作為控制鋰離子充電狀態的功率器件，電池充電器芯(xin)片(pian)在便(bian)攜式系(xi)統設(she)計(ji)中扮演著重要的(de)(de)角色。然而，設(she)計(ji)師們還(huan)在使(shi)用著從較老并且(qie)相對粗糙和低成本的(de)(de)充電(dian)器(qi)件、到較新的(de)(de)更復雜芯(xin)片(pian)等(deng)各種各樣的(de)(de)器(qi)件，而后者集成了越來越復雜的(de)(de)智能，可以(yi)延長電(dian)池壽命(ming)，保(bao)護被充電(dian)系(xi)統不受(shou)損害。

　　安全第一

　　便攜式系統設(she)計師面(mian)臨的(de)挑戰(zhan)是：如何快速(su)高效(xiao)地對系統進行充(chong)電(dian)(dian)(dian)，同時不(bu)影響用(yong)戶安(an)全或損壞電(dian)(dian)(dian)池(chi)，并且要(yao)占用(yong)最少的(de)電(dian)(dian)(dian)路板面(mian)積。鋰(li)離(li)子充(chong)電(dian)(dian)(dian)器通(tong)常(chang)采用(yong)三種充(chong)電(dian)(dian)(dian)模式來最大化充(chong)電(dian)(dian)(dian)效(xiao)率并確(que)保用(yong)戶安(an)全性。深(shen)度放(fang)電(dian)(dian)(dian)的(de)電(dian)(dian)(dian)池(chi)必須(xu)先用(yong)較小的(de)電(dian)(dian)(dian)流進行逐步(bu)預充(chong)電(dian)(dian)(dian)，將(jiang)電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓慢慢提升到安(an)全閥值之上。

　　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(shuo)，它通常(chang)會測(ce)量被充(chong)(chong)(chong)電(dian)(dian)池(chi)的(de)電(dian)(dian)壓，當電(dian)(dian)池(chi)電(dian)(dian)壓低于(yu)3V時(shi)，它將(jiang)進(jin)入預充(chong)(chong)(chong)或“慢(man)充(chong)(chong)(chong)”模式(shi)。慢(man)充(chong)(chong)(chong)模式(shi)可以在電(dian)(dian)池(chi)內阻很低時(shi)防止(zhi)對電(dian)(dian)池(chi)高速充(chong)(chong)(chong)電(dian)(dian)，從而盡量減(jian)少發熱。一般預充(chong)(chong)(chong)期間的(de)充(chong)(chong)(chong)電(dian)(dian)速率(lv)約是(shi)全速充(chong)(chong)(chong)電(dian)(dian)時(shi)的(de)10%。

　　圖(tu)1：Microchip科(ke)技公(gong)司(si)的MCP73837雙(shuang)輸入鋰離(li)子/聚合物充(chong)電(dian)(dian)器具有電(dian)(dian)源選(xuan)擇功能，可以自動選(xuan)擇從(cong)交流或(huo)USB源進(jin)行充(chong)電(dian)(dian)。

　　一旦(dan)電(dian)池(chi)達(da)到(dao)最小電(dian)壓值(zhi)，充(chong)(chong)電(dian)器就切(qie)換到(dao)恒(heng)(heng)流(liu)或快充(chong)(chong)模(mo)式，此時(shi)將對電(dian)池(chi)全(quan)速充(chong)(chong)電(dian)，直到(dao)電(dian)池(chi)達(da)到(dao)接(jie)近(jin)滿(man)充(chong)(chong)電(dian)壓的第二(er)個閥值(zhi)。隨后充(chong)(chong)電(dian)器將進入恒(heng)(heng)壓模(mo)式，此時(shi)電(dian)池(chi)電(dian)壓保持不變，從(cong)而讓充(chong)(chong)電(dian)電(dian)流(liu)逐漸(jian)停(ting)止。當充(chong)(chong)電(dian)電(dian)流(liu)小于預(yu)設的終止閥值(zhi)時(shi)，恒(heng)(heng)壓充(chong)(chong)電(dian)模(mo)式也就結束了(le)。

　　熱管(guan)理是電(dian)池(chi)(chi)充(chong)(chong)電(dian)器設(she)計(ji)師面(mian)臨的(de)(de)(de)另一大(da)挑戰。每個充(chong)(chong)電(dian)器芯片(pian)都(dou)會(hui)在充(chong)(chong)電(dian)過(guo)程中(zhong)經歷由于散熱引起的(de)(de)(de)電(dian)壓下降。為了避免電(dian)池(chi)(chi)損壞或(huo)(huo)系統(tong)(tong)關(guan)斷(duan)(duan)，大(da)多數充(chong)(chong)電(dian)器都(dou)集(ji)成(cheng)了某種形式的(de)(de)(de)控制機制來(lai)管(guan)理熱量累積(ji)。較老的(de)(de)(de)充(chong)(chong)電(dian)器芯片(pian)常采用(yong)“非彼即此”的(de)(de)(de)方(fang)法來(lai)解決(jue)過(guo)熱或(huo)(huo)過(guo)流問(wen)題――當(dang)熱量達到預設(she)的(de)(de)(de)門限時它們將簡(jian)單地中(zhong)斷(duan)(duan)充(chong)(chong)電(dian)過(guo)程。較新的(de)(de)(de)器件則采用(yong)更(geng)復雜的(de)(de)(de)反饋(kui)技術連(lian)續監視裸片(pian)溫度，并(bing)以(yi)正比于環境溫度變化(hua)的(de)(de)(de)速率動態或(huo)(huo)通過(guo)計(ji)算(suan)調整充(chong)(chong)電(dian)電(dian)流。這(zhe)種內(nei)置智能允許當(dang)前的(de)(de)(de)充(chong)(chong)電(dian)器芯片(pian)逐(zhu)漸減少(shao)充(chong)(chong)電(dian)電(dian)流，直到達到熱平衡，裸片(pian)溫度停止上(shang)升。這(zhe)種技術能讓充(chong)(chong)電(dian)器以(yi)最(zui)大(da)可能的(de)(de)(de)電(dian)流對電(dian)池(chi)(chi)進行連(lian)續充(chong)(chong)電(dian)，同時不(bu)會(hui)導致系統(tong)(tong)關(guan)斷(duan)(duan)，從(cong)而縮(suo)短電(dian)池(chi)(chi)充(chong)(chong)電(dian)時間。

　　MAX8804是美信集成產品(pin)公司(si)去年(nian)7月份推出的充電(dian)器(qi)芯片(pian)，它采(cai)用(yong)了專門的熱調整(zheng)電(dian)路(lu)，可(ke)以在快速充電(dian)階段或系統處于高(gao)溫環境(jing)(jing)中(zhong)(zhong)限制(zhi)(zhi)裸片(pian)的溫度(du)。該充電(dian)器(qi)耐受30V的直流(liu)輸入電(dian)壓(ya)，只占(zhan)用(yong)6平方毫米(mi)的電(dian)路(lu)板面(mian)積。另外，像TI公司(si)提(ti)供(gong)的1A bq24060充電(dian)器(qi)可(ke)提(ti)供(gong)熱過載保(bao)(bao)護功能(neng)，允許器(qi)件(jian)在環境(jing)(jing)溫度(du)很高(gao)的惡劣環境(jing)(jing)中(zhong)(zhong)連(lian)續運(yun)行，例(li)如夏天的汽車(che)或不小心連(lian)接到具(ju)有(you)較高(gao)輸入電(dian)壓(ya)的其它適配器(qi)。目(mu)前大多數較新的器(qi)件(jian)一般還(huan)會增加(jia)過壓(ya)保(bao)(bao)護機制(zhi)(zhi)。

　　多種電壓源

　　有個越來越常(chang)見的(de)要(yao)(yao)求是(shi)從不(bu)同電(dian)(dian)壓源給電(dian)(dian)池充電(dian)(dian)，要(yao)(yao)點(dian)是(shi)在不(bu)使電(dian)(dian)壓源過載的(de)情(qing)況下提(ti)供這(zhe)個功(gong)能。可以通過在輸(shu)入條件改變時動(dong)態調整(zheng)充電(dian)(dian)電(dian)(dian)流實現這(zhe)一(yi)功(gong)能。

　　舉例來(lai)說，移動用戶經常沒有(you)時間去找(zhao)交(jiao)流電(dian)(dian)(dian)(dian)(dian)插座來(lai)給他(ta)們(men)的(de)設備充(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)設備上都有(you)的(de)眾多USB端(duan)口(kou)(kou)來(lai)給他(ta)們(men)的(de)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)，包括其它電(dian)(dian)(dian)(dian)(dian)池(chi)供電(dian)(dian)(dian)(dian)(dian)的(de)設備，如筆記本電(dian)(dian)(dian)(dian)(dian)腦。因此(ci)，目(mu)前市場(chang)上的(de)許(xu)多充(chong)電(dian)(dian)(dian)(dian)(dian)器芯片支持(chi)從交(jiao)流和USB輸入(ru)口(kou)(kou)給單節鋰(li)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)。此(ci)時的(de)挑戰是補償USB端(duan)口(kou)(kou)提供的(de)不斷變(bian)化的(de)功(gong)率電(dian)(dian)(dian)(dian)(dian)平。隨著負載的(de)變(bian)化，系統必須控制恒(heng)定的(de)充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流值以確保USB端(duan)口(kou)(kou)的(de)正常操作(zuo)。

　　一些充(chong)(chong)電(dian)(dian)(dian)器芯(xin)片(pian)利(li)用簡單的(de)雙重方(fang)法(fa)支持USB操作，該方(fang)法(fa)使(shi)用兩個預(yu)設的(de)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)值(zhi)(通常是(shi)500mA和100mA)來支持USB端口允許的(de)最大(da)電(dian)(dian)(dian)流(liu)或必要(yao)時的(de)最小電(dian)(dian)(dian)流(liu)以確保端口的(de)完整性。通常這要(yao)求(qiu)接口邏輯嵌入在充(chong)(chong)電(dian)(dian)(dian)器芯(xin)片(pian)中，以便系統微控(kong)制器能夠連續讀(du)取USB端口的(de)狀態(tai)，并指示充(chong)(chong)電(dian)(dian)(dian)器從一個充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)切換到另一個充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)。

　　最近，有些充(chong)電(dian)器芯片(pian)制造商已經(jing)開(kai)發出能夠自動檢測USB端口的可用功率、并據此調整(zheng)充(chong)電(dian)電(dian)流來最大(da)化充(chong)電(dian)效率的芯片(pian)。另外，許多充(chong)電(dian)器芯片(pian)不需要(yao)用戶干涉(she)，就能夠自動檢測電(dian)源類型并調整(zheng)它們的充(chong)電(dian)過程。

　　當凌(ling)力爾(er)特公司的LTC4075充電(dian)(dian)器(qi)芯(xin)片檢(jian)測到輸入端電(dian)(dian)源時，它能自動選擇(ze)合適的電(dian)(dian)源進行(xing)充電(dian)(dian)，同時不需要(yao)外(wai)接MOSFET、檢(jian)測電(dian)(dian)阻或阻流二極管。

　　Microchip Technology公(gong)司(si)提供的MCP73837也能(neng)提供類似自動的電(dian)源選擇功(gong)能(neng)。

　　采用雙節電池

　　隨(sui)著便攜式(shi)系(xi)統(tong)設計(ji)復雜性(xing)的(de)提高，它(ta)們使用(yong)(yong)的(de)子系(xi)統(tong)、顯示(shi)器和處理器的(de)數量與(yu)類型也越來(lai)越多，單(dan)節(jie)鋰離子電池(chi)已經無法滿足系(xi)統(tong)需(xu)要(yao)(yao)。因此(ci)，一(yi)些便攜式(shi)媒體播放器、高性(xing)能SLR型數碼(ma)相(xiang)機和GPS導航系(xi)統(tong)都開始采用(yong)(yong)串(chuan)聯的(de)兩節(jie)鋰離子電池(chi)供電。這些便攜式(shi)產品(pin)一(yi)般要(yao)(yao)求輸入在(zai)8.4V和8.8V之間進行充電。設計(ji)師以(yi)前都是使用(yong)(yong)分立器件實現這種(zhong)設計(ji)，但支持這個要(yao)(yao)求的(de)新(xin)一(yi)代(dai)充電器芯片已經開始上(shang)市。

　　具有代表性的(de)例(li)子是(shi)AT3663，這是(shi)Advanced Analogic Technologies公(gong)司(AnalogicTech)提(ti)供(gong)的(de)1A線(xian)性電池充電器系列芯片的(de)第一(yi)個產品，可以用來給最多兩節串聯的(de)鋰離子電池充電。AT3663采用該制造(zao)商的(de)專有模塊化BCD工藝(yi)技術(shu)制造(zao)。這種工藝(yi)集成了完全隔離的(de)CMOS和(he)高速互補雙極晶體管以及30V DMOS功(gong)率器件，沒(mei)有采用復雜而且(qie)昂貴的(de)外(wai)延(yan)附生或高溫擴(kuo)散(san)技術(shu)。

　　上(shang)述新工藝允許AAT3663支持從4V到(dao)13.2V的輸入電壓(ya)，因此(ci)設計師可(ke)以(yi)自由使用較低成本的非穩壓(ya)適配器。