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(ji)還需要(yao)哪些(xie)特性來(lai)確(que)保對電(dian)(dian)池進行安(an)全及(ji)精確(que)的充(chong)電(dian)(dian)。

　　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(ting)(ting)止充電(dian)周期，只有當接(jie)合部溫度下降后才(cai)恢復(fu)(fu)工(gong)作(zuo)。如果(guo)這種(zhong)高溫持續存在，那么 充電(dian)器“停(ting)(ting)止和開(kai)始”的反復(fu)(fu)循環也(ye)將繼續發生，從而延長充電(dian)時(shi)間(jian)(jian)。為減(jian)少這些風險，用(yong)戶只能選擇減(jian)小充電(dian)電(dian)流(liu)來延長充電(dian)時(shi)間(jian)(jian)或增(zeng)(zeng)大板(ban)面積(ji)來散熱。因此，由于增(zeng)(zeng)加(jia)了PCB散熱面積(ji)及熱保(bao)護(hu)材料，整個系統(tong)成本也(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，它不必為擔(dan)心(xin)散熱(re)而(er)犧牲PCB面(mian)積，并采用一(yi)種(zhong)(zhong)小型的(de)(de)熱(re)增強封(feng)裝，允許它監(jian)視自己的(de)(de)接合部溫(wen)(wen)度(du)以防(fang)止過(guo)熱(re)。如果達到(dao)預設的(de)(de)溫(wen)(wen)度(du)閾值，充(chong)(chong)電(dian)(dian)(dian)(dian)器能自動減少(shao)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)以限制功(gong)耗，從而(er)使(shi)芯片溫(wen)(wen)度(du)保持(chi)在安全水(shui)平(ping)。第二種(zhong)(zhong)解決方案(an)是使(shi)用一(yi)種(zhong)(zhong)即(ji)使(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)很高(gao)時(shi)也幾乎(hu)不發(fa)熱(re)的(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)器。這要求使(shi)用脈沖充(chong)(chong)電(dian)(dian)(dian)(dian)器，它是一(yi)種(zhong)(zhong)完(wan)全不同于線性(xing)充(chong)(chong)電(dian)(dian)(dian)(dian)器的(de)(de)技術。脈沖充(chong)(chong)電(dian)(dian)(dian)(dian)器依(yi)靠經過(guo)良好調節且電(dian)(dian)(dian)(dian)流(liu)(liu)受限的(de)(de)墻上適(shi)配器來充(chong)(chong)電(dian)(dian)(dian)(dian)。

　　方案一(yi) ： LTC4059A線性(xing)(xing)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器　　LTC4059A是一(yi)款用(yong)(yong)于單(dan)節鋰(li)離(li)子電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池的(de)(de)線性(xing)(xing)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器，它(ta)無(wu)需(xu)使用(yong)(yong)三個(ge)分立功率(lv)器件，可(ke)快速(su)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)而不用(yong)(yong)擔(dan)心系統過熱。監視器負責報(bao)告充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流值，并指示(shi)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器是何時與輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源連接(jie)的(de)(de)。它(ta)采用(yong)(yong)盡可(ke)能小(xiao)的(de)(de)封(feng)裝但沒有犧(xi)牲散熱性(xing)(xing)能。整個(ge)方案僅需(xu)兩個(ge)分立器件(輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容器和一(yi)個(ge)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流編程電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻)，占位面積為2.5mm×2.7mm。 LTC4059A采用(yong)(yong)2mm×2mm DFN封(feng)裝，占位面積只有SOT-23封(feng)裝的(de)(de)一(yi)半(ban)，并能提(ti)供(gong)大約60℃/W的(de)(de)低熱阻，以提(ti)高(gao)散熱效(xiao)率(lv)。通過適當的(de)(de)PCB布局及散熱設(she)計，LTC4059A可(ke)以在輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓為5V的(de)(de)情況下(xia)(xia)以最高(gao)900mA的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流對(dui)單(dan)節鋰(li)離(li)子電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池安全(quan)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。此(ci)外，設(she)計時無(wu)需(xu)考慮最壞(huai)情況下(xia)(xia)的(de)(de)功耗，因為LTC4059A采用(yong)(yong)了專利的(de)(de)熱管理技術，可(ke)以在高(gao)功率(lv)條件(如(ru)環境溫(wen)度過高(gao))下(xia)(xia)自動減小(xiao)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(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)(de)面積 ，且高度低于1.7mm。通過(guo)將功(gong)耗減至最低水平，LTC4052可放寬終端設(she)備對熱(re)(re)(re)設(she)計的(de)(de)要(yao)求(qiu)，允許采(cai)用更小(xiao)的(de)(de)封(feng)裝、更小(xiao)的(de)(de)散熱(re)(re)(re)氣流以及(ji)更小(xiao)的(de)(de)PCB面積，而(er)且能消除(chu)熱(re)(re)(re)點，從而(er)無(wu)需(xu)使用散熱(re)(re)(re)片(pian)或風扇。

　　LTC4052需(xu)要一(yi)個電(dian)流受(shou)限的(de)墻上適配(pei)器，以(yi)控(kong)制充(chong)電(dian)電(dian)流的(de)大小(xiao)。它還需(xu)配(pei)備(bei)過流保(bao)護(hu)電(dian)路(lu)，以(yi)便在意外使(shi)用較(jiao)高(gao)電(dian)流或(huo)(huo)墻上適配(pei)器發生(sheng)故障時(shi)能提供(gong)保(bao)護(hu)。LTC4052是一(yi)款(kuan)全集成的(de)脈沖充(chong)電(dian)器，無需(xu)使(shi)用外部MOSFET或(huo)(huo)阻流二極管 (見圖)。這(zhe)款(kuan)獨立的(de)充(chong)電(dian)器IC具(ju)有C/10檢(jian)測(ce)(ce)、充(chong)電(dian)狀(zhuang)態(tai)指示、充(chong)電(dian)結束定時(shi)器、墻上適配(pei)器檢(jian)測(ce)(ce)及過流保(bao)護(hu)等(deng)功(gong)能。LTC4052的(de)輸入電(dian)源可以(yi)是4.5V到12V，并具(ju)有1%的(de) 飄移電(dian)壓精度。