作為控制鋰離子充電狀態的功率器件，電池充電器芯片在便攜式(shi)系統設計中扮演著(zhu)重(zhong)要的(de)(de)角色(se)。然而，設計師們還在使用著(zhu)從較老并且相(xiang)對粗糙和(he)低成(cheng)本的(de)(de)充電器(qi)件(jian)、到較新的(de)(de)更復(fu)雜芯片等各種各樣的(de)(de)器(qi)件(jian)，而后者集成(cheng)了越(yue)(yue)來越(yue)(yue)復(fu)雜的(de)(de)智(zhi)能，可以延長電池壽命，保護被(bei)充電系統不受損(sun)害。

　　安全第一

　　便攜式系(xi)(xi)統設計(ji)師面臨的(de)挑(tiao)戰是：如(ru)何(he)快速高效(xiao)地對系(xi)(xi)統進行充(chong)電(dian)(dian)，同(tong)時(shi)不影響用戶安全(quan)或損(sun)壞電(dian)(dian)池(chi)，并且要(yao)占用最少的(de)電(dian)(dian)路板(ban)面積。鋰離子充(chong)電(dian)(dian)器通常(chang)采用三種充(chong)電(dian)(dian)模式來最大化充(chong)電(dian)(dian)效(xiao)率并確(que)保用戶安全(quan)性。深度放(fang)電(dian)(dian)的(de)電(dian)(dian)池(chi)必(bi)須先用較小的(de)電(dian)(dian)流進行逐步(bu)預充(chong)電(dian)(dian)，將電(dian)(dian)池(chi)電(dian)(dian)壓慢慢提升到安全(quan)閥(fa)值(zhi)之(zhi)上。

　　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，它通常會測量(liang)被充(chong)(chong)(chong)電(dian)(dian)池的(de)電(dian)(dian)壓，當電(dian)(dian)池電(dian)(dian)壓低于3V時(shi)(shi)，它將進入預(yu)充(chong)(chong)(chong)或“慢充(chong)(chong)(chong)”模(mo)式。慢充(chong)(chong)(chong)模(mo)式可(ke)以在電(dian)(dian)池內阻很低時(shi)(shi)防止對電(dian)(dian)池高速(su)充(chong)(chong)(chong)電(dian)(dian)，從而盡量(liang)減(jian)少發熱。一般預(yu)充(chong)(chong)(chong)期間的(de)充(chong)(chong)(chong)電(dian)(dian)速(su)率約(yue)是全速(su)充(chong)(chong)(chong)電(dian)(dian)時(shi)(shi)的(de)10%。

　　圖1：Microchip科技公司(si)的(de)MCP73837雙輸入鋰離子/聚合物充電(dian)器(qi)具有電(dian)源(yuan)選擇(ze)功能，可以(yi)自動選擇(ze)從交(jiao)流(liu)或USB源(yuan)進行(xing)充電(dian)。

　　一(yi)旦電(dian)(dian)(dian)(dian)池達(da)(da)到(dao)(dao)最小電(dian)(dian)(dian)(dian)壓(ya)(ya)值，充(chong)(chong)電(dian)(dian)(dian)(dian)器就切換(huan)到(dao)(dao)恒(heng)流或快(kuai)充(chong)(chong)模(mo)式，此時將對電(dian)(dian)(dian)(dian)池全(quan)速充(chong)(chong)電(dian)(dian)(dian)(dian)，直(zhi)到(dao)(dao)電(dian)(dian)(dian)(dian)池達(da)(da)到(dao)(dao)接(jie)近滿充(chong)(chong)電(dian)(dian)(dian)(dian)壓(ya)(ya)的第二(er)個(ge)閥值。隨后充(chong)(chong)電(dian)(dian)(dian)(dian)器將進入恒(heng)壓(ya)(ya)模(mo)式，此時電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)(ya)保持不(bu)變，從而(er)讓充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流逐(zhu)漸停止(zhi)(zhi)。當(dang)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流小于(yu)預(yu)設的終(zhong)止(zhi)(zhi)閥值時，恒(heng)壓(ya)(ya)充(chong)(chong)電(dian)(dian)(dian)(dian)模(mo)式也就結(jie)束了。

　　熱管理是電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器設(she)計師(shi)面臨(lin)的(de)(de)(de)另一大挑戰。每個充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器芯片(pian)(pian)都會在(zai)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)過(guo)程中經歷(li)由于散熱引起的(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya)下(xia)降。為了避免電(dian)(dian)(dian)(dian)池(chi)損壞或(huo)系統(tong)(tong)關(guan)斷，大多(duo)數充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器都集成了某種(zhong)(zhong)形式的(de)(de)(de)控制機(ji)制來管理熱量(liang)累積。較老(lao)的(de)(de)(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器芯片(pian)(pian)常采(cai)用(yong)“非(fei)彼即此”的(de)(de)(de)方法(fa)來解決過(guo)熱或(huo)過(guo)流問題――當(dang)熱量(liang)達到(dao)預(yu)設(she)的(de)(de)(de)門限時(shi)它們將(jiang)簡(jian)單地(di)中斷充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)過(guo)程。較新的(de)(de)(de)器件則(ze)采(cai)用(yong)更復雜的(de)(de)(de)反(fan)饋技術(shu)連續監(jian)視裸片(pian)(pian)溫(wen)度(du)，并以(yi)正(zheng)比于環境溫(wen)度(du)變化的(de)(de)(de)速率動態或(huo)通過(guo)計算調整充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流。這種(zhong)(zhong)內置(zhi)智能允許當(dang)前(qian)的(de)(de)(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器芯片(pian)(pian)逐漸減少充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流，直到(dao)達到(dao)熱平衡，裸片(pian)(pian)溫(wen)度(du)停止上升。這種(zhong)(zhong)技術(shu)能讓充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器以(yi)最大可能的(de)(de)(de)電(dian)(dian)(dian)(dian)流對電(dian)(dian)(dian)(dian)池(chi)進行連續充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)，同(tong)時(shi)不(bu)會導致系統(tong)(tong)關(guan)斷，從(cong)而縮短電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)間(jian)。

　　MAX8804是(shi)美信集成產品公司去年7月份(fen)推出的(de)充(chong)電(dian)器(qi)芯片，它采(cai)用了專門(men)的(de)熱調整電(dian)路(lu)，可(ke)以在快速充(chong)電(dian)階段或(huo)系統處于高溫(wen)環(huan)境(jing)(jing)中(zhong)限制裸片的(de)溫(wen)度(du)。該充(chong)電(dian)器(qi)耐受30V的(de)直流輸入電(dian)壓(ya)，只占用6平方毫米的(de)電(dian)路(lu)板(ban)面積。另外，像TI公司提(ti)供的(de)1A bq24060充(chong)電(dian)器(qi)可(ke)提(ti)供熱過載保護功能(neng)，允許器(qi)件(jian)在環(huan)境(jing)(jing)溫(wen)度(du)很高的(de)惡(e)劣環(huan)境(jing)(jing)中(zhong)連續運行，例如夏天(tian)的(de)汽車或(huo)不小心連接到具有較高輸入電(dian)壓(ya)的(de)其它適(shi)配器(qi)。目前(qian)大多(duo)數較新的(de)器(qi)件(jian)一般還會增加(jia)過壓(ya)保護機制。

　　多種電壓源

　　有個越來越常見的(de)要求(qiu)是從(cong)不同電(dian)(dian)壓源(yuan)給電(dian)(dian)池充電(dian)(dian)，要點是在不使(shi)電(dian)(dian)壓源(yuan)過(guo)載的(de)情況下提(ti)供這個功能(neng)。可以通過(guo)在輸入條件改(gai)變時動態調(diao)整充電(dian)(dian)電(dian)(dian)流實(shi)現這一功能(neng)。

　　舉(ju)例(li)來說(shuo)，移動用戶經(jing)常沒有時(shi)(shi)間去找交流電(dian)(dian)(dian)插座來給他們(men)的(de)設(she)備(bei)充電(dian)(dian)(dian)，相反(fan)，他們(men)希望(wang)通過大多(duo)數(shu)電(dian)(dian)(dian)子設(she)備(bei)上都(dou)有的(de)眾多(duo)USB端口(kou)來給他們(men)的(de)電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)，包括其它電(dian)(dian)(dian)池(chi)供電(dian)(dian)(dian)的(de)設(she)備(bei)，如筆記本電(dian)(dian)(dian)腦。因此，目前市(shi)場上的(de)許多(duo)充電(dian)(dian)(dian)器芯(xin)片支持(chi)從交流和(he)USB輸入(ru)口(kou)給單節鋰電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)。此時(shi)(shi)的(de)挑戰(zhan)是補(bu)償USB端口(kou)提供的(de)不斷變化(hua)的(de)功率(lv)電(dian)(dian)(dian)平。隨(sui)著負載的(de)變化(hua)，系統必須控制恒(heng)定的(de)充電(dian)(dian)(dian)電(dian)(dian)(dian)流值(zhi)以(yi)確保USB端口(kou)的(de)正常操作。

　　一(yi)些充(chong)(chong)電(dian)(dian)(dian)器芯片利用(yong)簡單的(de)(de)(de)雙重方法(fa)支持(chi)USB操作(zuo)，該方法(fa)使用(yong)兩(liang)個預設的(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)值(通常是(shi)500mA和100mA)來支持(chi)USB端口(kou)允許(xu)的(de)(de)(de)最(zui)大(da)電(dian)(dian)(dian)流(liu)(liu)或必(bi)要時的(de)(de)(de)最(zui)小電(dian)(dian)(dian)流(liu)(liu)以確(que)保端口(kou)的(de)(de)(de)完(wan)整性(xing)。通常這要求接口(kou)邏輯嵌入在(zai)充(chong)(chong)電(dian)(dian)(dian)器芯片中，以便系統(tong)微控制(zhi)器能夠連(lian)續讀取(qu)USB端口(kou)的(de)(de)(de)狀態，并指示(shi)充(chong)(chong)電(dian)(dian)(dian)器從一(yi)個充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)切(qie)換到另一(yi)個充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)。

　　最近，有些充(chong)電(dian)器芯(xin)片(pian)制造商已經開發出能夠(gou)自動(dong)檢測USB端(duan)口的(de)可用(yong)功(gong)率、并據此調整充(chong)電(dian)電(dian)流(liu)來(lai)最大(da)化充(chong)電(dian)效率的(de)芯(xin)片(pian)。另外(wai)，許多充(chong)電(dian)器芯(xin)片(pian)不需要用(yong)戶(hu)干涉(she)，就能夠(gou)自動(dong)檢測電(dian)源類(lei)型并調整它們(men)的(de)充(chong)電(dian)過程(cheng)。

　　當凌力(li)爾(er)特公司的LTC4075充電(dian)(dian)器芯(xin)片檢測到輸入端電(dian)(dian)源(yuan)時，它能自動選擇合適(shi)的電(dian)(dian)源(yuan)進行充電(dian)(dian)，同時不需要外接MOSFET、檢測電(dian)(dian)阻或阻流二極管。

　　Microchip Technology公司提供的(de)MCP73837也(ye)能(neng)提供類(lei)似自動的(de)電(dian)源選擇功能(neng)。

　　采用雙節電池

　　隨著便(bian)攜(xie)式(shi)(shi)(shi)系(xi)統(tong)(tong)(tong)設計(ji)復雜性的(de)提高(gao)，它們(men)使用(yong)的(de)子系(xi)統(tong)(tong)(tong)、顯示器(qi)(qi)(qi)(qi)和處理器(qi)(qi)(qi)(qi)的(de)數量與類型(xing)也越來(lai)越多(duo)，單節(jie)鋰(li)離(li)子電(dian)池已經無法滿足系(xi)統(tong)(tong)(tong)需要。因此(ci)，一些便(bian)攜(xie)式(shi)(shi)(shi)媒(mei)體播(bo)放器(qi)(qi)(qi)(qi)、高(gao)性能SLR型(xing)數碼相機和GPS導航(hang)系(xi)統(tong)(tong)(tong)都開始采用(yong)串(chuan)聯的(de)兩節(jie)鋰(li)離(li)子電(dian)池供電(dian)。這(zhe)(zhe)些便(bian)攜(xie)式(shi)(shi)(shi)產(chan)品一般(ban)要求(qiu)輸入在8.4V和8.8V之間進行充電(dian)。設計(ji)師以前都是使用(yong)分立器(qi)(qi)(qi)(qi)件(jian)實現這(zhe)(zhe)種設計(ji)，但支持這(zhe)(zhe)個要求(qiu)的(de)新一代充電(dian)器(qi)(qi)(qi)(qi)芯片(pian)已經開始上市。

　　具有代(dai)表(biao)性(xing)的(de)例子是AT3663，這是Advanced Analogic Technologies公司(AnalogicTech)提供的(de)1A線性(xing)電(dian)(dian)池充電(dian)(dian)器系列芯片的(de)第一個產品，可以(yi)用來給最多兩節串(chuan)聯(lian)的(de)鋰離子電(dian)(dian)池充電(dian)(dian)。AT3663采(cai)用該制(zhi)造商(shang)的(de)專有模塊化(hua)BCD工藝(yi)技術制(zhi)造。這種(zhong)工藝(yi)集成了(le)完全(quan)隔離的(de)CMOS和高速互補雙(shuang)極晶體管(guan)以(yi)及30V DMOS功率器件，沒有采(cai)用復雜而且昂貴的(de)外延(yan)附生(sheng)或(huo)高溫擴散技術。

　　上述新工藝允(yun)許AAT3663支(zhi)持(chi)從4V到13.2V的(de)(de)輸入電壓，因(yin)此設計師可以自由(you)使用較(jiao)低成本的(de)(de)非穩壓適配器(qi)。