作為控制鋰離子充電狀態的功率器件，電池充電器芯(xin)片在便(bian)攜式系(xi)統設(she)(she)計中扮演著重要的角色。然而(er)，設(she)(she)計師們還在使(shi)用(yong)著從較老(lao)并且相對粗糙和低成本的充電(dian)器件、到(dao)較新(xin)的更復雜芯(xin)片等各種(zhong)各樣的器件，而(er)后者(zhe)集成了(le)越來越復雜的智(zhi)能，可以延長電(dian)池壽命(ming)，保護被充電(dian)系(xi)統不受損害(hai)。

　　安全第一

　　便攜(xie)式系統設計(ji)師面(mian)臨的(de)挑戰是：如何快(kuai)速高效地對系統進行(xing)充電(dian)(dian)(dian)(dian)，同時不影響用(yong)(yong)(yong)戶安(an)全(quan)或損壞電(dian)(dian)(dian)(dian)池(chi)(chi)，并且要(yao)占用(yong)(yong)(yong)最少的(de)電(dian)(dian)(dian)(dian)路板面(mian)積。鋰(li)離子充電(dian)(dian)(dian)(dian)器通(tong)常采用(yong)(yong)(yong)三種(zhong)充電(dian)(dian)(dian)(dian)模式來(lai)最大化(hua)充電(dian)(dian)(dian)(dian)效率并確保(bao)用(yong)(yong)(yong)戶安(an)全(quan)性。深(shen)度放電(dian)(dian)(dian)(dian)的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)必須先用(yong)(yong)(yong)較小的(de)電(dian)(dian)(dian)(dian)流進行(xing)逐步預充電(dian)(dian)(dian)(dian)，將電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓慢(man)慢(man)提升(sheng)到安(an)全(quan)閥值之上(shang)。

　　就拿工作電壓范圍是2.8V到4.2V的單節鋰離子電池充電器來說，它通常會測(ce)量(liang)被充(chong)(chong)電(dian)池(chi)的電(dian)壓，當電(dian)池(chi)電(dian)壓低(di)于3V時(shi)(shi)，它將進入預(yu)充(chong)(chong)或“慢充(chong)(chong)”模式(shi)。慢充(chong)(chong)模式(shi)可以在(zai)電(dian)池(chi)內阻很低(di)時(shi)(shi)防止(zhi)對(dui)電(dian)池(chi)高(gao)速(su)充(chong)(chong)電(dian)，從而盡量(liang)減(jian)少(shao)發(fa)熱。一般(ban)預(yu)充(chong)(chong)期間的充(chong)(chong)電(dian)速(su)率約是(shi)全速(su)充(chong)(chong)電(dian)時(shi)(shi)的10%。

　　圖1：Microchip科技公(gong)司的MCP73837雙輸(shu)入鋰離子(zi)/聚合物(wu)充(chong)(chong)電器(qi)具有電源選(xuan)擇功能，可以自動選(xuan)擇從交流或USB源進行充(chong)(chong)電。

　　一旦電(dian)(dian)(dian)池達到最小電(dian)(dian)(dian)壓(ya)值，充電(dian)(dian)(dian)器(qi)就切換到恒流(liu)或(huo)快充模(mo)式(shi)，此時將對電(dian)(dian)(dian)池全速充電(dian)(dian)(dian)，直(zhi)到電(dian)(dian)(dian)池達到接近滿(man)充電(dian)(dian)(dian)壓(ya)的第二個(ge)閥值。隨后充電(dian)(dian)(dian)器(qi)將進入(ru)恒壓(ya)模(mo)式(shi)，此時電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)保持(chi)不變，從(cong)而讓充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)逐漸停止(zhi)。當充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)小于(yu)預設的終止(zhi)閥值時，恒壓(ya)充電(dian)(dian)(dian)模(mo)式(shi)也就結束了。

　　熱管理是(shi)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)器(qi)設計師面臨的(de)(de)另一大挑戰。每個充(chong)電(dian)(dian)(dian)(dian)器(qi)芯片都會在(zai)充(chong)電(dian)(dian)(dian)(dian)過程中經歷(li)由于散熱引(yin)起(qi)的(de)(de)電(dian)(dian)(dian)(dian)壓下(xia)降。為了(le)避免電(dian)(dian)(dian)(dian)池(chi)(chi)損(sun)壞或系統關斷(duan)，大多數(shu)充(chong)電(dian)(dian)(dian)(dian)器(qi)都集成了(le)某種(zhong)(zhong)形式的(de)(de)控制機制來管理熱量累積(ji)。較(jiao)老的(de)(de)充(chong)電(dian)(dian)(dian)(dian)器(qi)芯片常采(cai)用“非彼即此”的(de)(de)方法來解決過熱或過流(liu)問題――當熱量達(da)(da)到(dao)預設的(de)(de)門限時(shi)它們將簡單(dan)地中斷(duan)充(chong)電(dian)(dian)(dian)(dian)過程。較(jiao)新的(de)(de)器(qi)件則采(cai)用更復雜的(de)(de)反(fan)饋技(ji)術連(lian)續監視裸片溫(wen)度，并(bing)以(yi)(yi)正比(bi)于環境溫(wen)度變化(hua)的(de)(de)速率動態(tai)或通(tong)過計算(suan)調整(zheng)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)。這種(zhong)(zhong)內置(zhi)智能允許(xu)當前的(de)(de)充(chong)電(dian)(dian)(dian)(dian)器(qi)芯片逐漸減少充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)，直到(dao)達(da)(da)到(dao)熱平衡(heng)，裸片溫(wen)度停止上升。這種(zhong)(zhong)技(ji)術能讓充(chong)電(dian)(dian)(dian)(dian)器(qi)以(yi)(yi)最大可能的(de)(de)電(dian)(dian)(dian)(dian)流(liu)對(dui)電(dian)(dian)(dian)(dian)池(chi)(chi)進行連(lian)續充(chong)電(dian)(dian)(dian)(dian)，同時(shi)不會導致系統關斷(duan)，從而(er)縮短電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)時(shi)間(jian)。

　　MAX8804是美信集成(cheng)產(chan)品公(gong)司去年7月(yue)份(fen)推(tui)出的(de)(de)(de)(de)充電(dian)器(qi)(qi)芯片，它(ta)采用了專(zhuan)門的(de)(de)(de)(de)熱調整電(dian)路，可以在快速充電(dian)階(jie)段或系統處于高溫環境中限制(zhi)裸片的(de)(de)(de)(de)溫度(du)(du)。該充電(dian)器(qi)(qi)耐受30V的(de)(de)(de)(de)直(zhi)流輸入電(dian)壓，只(zhi)占用6平(ping)方毫米的(de)(de)(de)(de)電(dian)路板面積。另外，像TI公(gong)司提(ti)供(gong)的(de)(de)(de)(de)1A bq24060充電(dian)器(qi)(qi)可提(ti)供(gong)熱過載保護功能，允許(xu)器(qi)(qi)件在環境溫度(du)(du)很高的(de)(de)(de)(de)惡(e)劣環境中連續運行，例如(ru)夏天(tian)的(de)(de)(de)(de)汽車或不小(xiao)心連接(jie)到(dao)具有(you)較高輸入電(dian)壓的(de)(de)(de)(de)其它(ta)適配器(qi)(qi)。目前大多數(shu)較新的(de)(de)(de)(de)器(qi)(qi)件一般還會增加過壓保護機(ji)制(zhi)。

　　多種電壓源

　　有(you)個越來(lai)越常(chang)見的(de)要(yao)求是從(cong)不同電壓(ya)源給(gei)電池(chi)充(chong)電，要(yao)點是在不使電壓(ya)源過(guo)(guo)載的(de)情況下提供這個功能。可以通(tong)過(guo)(guo)在輸入條件改變時動(dong)態調整充(chong)電電流實現這一(yi)功能。

　　舉例來說，移動用戶經常沒有時間(jian)去找交流電(dian)(dian)(dian)(dian)(dian)插座來給他(ta)們的(de)設(she)備(bei)(bei)(bei)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，相反(fan)，他(ta)們希望通過(guo)大(da)多(duo)(duo)數電(dian)(dian)(dian)(dian)(dian)子設(she)備(bei)(bei)(bei)上(shang)都有的(de)眾多(duo)(duo)USB端口來給他(ta)們的(de)電(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，包括其它電(dian)(dian)(dian)(dian)(dian)池供(gong)電(dian)(dian)(dian)(dian)(dian)的(de)設(she)備(bei)(bei)(bei)，如(ru)筆記本(ben)電(dian)(dian)(dian)(dian)(dian)腦(nao)。因此，目前市(shi)場上(shang)的(de)許多(duo)(duo)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器芯片支(zhi)持從(cong)交流和USB輸入口給單節鋰電(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)。此時的(de)挑戰是(shi)補償USB端口提(ti)供(gong)的(de)不(bu)斷(duan)變化的(de)功率(lv)電(dian)(dian)(dian)(dian)(dian)平。隨著負載的(de)變化，系統必須控制恒定的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流值以確(que)保USB端口的(de)正常操作。

　　一(yi)些充(chong)電(dian)(dian)器(qi)芯片(pian)利用(yong)簡單(dan)的雙重(zhong)方(fang)法支持USB操作，該方(fang)法使用(yong)兩(liang)個預(yu)設的充(chong)電(dian)(dian)電(dian)(dian)流值(通常是(shi)500mA和(he)100mA)來支持USB端(duan)口允許的最(zui)大電(dian)(dian)流或必要(yao)時的最(zui)小電(dian)(dian)流以(yi)確保端(duan)口的完整性。通常這要(yao)求接口邏輯(ji)嵌入在充(chong)電(dian)(dian)器(qi)芯片(pian)中，以(yi)便系統微(wei)控制器(qi)能夠連續讀取USB端(duan)口的狀(zhuang)態，并指(zhi)示充(chong)電(dian)(dian)器(qi)從一(yi)個充(chong)電(dian)(dian)電(dian)(dian)流切換(huan)到(dao)另(ling)一(yi)個充(chong)電(dian)(dian)電(dian)(dian)流。

　　最(zui)近，有些充(chong)電(dian)器芯片制造(zao)商已經開發(fa)出能夠自(zi)動檢測USB端口的(de)可(ke)用功率、并據此調(diao)整(zheng)充(chong)電(dian)電(dian)流來(lai)最(zui)大化充(chong)電(dian)效(xiao)率的(de)芯片。另外，許多充(chong)電(dian)器芯片不需要用戶干(gan)涉(she)，就能夠自(zi)動檢測電(dian)源類型并調(diao)整(zheng)它們的(de)充(chong)電(dian)過程。

　　當凌力爾特公(gong)司的LTC4075充電(dian)(dian)器芯片檢(jian)測(ce)到輸入(ru)端(duan)電(dian)(dian)源時，它(ta)能自動選(xuan)擇合(he)適(shi)的電(dian)(dian)源進(jin)行充電(dian)(dian)，同時不需要外接(jie)MOSFET、檢(jian)測(ce)電(dian)(dian)阻(zu)或阻(zu)流二極管。

　　Microchip Technology公司提(ti)供(gong)的MCP73837也(ye)能(neng)提(ti)供(gong)類似自動的電源選擇功能(neng)。

　　采用雙節電池

　　隨(sui)著便(bian)攜(xie)(xie)式系(xi)統設(she)計復雜性(xing)的(de)(de)提高，它們(men)使(shi)用的(de)(de)子(zi)系(xi)統、顯示(shi)器(qi)和(he)(he)處理器(qi)的(de)(de)數(shu)量(liang)與類型也越來越多(duo)，單節鋰離(li)(li)子(zi)電(dian)池(chi)已(yi)經(jing)無法(fa)滿足(zu)系(xi)統需要(yao)。因此，一(yi)(yi)些(xie)便(bian)攜(xie)(xie)式媒體播放器(qi)、高性(xing)能SLR型數(shu)碼(ma)相機(ji)和(he)(he)GPS導航系(xi)統都開始采(cai)用串聯的(de)(de)兩節鋰離(li)(li)子(zi)電(dian)池(chi)供電(dian)。這些(xie)便(bian)攜(xie)(xie)式產品一(yi)(yi)般要(yao)求(qiu)(qiu)輸入(ru)在8.4V和(he)(he)8.8V之間進行(xing)充電(dian)。設(she)計師以前都是使(shi)用分立器(qi)件實(shi)現(xian)這種設(she)計，但支持這個要(yao)求(qiu)(qiu)的(de)(de)新一(yi)(yi)代充電(dian)器(qi)芯(xin)片已(yi)經(jing)開始上市。

　　具有代表性(xing)的(de)(de)(de)例(li)子(zi)是AT3663，這是Advanced Analogic Technologies公司(AnalogicTech)提供的(de)(de)(de)1A線性(xing)電池充(chong)電器系(xi)列芯片(pian)的(de)(de)(de)第一個產品，可以用(yong)(yong)來給最多(duo)兩(liang)節串聯的(de)(de)(de)鋰離(li)子(zi)電池充(chong)電。AT3663采用(yong)(yong)該制(zhi)造(zao)商的(de)(de)(de)專有模(mo)塊化BCD工藝技(ji)術制(zhi)造(zao)。這種工藝集成了完(wan)全隔離(li)的(de)(de)(de)CMOS和高(gao)速(su)互補雙極晶體(ti)管以及30V DMOS功率器件，沒有采用(yong)(yong)復雜而且(qie)昂(ang)貴的(de)(de)(de)外(wai)延(yan)附生或高(gao)溫(wen)擴散技(ji)術。

　　上述新工(gong)藝允許AAT3663支持從4V到13.2V的輸(shu)入電壓，因此設計師(shi)可以自由(you)使用較低成本的非穩壓適配(pei)器。