所有3G手機都采用鋰離子電池作為主電源。由于散熱及空間的限制，設計師必須仔細考慮選用何種類型的電池充電器，以(yi)及(ji)還需要(yao)哪些(xie)特性(xing)來確保對電池進行(xing)安全及(ji)精(jing)確的(de)充電。

　　線性鋰離子電池充電器的一個明顯趨勢是封裝尺寸繼續減小。但值得關注的是在充電周期(尤其在高電流階段)冷卻IC所需的板空間或通風條件。充電器的功耗會使IC的接合部溫度上升。加上環境溫度，它會達到足夠高的水平，使IC過熱并降低電路可靠性。此外，如果過熱，許多充電器會停止充(chong)電(dian)周期，只(zhi)(zhi)有當接合部(bu)溫度下降后才恢復工作。如果這種高(gao)溫持續(xu)(xu)存在(zai)，那(nei)么 充(chong)電(dian)器(qi)“停止和(he)開始(shi)”的反復循環也將(jiang)繼續(xu)(xu)發生(sheng)，從而(er)延長充(chong)電(dian)時(shi)間(jian)。為減(jian)少這些風險(xian)，用戶只(zhi)(zhi)能選擇(ze)減(jian)小充(chong)電(dian)電(dian)流來(lai)延長充(chong)電(dian)時(shi)間(jian)或增(zeng)大板面積(ji)來(lai)散熱。因(yin)此，由于增(zeng)加了PCB散熱面積(ji)及熱保護(hu)材料，整個(ge)系統成本(ben)也將(jiang)上升。

　　對此問題有兩種解決方案。首先，需要一種智能的線性鋰離子電池充電器，它不必為擔心散熱而犧牲PCB面積，并采(cai)用一種(zhong)(zhong)小(xiao)型的熱增強封(feng)裝，允(yun)許它監視自(zi)己的接合部溫(wen)度(du)以(yi)防(fang)止過(guo)熱。如果達到預設的溫(wen)度(du)閾值，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)能自(zi)動減少充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)以(yi)限制功耗，從而使芯片溫(wen)度(du)保持(chi)在安(an)全水平。第(di)二種(zhong)(zhong)解決方案是(shi)使用一種(zhong)(zhong)即使充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)很高時也幾乎(hu)不發熱的充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)。這要(yao)求使用脈沖(chong)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)，它是(shi)一種(zhong)(zhong)完(wan)全不同于線性充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)的技術。脈沖(chong)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)依靠經過(guo)良好調節且電(dian)(dian)(dian)(dian)流(liu)受(shou)限的墻上適配器(qi)來充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)。

　　方案(an)一(yi)(yi) ： LTC4059A線(xian)性(xing)電(dian)(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)　　LTC4059A是一(yi)(yi)款用于單節鋰離(li)子電(dian)(dian)(dian)(dian)(dian)池的(de)(de)線(xian)性(xing)充電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)，它無(wu)需(xu)使用三(san)個(ge)分立(li)功(gong)率器(qi)(qi)(qi)件(jian)，可(ke)快速充電(dian)(dian)(dian)(dian)(dian)而(er)不用擔心系統過熱(re)(re)。監視器(qi)(qi)(qi)負責報告充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流值，并指示充電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)是何時(shi)與輸(shu)入電(dian)(dian)(dian)(dian)(dian)源連接的(de)(de)。它采(cai)用盡可(ke)能(neng)小(xiao)的(de)(de)封裝但沒有犧牲(sheng)散熱(re)(re)性(xing)能(neng)。整(zheng)個(ge)方案(an)僅需(xu)兩個(ge)分立(li)器(qi)(qi)(qi)件(jian)(輸(shu)入電(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)(qi)和一(yi)(yi)個(ge)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流編程(cheng)電(dian)(dian)(dian)(dian)(dian)阻)，占(zhan)位面積(ji)為2.5mm×2.7mm。 LTC4059A采(cai)用2mm×2mm DFN封裝，占(zhan)位面積(ji)只有SOT-23封裝的(de)(de)一(yi)(yi)半，并能(neng)提(ti)供大(da)約60℃/W的(de)(de)低(di)熱(re)(re)阻，以提(ti)高(gao)散熱(re)(re)效率。通過適(shi)當(dang)的(de)(de)PCB布局及散熱(re)(re)設計，LTC4059A可(ke)以在(zai)(zai)輸(shu)入電(dian)(dian)(dian)(dian)(dian)壓為5V的(de)(de)情(qing)(qing)況下以最高(gao)900mA的(de)(de)電(dian)(dian)(dian)(dian)(dian)流對單節鋰離(li)子電(dian)(dian)(dian)(dian)(dian)池安全充電(dian)(dian)(dian)(dian)(dian)。此外，設計時(shi)無(wu)需(xu)考慮最壞(huai)情(qing)(qing)況下的(de)(de)功(gong)耗，因為LTC4059A采(cai)用了專(zhuan)利的(de)(de)熱(re)(re)管理技術，可(ke)以在(zai)(zai)高(gao)功(gong)率條件(jian)(如環境溫度過高(gao))下自動(dong)減小(xiao)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流。

　　方案二 ：帶過流保護功能的LTC4052脈沖充電器　　LTC4052是一款全集成的脈沖充電器，用于單節4.2V鋰離子/鋰聚合物電池。當輸入電壓為5.25V并以0.8A電流進行快速充電時，LTC4052的功耗大約為280mW，而線性充電器解決方案的功耗則高達1.8W。與采用電感來獲得高效率和低散熱的開關充電器不同，LTC4052采用無電感設計。利用LTC4052設計的700mA至2A鋰離子/鋰聚合物電池充電器電路僅占70mm2 的(de)面積 ，且高度低于1.7mm。通(tong)過將功耗(hao)減(jian)至最低水平，LTC4052可放(fang)寬終(zhong)端設備對(dui)熱(re)設計的(de)要求，允許采用更(geng)小的(de)封裝、更(geng)小的(de)散(san)(san)熱(re)氣流(liu)以(yi)及更(geng)小的(de)PCB面積，而(er)且能消(xiao)除熱(re)點，從而(er)無(wu)需使(shi)用散(san)(san)熱(re)片(pian)或風扇。

　　LTC4052需(xu)要一個電(dian)(dian)流受限的墻上適配器，以控制充(chong)(chong)電(dian)(dian)電(dian)(dian)流的大(da)小。它還(huan)需(xu)配備過流保護電(dian)(dian)路，以便(bian)在意外使(shi)用較高電(dian)(dian)流或墻上適配器發(fa)生故障時能提供保護。LTC4052是一款(kuan)全集(ji)成的脈沖(chong)充(chong)(chong)電(dian)(dian)器，無需(xu)使(shi)用外部(bu)MOSFET或阻流二(er)極管 (見圖)。這款(kuan)獨立(li)的充(chong)(chong)電(dian)(dian)器IC具(ju)有C/10檢(jian)測、充(chong)(chong)電(dian)(dian)狀態指示、充(chong)(chong)電(dian)(dian)結束定時器、墻上適配器檢(jian)測及過流保護等功能。LTC4052的輸(shu)入電(dian)(dian)源可以是4.5V到12V，并具(ju)有1%的 飄移電(dian)(dian)壓精度。