電池達到最小電壓值，充電器就(jiu)切換到恒流或快(kuai)充模(mo)式，此時將對電(dian)(dian)(dian)(dian)池全速充電(dian)(dian)(dian)(dian)，直到電(dian)(dian)(dian)(dian)池達到接近滿充電(dian)(dian)(dian)(dian)壓(ya)的第二個閥值。隨后充電(dian)(dian)(dian)(dian)器將進入恒壓(ya)模(mo)式，此時電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)保持(chi)不變，從而讓(rang)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流逐漸停止(zhi)。當充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流小于預設的終止(zhi)閥值時，恒壓(ya)充電(dian)(dian)(dian)(dian)模(mo)式也就(jiu)結束了。

　　熱(re)管理(li)是電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)器(qi)設計師面臨的(de)(de)另一大(da)挑戰。每個充(chong)電(dian)(dian)(dian)(dian)器(qi)芯(xin)(xin)片都會在充(chong)電(dian)(dian)(dian)(dian)過程中(zhong)經(jing)歷由于(yu)散熱(re)引起的(de)(de)電(dian)(dian)(dian)(dian)壓(ya)下(xia)降。為(wei)了(le)避免(mian)電(dian)(dian)(dian)(dian)池(chi)損壞或(huo)系(xi)(xi)統關斷，大(da)多數充(chong)電(dian)(dian)(dian)(dian)器(qi)都集成了(le)某(mou)種形式(shi)的(de)(de)控(kong)制機制來管理(li)熱(re)量(liang)累積。較老的(de)(de)充(chong)電(dian)(dian)(dian)(dian)器(qi)芯(xin)(xin)片常采(cai)用(yong)“非彼即此”的(de)(de)方(fang)法來解(jie)決過熱(re)或(huo)過流問題――當熱(re)量(liang)達到預(yu)設的(de)(de)門限時(shi)它們(men)將簡單地中(zhong)斷充(chong)電(dian)(dian)(dian)(dian)過程。較新的(de)(de)器(qi)件則采(cai)用(yong)更復雜的(de)(de)反饋技(ji)術連續(xu)監視裸(luo)片溫(wen)(wen)度(du)(du)，并以(yi)正比于(yu)環境(jing)溫(wen)(wen)度(du)(du)變化(hua)的(de)(de)速率動態或(huo)通(tong)過計算調整充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流。這種內置智(zhi)能(neng)允許當前的(de)(de)充(chong)電(dian)(dian)(dian)(dian)器(qi)芯(xin)(xin)片逐漸減少(shao)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流，直到達到熱(re)平衡，裸(luo)片溫(wen)(wen)度(du)(du)停止(zhi)上升(sheng)。這種技(ji)術能(neng)讓(rang)充(chong)電(dian)(dian)(dian)(dian)器(qi)以(yi)最大(da)可能(neng)的(de)(de)電(dian)(dian)(dian)(dian)流對(dui)電(dian)(dian)(dian)(dian)池(chi)進行連續(xu)充(chong)電(dian)(dian)(dian)(dian)，同時(shi)不會導致系(xi)(xi)統關斷，從而(er)縮(suo)短電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)時(shi)間。

　　MAX8804是美信(xin)集成產品公司去年(nian)7月份推出的(de)充(chong)電(dian)(dian)器(qi)(qi)芯(xin)片，它(ta)采用了(le)專門(men)的(de)熱調整電(dian)(dian)路，可以在快(kuai)速充(chong)電(dian)(dian)階(jie)段或系統處于高溫環(huan)(huan)境(jing)(jing)中(zhong)限(xian)制(zhi)裸(luo)片的(de)溫度。該(gai)充(chong)電(dian)(dian)器(qi)(qi)耐受30V的(de)直流輸入電(dian)(dian)壓(ya)，只占用6平方毫米的(de)電(dian)(dian)路板面積。另(ling)外(wai)，像TI公司提供(gong)的(de)1A bq24060充(chong)電(dian)(dian)器(qi)(qi)可提供(gong)熱過(guo)載保護功能，允許器(qi)(qi)件在環(huan)(huan)境(jing)(jing)溫度很高的(de)惡劣環(huan)(huan)境(jing)(jing)中(zhong)連續運行(xing)，例如(ru)夏天(tian)的(de)汽車或不(bu)小心連接到具有(you)較(jiao)高輸入電(dian)(dian)壓(ya)的(de)其它(ta)適配器(qi)(qi)。目前(qian)大多(duo)數較(jiao)新的(de)器(qi)(qi)件一般還會增加過(guo)壓(ya)保護機制(zhi)。

　　多種電壓源

　　有個(ge)越來越常見的要(yao)求是(shi)從不(bu)同電(dian)壓(ya)源(yuan)給電(dian)池充(chong)電(dian)，要(yao)點是(shi)在不(bu)使電(dian)壓(ya)源(yuan)過載(zai)的情況下提供這個(ge)功(gong)能(neng)。可以通過在輸(shu)入條件改(gai)變時動態調整充(chong)電(dian)電(dian)流實現這一功(gong)能(neng)。

　　舉例來(lai)說，移動用(yong)戶經常沒有(you)時間去找交流電(dian)(dian)插座來(lai)給(gei)他(ta)們(men)的(de)(de)(de)設備(bei)充(chong)(chong)(chong)電(dian)(dian)，相反，他(ta)們(men)希望通過大多數電(dian)(dian)子設備(bei)上都有(you)的(de)(de)(de)眾多USB端(duan)口(kou)(kou)(kou)來(lai)給(gei)他(ta)們(men)的(de)(de)(de)電(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)，包括其它電(dian)(dian)池(chi)供(gong)(gong)電(dian)(dian)的(de)(de)(de)設備(bei)，如筆記本電(dian)(dian)腦。因(yin)此，目(mu)前(qian)市場(chang)上的(de)(de)(de)許多充(chong)(chong)(chong)電(dian)(dian)器芯片支(zhi)持(chi)從交流和USB輸入口(kou)(kou)(kou)給(gei)單節(jie)鋰電(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)。此時的(de)(de)(de)挑戰(zhan)是補償USB端(duan)口(kou)(kou)(kou)提(ti)供(gong)(gong)的(de)(de)(de)不斷變化(hua)的(de)(de)(de)功率電(dian)(dian)平。隨著負載(zai)的(de)(de)(de)變化(hua)，系統必須控制恒定(ding)的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流值以(yi)確保USB端(duan)口(kou)(kou)(kou)的(de)(de)(de)正常操作。

　　一(yi)些(xie)充電(dian)器(qi)(qi)芯片利用簡單(dan)的(de)雙重方(fang)法支(zhi)持USB操作，該方(fang)法使用兩個(ge)預設(she)的(de)充電(dian)電(dian)流(liu)(liu)值(通常(chang)是500mA和100mA)來支(zhi)持USB端(duan)口(kou)允許的(de)最(zui)大(da)電(dian)流(liu)(liu)或必要時的(de)最(zui)小電(dian)流(liu)(liu)以確(que)保端(duan)口(kou)的(de)完整性。通常(chang)這要求(qiu)接口(kou)邏輯嵌(qian)入在充電(dian)器(qi)(qi)芯片中，以便系(xi)統微控制器(qi)(qi)能(neng)夠連續讀取USB端(duan)口(kou)的(de)狀態，并指示充電(dian)器(qi)(qi)從(cong)一(yi)個(ge)充電(dian)電(dian)流(liu)(liu)切(qie)換(huan)到另一(yi)個(ge)充電(dian)電(dian)流(liu)(liu)。

　　最近，有(you)些充電(dian)(dian)(dian)(dian)器(qi)芯(xin)片(pian)(pian)制造商已經開發出能夠自動檢測USB端口的可用功率、并據此調(diao)整充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流來最大化充電(dian)(dian)(dian)(dian)效率的芯(xin)片(pian)(pian)。另外(wai)，許多充電(dian)(dian)(dian)(dian)器(qi)芯(xin)片(pian)(pian)不需要用戶干(gan)涉，就(jiu)能夠自動檢測電(dian)(dian)(dian)(dian)源|穩(wen)壓器(qi)|穩(wen)壓器(qi)類型并調(diao)整它(ta)們的充電(dian)(dian)(dian)(dian)過程。

　　當凌力(li)爾(er)特公(gong)司的(de)LTC4075充電(dian)(dian)器芯(xin)片檢(jian)測到輸入端電(dian)(dian)源(yuan)時(shi)，它能(neng)自動選擇(ze)合適的(de)電(dian)(dian)源(yuan)進(jin)行充電(dian)(dian)，同(tong)時(shi)不(bu)需要外接MOSFET、檢(jian)測電(dian)(dian)阻或阻流二極(ji)管。Microchip Technology公(gong)司提供的(de)MCP73837也能(neng)提供類似自動的(de)電(dian)(dian)源(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(biao)性的(de)例子是AT3663，這(zhe)是Advanced Analogic Technologies公司(si)(AnalogicTech)提供(gong)的(de)1A線性電(dian)(dian)池充電(dian)(dian)器(qi)系列芯片的(de)第一個產品(pin)，可以用來(lai)給最多兩節(jie)串聯的(de)鋰離子電(dian)(dian)池充電(dian)(dian)。AT3663采用該制(zhi)造商的(de)專有(you)(you)模塊(kuai)化BCD工(gong)藝技術制(zhi)造。這(zhe)種工(gong)藝集成了完(wan)全隔(ge)離的(de)CMOS和(he)高(gao)速互補(bu)雙極晶體管以及30V DMOS功率器(qi)件，沒有(you)(you)采用復(fu)雜而且昂(ang)貴的(de)外(wai)延附生或高(gao)溫擴散技術。

　　上(shang)述(shu)新工藝(yi)允許AAT3663支持從4V到13.2V的(de)輸入電(dian)壓，因此設計師可以自由使(shi)用較(jiao)低成本(ben)的(de)非(fei)穩壓適配器。