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，以及還(huan)需要哪些(xie)特(te)性來確保(bao)對電池進行(xing)安全及精確的充電。

　　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(zhi)充(chong)電(dian)周期(qi)，只有當接合部溫度下降后才恢(hui)復工作。如(ru)果這(zhe)(zhe)種(zhong)高溫持續存在，那么 充(chong)電(dian)器“停止(zhi)和開始”的反復循環也(ye)(ye)將繼續發生，從(cong)而延(yan)長充(chong)電(dian)時(shi)間。為減少這(zhe)(zhe)些風(feng)險，用戶只能(neng)選擇減小(xiao)充(chong)電(dian)電(dian)流來(lai)延(yan)長充(chong)電(dian)時(shi)間或(huo)增大板面積來(lai)散熱。因(yin)此，由于增加了PCB散熱面積及熱保護材料，整個系(xi)統成本也(ye)(ye)將上(shang)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(ta)(ta)不必(bi)為擔心散熱(re)而犧牲(sheng)PCB面(mian)積，并(bing)采用(yong)一種(zhong)小型的(de)熱(re)增強封裝(zhuang)，允許它(ta)(ta)監視(shi)自(zi)己的(de)接合部溫(wen)度以(yi)(yi)防止過熱(re)。如果達到(dao)預設的(de)溫(wen)度閾值，充(chong)(chong)(chong)電(dian)(dian)器能(neng)自(zi)動減少(shao)充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流以(yi)(yi)限制功耗，從而使芯片溫(wen)度保持在安全水平(ping)。第二(er)種(zhong)解決方案是(shi)使用(yong)一種(zhong)即使充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流很高(gao)時也幾乎不發熱(re)的(de)充(chong)(chong)(chong)電(dian)(dian)器。這要求使用(yong)脈沖充(chong)(chong)(chong)電(dian)(dian)器，它(ta)(ta)是(shi)一種(zhong)完(wan)全不同于線性(xing)充(chong)(chong)(chong)電(dian)(dian)器的(de)技術。脈沖充(chong)(chong)(chong)電(dian)(dian)器依靠經過良(liang)好調節且電(dian)(dian)流受限的(de)墻上適配器來充(chong)(chong)(chong)電(dian)(dian)。

　　方案一(yi) ： LTC4059A線性電(dian)(dian)池充(chong)(chong)(chong)(chong)電(dian)(dian)器(qi)(qi)　　LTC4059A是(shi)一(yi)款用(yong)(yong)于單節鋰(li)(li)離(li)子(zi)電(dian)(dian)池的(de)線性充(chong)(chong)(chong)(chong)電(dian)(dian)器(qi)(qi)，它無需使用(yong)(yong)三個分(fen)立(li)功率器(qi)(qi)件(jian)，可快速(su)充(chong)(chong)(chong)(chong)電(dian)(dian)而不用(yong)(yong)擔心系統過熱。監視(shi)器(qi)(qi)負責報告充(chong)(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流值，并(bing)指示充(chong)(chong)(chong)(chong)電(dian)(dian)器(qi)(qi)是(shi)何(he)時(shi)(shi)與輸(shu)入電(dian)(dian)源連接的(de)。它采(cai)用(yong)(yong)盡可能小的(de)封裝但沒有(you)犧牲(sheng)散熱性能。整個方案僅需兩個分(fen)立(li)器(qi)(qi)件(jian)(輸(shu)入電(dian)(dian)容器(qi)(qi)和一(yi)個充(chong)(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流編程電(dian)(dian)阻)，占位(wei)面積為(wei)2.5mm×2.7mm。 LTC4059A采(cai)用(yong)(yong)2mm×2mm DFN封裝，占位(wei)面積只(zhi)有(you)SOT-23封裝的(de)一(yi)半，并(bing)能提供大約60℃/W的(de)低熱阻，以(yi)提高(gao)散熱效率。通過適當的(de)PCB布局及(ji)散熱設(she)計，LTC4059A可以(yi)在輸(shu)入電(dian)(dian)壓為(wei)5V的(de)情況(kuang)下(xia)以(yi)最高(gao)900mA的(de)電(dian)(dian)流對單節鋰(li)(li)離(li)子(zi)電(dian)(dian)池安全(quan)充(chong)(chong)(chong)(chong)電(dian)(dian)。此(ci)外，設(she)計時(shi)(shi)無需考慮最壞情況(kuang)下(xia)的(de)功耗(hao)，因(yin)為(wei)LTC4059A采(cai)用(yong)(yong)了專利的(de)熱管理技術(shu)，可以(yi)在高(gao)功率條件(jian)(如環境溫度過高(gao))下(xia)自(zi)動(dong)減小充(chong)(chong)(chong)(chong)電(dian)(dian)電(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(jin)占70mm2 的(de)面(mian)積 ，且(qie)高度低(di)于(yu)1.7mm。通過(guo)將功耗減至最低(di)水平(ping)，LTC4052可放寬終端設備對熱(re)(re)(re)設計的(de)要求，允許采用更小(xiao)(xiao)的(de)封裝、更小(xiao)(xiao)的(de)散熱(re)(re)(re)氣流以及更小(xiao)(xiao)的(de)PCB面(mian)積，而且(qie)能消除(chu)熱(re)(re)(re)點(dian)，從(cong)而無需(xu)使(shi)用散熱(re)(re)(re)片(pian)或風扇。

　　LTC4052需要一個電(dian)(dian)(dian)(dian)(dian)(dian)流受限(xian)的(de)墻上適配(pei)器(qi)，以控制(zhi)充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)大小。它(ta)還需配(pei)備(bei)過流保護(hu)電(dian)(dian)(dian)(dian)(dian)(dian)路，以便在意(yi)外使用較高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)流或(huo)墻上適配(pei)器(qi)發生故障(zhang)時能(neng)提供(gong)保護(hu)。LTC4052是(shi)一款全集成(cheng)的(de)脈沖充電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)，無需使用外部MOSFET或(huo)阻(zu)流二極管 (見圖)。這款獨立的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)IC具有C/10檢(jian)測、充電(dian)(dian)(dian)(dian)(dian)(dian)狀態(tai)指示、充電(dian)(dian)(dian)(dian)(dian)(dian)結束定(ding)時器(qi)、墻上適配(pei)器(qi)檢(jian)測及(ji)過流保護(hu)等功(gong)能(neng)。LTC4052的(de)輸入電(dian)(dian)(dian)(dian)(dian)(dian)源可以是(shi)4.5V到12V，并具有1%的(de) 飄移電(dian)(dian)(dian)(dian)(dian)(dian)壓精(jing)度。