當今許多靠鋰離子電池供電的手持設備都內建有一個電池充電器，目前通(tong)常使用(yong)一(yi)種線性充電(dian)器(qi)給這種電(dian)池充電(dian)，但這種充電(dian)器(qi)盡管操作(zuo)更簡便和成本更低，但它(ta)(ta)有一(yi)個主要缺點：能耗太高。當輸入(ru)電(dian)壓(ya)為高和電(dian)池電(dian)壓(ya)為低(已(yi)放電(dian)電(dian)池)時，線性充電(dian)器(qi)產生(sheng)的熱量足以損(sun)壞(huai)自(zi)身或其它(ta)(ta)鄰近元件。在(zai)本文(wen)中，凌特技(ji)術公(gong)司提出(chu)了一(yi)種替代方(fang)案，它(ta)(ta)可解決所有的過熱問題而(er)且(qie)充電(dian)快速(su)。

　　當今(jin)許多靠(kao)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)供電(dian)(dian)(dian)(dian)(dian)(dian)的手(shou)持設備都內建有一(yi)(yi)個(ge)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)。這些電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)通(tong)(tong)常都為鋰離子電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)，并且(qie)其(qi)功率密度可在范圍(wei)400mA小時(shi)(shi)到1.5A小時(shi)(shi)變化。你可以(yi)使用一(yi)(yi)種(zhong)線性充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)給這種(zhong)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，而且(qie)這種(zhong)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)通(tong)(tong)常比基(ji)于(yu)轉換器(qi)(qi)的方(fang)案(an)在外形上明顯更(geng)(geng)小，操作(zuo)更(geng)(geng)簡便，成(cheng)本(ben)更(geng)(geng)低(di)(di)，但它有一(yi)(yi)個(ge)主要(yao)缺點(dian)：能耗(hao)太(tai)高(gao)。當輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)為高(gao)和電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)為低(di)(di)(已放電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi))時(shi)(shi)，線性充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)產生的熱量足以(yi)損壞自身或其(qi)它鄰近元件。典型地，這種(zhong)狀態(即(ji)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)隨充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的進行而升高(gao))只是(shi)暫時(shi)(shi)現象，但正是(shi)這些最糟(zao)糕的狀態需要(yao)設計師(shi)在決定充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流與IC溫度的最大(da)容許值時(shi)(shi)必須充(chong)分(fen)地加以(yi)考慮。當然(ran)，一(yi)(yi)種(zhong)解決這種(zhong)過熱問(wen)(wen)題(ti)(ti)的簡單(dan)方(fang)法是(shi)降低(di)(di)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過程中整個(ge)恒流段的充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流，但這種(zhong)方(fang)法伴隨的問(wen)(wen)題(ti)(ti)是(shi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)間的相應延長。

　　不過，凌特技術公司現在提出了一種替代方案，即LTC1733鋰離子單電池線性充電器，它解決了所有的過熱問題且充電快速。這種新穎的IC采用內部反饋來調節充電電流和限制裸片溫度。這意味著更快的充電時間，因為設計師可以通過編程設定一個很高充電電流，而且不會冒任何損壞IC或任何其它元件的風險。這一性能直接帶來的另一好處是毋需設計過熱保護電路。為了進一步改進熱傳遞性，LTC1733采用了熱增強型10針MSOP封裝。該IC只需要3個外部元件便可提供一個完整的鋰離子充電器解決方案。

　　一個(ge)內部功(gong)率MOSFET允(yun)許編程設定(ding)的(de)最(zui)大充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流可(ke)達(da)1.5A，精度(du)為(wei)7%，以(yi)(yi)(yi)(yi)確保(bao)(bao)(bao)(bao)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)快速和完全(quan)。這種內部MOSFET還可(ke)省掉一個(ge)外部電(dian)(dian)(dian)(dian)(dian)流敏感電(dian)(dian)(dian)(dian)(dian)阻或(huo)(huo)(huo)遏流二極管，最(zui)終的(de)無(wu)負載(zai)電(dian)(dian)(dian)(dian)(dian)壓是(shi)引腳可(ke)選的(de)，或(huo)(huo)(huo)為(wei)4.1V或(huo)(huo)(huo)為(wei) 4.2V，精度(du)是(shi)1%，這可(ke)防止過充(chong)(chong)(chong)(chong)帶來的(de)危險(xian)或(huo)(huo)(huo)欠充(chong)(chong)(chong)(chong)造成的(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)容量(liang)不足。遵從(cong)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)制造商的(de)使用(yong)要(yao)求，LTC1733包含了一個(ge)可(ke)編程充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)終止定(ding)時(shi)器和熱敏電(dian)(dian)(dian)(dian)(dian)阻輸(shu)入(ru)，以(yi)(yi)(yi)(yi)保(bao)(bao)(bao)(bao)證充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)全(quan)過程的(de)溫度(du)符合要(yao)求。狀(zhuang)(zhuang)態輸(shu)出(chu)包括：用(yong)以(yi)(yi)(yi)(yi)指示充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)后(hou)期狀(zhuang)(zhuang)態的(de)C/10充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)檢測(ce)、決(jue)定(ding)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)是(shi)否(fou)可(ke)以(yi)(yi)(yi)(yi)進(jin)行下去的(de)壁式電(dian)(dian)(dian)(dian)(dian)源(yuan)適配器狀(zhuang)(zhuang)態檢測(ce)、充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流監測(ce)、以(yi)(yi)(yi)(yi)及用(yong)以(yi)(yi)(yi)(yi)識別(bie)壞電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)錯誤檢測(ce)。低電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)調理電(dian)(dian)(dian)(dian)(dian)路(滴充(chong)(chong)(chong)(chong))可(ke)安全(quan)地為(wei)過放電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，并自(zi)動續充(chong)(chong)(chong)(chong)以(yi)(yi)(yi)(yi)確保(bao)(bao)(bao)(bao)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)總能充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)完全(quan)。當沒有壁式電(dian)(dian)(dian)(dian)(dian)源(yuan)適配器或(huo)(huo)(huo)該部件(jian)關閉的(de)時(shi)候，為(wei)保(bao)(bao)(bao)(bao)持電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)能量(liang)， LTC1733的(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)漏電(dian)(dian)(dian)(dian)(dian)流降(jiang)到5(A以(yi)(yi)(yi)(yi)下。

　　給電池充電
　　給(gei)單(dan)電(dian)(dian)池(chi)鋰(li)離子(zi)電(dian)(dian)池(chi)系統充電(dian)(dian)時(shi)，用戶須在VCC腳處施加(jia)至少4.5V的輸入電(dian)(dian)壓。ACPR腳隨后降為(wei)(wei)低電(dian)(dian)平(pull low)，指(zhi)示(shi)輸入電(dian)(dian)壓條件已(yi)滿足(見圖2)。此外，必須用一個1%的電(dian)(dian)阻器把PROG與GND相連，使額定充電(dian)(dian)電(dian)(dian)流設定為(wei)(wei)100V/RPROG。而后CHPG腳為(wei)(wei)低電(dian)(dian)平，指(zhi)示(shi)充電(dian)(dian)循環開(kai)始。TIMER和GND之間(jian)用電(dian)(dian)容器連接(jie)，充電(dian)(dian)終止時(shi)間(jian)設定為(wei)(wei)3小(xiao)時(shi)/100nF。

　　如果在充(chong)(chong)(chong)電(dian)(dian)(dian)循(xun)環(huan)開始(shi)時(shi)(shi)BAT腳(jiao)的(de)(de)電(dian)(dian)(dian)壓低于2.48V，那(nei)么，充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)將(jiang)(jiang)為(wei)設定值(zhi)的(de)(de)1/10，以使電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓足(zu)夠高，安全實現全充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(見圖3)。如果電(dian)(dian)(dian)池(chi)損壞(huai)，且在1/4的(de)(de)設定終(zhong)止時(shi)(shi)間內電(dian)(dian)(dian)壓都升不(bu)到2.48V以上，則充(chong)(chong)(chong)電(dian)(dian)(dian)循(xun)環(huan)終(zhong)止，且FAULT狀(zhuang)態輸出將(jiang)(jiang)鎖存為(wei)低電(dian)(dian)(dian)平，指示(shi)電(dian)(dian)(dian)池(chi)已壞(huai)。ACPR、CHRG和FAULT三(san)個(ge)狀(zhuang)態輸出腳(jiao)全都產生(sheng)足(zu)夠的(de)(de)電(dian)(dian)(dian)流(liu)(liu)衰弱量(liang)，使LED亮燈。一(yi)旦(dan)電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓升到2.48V以上(充(chong)(chong)(chong)電(dian)(dian)(dian)循(xun)環(huan)開始(shi)后不(bu)久會明顯表(biao)現出來)，LTC1733將(jiang)(jiang)為(wei)電(dian)(dian)(dian)池(chi)提供由RPROG設定的(de)(de)恒(heng)定電(dian)(dian)(dian)流(liu)(liu)。LTC1733將(jiang)(jiang)一(yi)直(zhi)(zhi)保持恒(heng)流(liu)(liu)模式，直(zhi)(zhi)到BAT腳(jiao)的(de)(de)電(dian)(dian)(dian)壓接(jie)近所選擇的(de)(de)最終(zhong)浮置電(dian)(dian)(dian)壓(SEL=0V時(shi)(shi)為(wei) 4.1V ，SEL=VCC時(shi)(shi)為(wei)4.2V)為(wei)止。此(ci)后，器件進入恒(heng)壓模式。

　　在恒壓模式(shi)下(xia)，LTC1733將開始降(jiang)(jiang)低充電(dian)電(dian)流(liu)(liu)(liu)(liu)以保持BAT腳(jiao)的(de)恒壓而非恒流(liu)(liu)(liu)(liu)輸出。當電(dian)流(liu)(liu)(liu)(liu)降(jiang)(jiang)至最(zui)大設定充電(dian)電(dian)流(liu)(liu)(liu)(liu)的(de)10%時(shi)，內部比(bi)較(jiao)器會斷開CHRG腳(jiao)，并將一(yi)弱電(dian)流(liu)(liu)(liu)(liu)源(約25(A)接地，以顯(xian)示接近充電(dian)結束(C/10)狀態(tai)。

　　與電流達到C/10時便結束充電過程的電池充電器不同，LTC1733在(zai)到(dao)達(da)C/10點(dian)后，只要終(zhong)止定(ding)時(shi)(shi)(shi)器時(shi)(shi)(shi)間不到(dao)，會繼(ji)續給電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)，以保證電(dian)(dian)(dian)池(chi)完全充(chong)(chong)滿。在(zai)C/10處(chu)終(zhong)止充(chong)(chong)電(dian)(dian)(dian)過程使電(dian)(dian)(dian)池(chi)只能充(chong)(chong)到(dao)其(qi)容量(liang)的(de)90%到(dao)95%，而在(zai)C/10后繼(ji)續充(chong)(chong)并按(an)時(shi)(shi)(shi)間要求結(jie)束可使電(dian)(dian)(dian)池(chi)的(de)容量(liang)充(chong)(chong)到(dao)100%。一(yi)旦充(chong)(chong)電(dian)(dian)(dian)結(jie)束，CHRG腳便呈現高阻抗狀態。

    電池的再充電
    假(jia)定在(zai)第一次充(chong)電(dian)(dian)時，電(dian)(dian)池(chi)(chi)電(dian)(dian)壓(ya)已充(chong)到了3.95V(SEL = 0V時) 或(huo)(huo)4.05V (SEL = VCC時)以(yi)(yi)上，那么LTC1733可對電(dian)(dian)池(chi)(chi)進(jin)行再(zai)(zai)充(chong)電(dian)(dian)。一旦超出這些閾值，如果電(dian)(dian)池(chi)(chi)電(dian)(dian)壓(ya)因電(dian)(dian)池(chi)(chi)負載的(de)(de)存在(zai)或(huo)(huo)電(dian)(dian)池(chi)(chi)的(de)(de)自放電(dian)(dian)電(dian)(dian)流而掉到3.9V (SEL = 0V)或(huo)(huo)4.0V (SEL = VCC)以(yi)(yi)下(xia)時，則新一輪的(de)(de)充(chong)電(dian)(dian)循(xun)(xun)環(huan)開始了。再(zai)(zai)充(chong)電(dian)(dian)電(dian)(dian)路集結BAT腳電(dian)(dian)壓(ya)數毫秒，以(yi)(yi)防止(zhi)充(chong)電(dian)(dian)循(xun)(xun)環(huan)重啟(qi)造(zao)成的(de)(de)瞬態(tai)沖擊(ji)。

    熱調節
　　LTC1733的(de)另(ling)一(yi)個特性(xing)是具有(you)內部熱調節回路。如果高(gao)功率操作或高(gao)的(de)環(huan)境溫度導致LTC1733的(de)溫度接近105(C，那么充電(dian)電(dian)流(liu)會自動降低以將(jiang)溫度保持在105(C左右 (板溫度通(tong)常(chang)低于85(C)，這便是所謂的(de)恒溫模式。這一(yi)特性(xing)允(yun)許用戶基于具體的(de)工作條件設定(ding)充電(dian)電(dian)流(liu)，并去掉許多線性(xing)應用必需的(de)復雜(za)過熱保護設計(ji)。

　　LTC1733會(hui)自動(dong)監視最糟狀態，這一(yi)特性(xing)除(chu)可(ke)保護LTC1733外，還能去除(chu)板上的“熱(re)點(dian)”區，從而保護周邊(bian)元件。其(qi)它的電(dian)池(chi)充(chong)電(dian)器，其(qi)熱(re)關閉(bi)特性(xing)只是簡單(dan)地在極高溫(wen)度(du)(du)下(xia)(一(yi)般是150(C)關閉(bi)充(chong)電(dian)器而已。這種(zhong)基于溫(wen)度(du)(du)的關閉(bi)特性(xing)允許電(dian)池(chi)充(chong)電(dian)器和周邊(bian)PCB板溫(wen)度(du)(du)升至(zhi)非常高，盡管具備關閉(bi)“保護”功能，但必須(xu)對(dui)應用(yong)進行仔細設計(ji)以避免到達熱(re)關閉(bi)溫(wen)度(du)(du)。LTC1733通過自動(dong)均衡充(chong)電(dian)電(dian)流、散熱(re)和工作溫(wen)度(du)(du)，可(ke)使(shi)設計(ji)得到簡化。

　　為進一步改進LTC1733的(de)熱(re)調節性能，它采用(yong)了熱(re)增強(qiang)型MSOP封(feng)裝。其占用(yong)板面積可做(zuo)到小于(yu)72 mm2，室溫功耗2W。這相當于(yu)用(yong)5V輸入(ru)電(dian)源實(shi)現最(zui)大(da)充電(dian)電(dian)流1.5A。這里假定鋰(li)離子電(dian)池在充電(dian)大(da)部分時間里處于(yu)(3.7V狀態。實(shi)際上(shang)，由于(yu)典(dian)型的(de)鋰(li)離子電(dian)池在充電(dian)開(kai)始幾分鐘內便升到3.8V以(yi)上(shang)，因此這一假定有(you)些保守。LTC1733的(de)這一獨特熱(re)特性和7%的(de)設定充電(dian)電(dian)流精度(du)，使單電(dian)池鋰(li)離子電(dian)池系(xi)統(tong)的(de)充電(dian)過(guo)程非常迅速(su)和精確(que)。

　　PROG電流監控器
　　在恒流(liu)模式下，PROG腳(jiao)的電壓總為(wei)1.5V，指示設定的充電電流(liu)從BAT腳(jiao)流(liu)出。在恒溫或恒壓模式下，BAT腳(jiao)的電流(liu)有(you)所下降(jiang)。PROG腳(jiao)與三個開漏狀態輸出(ACPR、CHRG和 FAULT)時刻通告用戶LTC1733到底在做什么。

　　NTC熱敏電阻
　　除了可編程定(ding)(ding)時器和低的(de)電(dian)池(chi)(chi)充電(dian)限定(ding)(ding)條件外(wai)，LTC1733在推薦給電(dian)池(chi)(chi)制(zhi)造商的(de)安全性特(te)性列表中(zhong)還增加了充電(dian)時的(de)溫度限定(ding)(ding)。電(dian)池(chi)(chi)溫度通過(guo)緊貼電(dian)池(chi)(chi)組放置(zhi)一只負溫度系數(shu)(NTC)熱敏電(dian)阻來(lai)測定(ding)(ding)。借(jie)助IC中(zhong)的(de)內(nei)部(bu)溫度限制(zhi)電(dian)路，LTC1733在電(dian)池(chi)(chi)溫度降到0(C以(yi)下或(huo)升到50(C以(yi)上時，可臨(lin)時停住內(nei)部(bu)定(ding)(ding)時器并停止(zhi)充電(dian)。實(shi)施這一功能，選(xuan)用RHOT的(de)電(dian)阻值(zhi)應與(yu)50(C下所用熱敏電(dian)阻的(de)阻值(zhi)相同。這樣將可以(yi)確保內(nei)部(bu)比較器的(de)1/2VCC摔點(trip point)與(yu)NTC的(de)50(C溫度相對應。

　　還有，選定的NTC熱敏電阻在0(C時的阻值應盡量接近50(C時阻值的7倍。7：1的冷熱NTC比率可確保內部比較器7/8VCC的摔點與NTC 0(C的溫度相對應。每個熱和冷比較器都有約2(C的滯后以防摔點的振蕩。另外，NTC可以不使用任何外部元件，只簡單地通過將NTC腳接地就可使其功能失效。
 
　　結論
　　LTC1733是一種全功能的獨立鋰離子電池充電器。其結構極為簡單，只需要三個外部元件，就可安全精確地將高容量電池快充至1.5A的充電電流。在體現安全性及狀態特性方面，可加上一只NTC熱敏電阻和幾個LED。目前許多用鋰離子電池作供電電源的設備可采用這種類型的充電器，如數字靜態照相機(DSC)、個人數字助理(PDA)、蜂窩電話、MP3播放機以及GPS系統等。
 
　　值得注意的是，對上述諸多產品中有許多產品，有一種需求越來越強烈。就是通過ＵＳＢ接口插入一個主設備時，電池正在充電。盡管LTC1733可用于這類充電應用，但USB端口的可獲電流量有限，或500mA 或 100mA，依連接外設的數量而定。而在這些應用中LTC1733存在的一個缺陷是關閉模式下的靜態電流為0.9mA。這是一個難點，因為USB規范定義了一種暫停(SUSPEND)模式，即在USB+5V的情況下，漏電電流必須低于500(A。不過，凌特技術公司還有LTC4053，一種與USB兼容的鋰離子電池充電器。它在關閉模式下源電流僅為25(A。所以，當外設在USB請求暫停模式時，將中LTC4053，以滿足所要求的漏電電流限制。
 
    凌特公司（Linear Technology）推出獨立的開關模式鋰離子電池充電器 LTC4002，工作電源電壓可高達 24V，從而不需要 9V 和更高電壓墻上適配器所需的輸入瞬變保護。另外，器件的 4.7V 低輸入電源以及低壓差工作特性保證了 4.2V 鋰離子電池可從 5V 墻上適配器持續充電。為了實現安全自主的充電控制，LTC4002 還包括自動關機、電池預查驗、電池溫度檢測、充電結束指示以及一個充電 3 小時終止定時器等特性。
 
　　與遲滯拓樸結構充電器相比，LTC4002 恒定的 500kHz 工作頻率和電流模式結構允許使用更小的電感器和電容器。由于 100mV 的低檢測電壓，所以很容易達到超過86%。這種獨立的充電器有兩種封裝，3mm×3mm DFN 和 8 引線 SO。LTC4002 可應用于手持式儀表和通信裝置、充電座、便攜式計算機以及電池備份系統。
 
　　LTC4002 是一種高效率電流模式 PWM 控制器，開關頻率為 500kHz。它驅動一個外部 P 溝道 MOSFET，以最高 87% 的效率提供高達 2A 的充電電流。這種集成電路的恒定開關頻率將噪聲和濾波需求減至最低。配合使用各類輸出電容器（包括低 ESR 陶瓷電容器），LTC4002 都是穩定的。一個內部比較器檢測充電結束電流，而集成的定時器設定總充電時間，并在三小時后終止充電。LTC4002 自動進入休眠模式，使電池耗用電流降至 10uA。而且，當電池電壓降至 4.05V 以下時，這種集成電路還能自動開始充電
。
　　LTC4002 的工作溫度定在 －40°C 到 85°C。以 1000 片為單位批量購買，每片起價為 1.95美元。
 
　　LTC4002 性能概要：