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，目前通常(chang)使用一(yi)種(zhong)線性充電(dian)器(qi)(qi)給(gei)這(zhe)(zhe)種(zhong)電(dian)池(chi)充電(dian)，但這(zhe)(zhe)種(zhong)充電(dian)器(qi)(qi)盡管操(cao)作更簡便和成本更低，但它(ta)有一(yi)個主要缺點：能耗太(tai)高(gao)。當輸入電(dian)壓(ya)為高(gao)和電(dian)池(chi)電(dian)壓(ya)為低(已放電(dian)電(dian)池(chi))時，線性充電(dian)器(qi)(qi)產生的熱(re)量足以(yi)損壞自身或其它(ta)鄰近元件。在本文中，凌特技(ji)術公(gong)司提出(chu)了一(yi)種(zhong)替代(dai)方案，它(ta)可解決所有的過熱(re)問題而且(qie)充電(dian)快速。

　　當今許(xu)多靠電(dian)(dian)(dian)(dian)池(chi)(chi)供電(dian)(dian)(dian)(dian)的手持設備都內建有(you)一(yi)(yi)個電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)器。這些電(dian)(dian)(dian)(dian)池(chi)(chi)通(tong)常都為鋰離子電(dian)(dian)(dian)(dian)池(chi)(chi)，并且其功(gong)率(lv)密度(du)可在范圍400mA小(xiao)時(shi)(shi)(shi)到1.5A小(xiao)時(shi)(shi)(shi)變化。你可以使用(yong)一(yi)(yi)種(zhong)線性(xing)充(chong)(chong)電(dian)(dian)(dian)(dian)器給這種(zhong)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)，而且這種(zhong)充(chong)(chong)電(dian)(dian)(dian)(dian)器通(tong)常比(bi)基于轉換器的方(fang)案在外形上明顯更小(xiao)，操作更簡便，成本更低，但它(ta)有(you)一(yi)(yi)個主要缺點：能(neng)耗太高(gao)(gao)。當輸入電(dian)(dian)(dian)(dian)壓為高(gao)(gao)和電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓為低(已放(fang)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)(chi))時(shi)(shi)(shi)，線性(xing)充(chong)(chong)電(dian)(dian)(dian)(dian)器產生的熱(re)量(liang)足以損壞自身(shen)或其它(ta)鄰近元件。典(dian)型地(di)，這種(zhong)狀態(tai)(即電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓隨充(chong)(chong)電(dian)(dian)(dian)(dian)的進行而升高(gao)(gao))只是暫時(shi)(shi)(shi)現象，但正是這些最糟(zao)糕的狀態(tai)需(xu)要設計師在決定充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流與IC溫度(du)的最大容許(xu)值時(shi)(shi)(shi)必須充(chong)(chong)分地(di)加以考慮(lv)。當然，一(yi)(yi)種(zhong)解決這種(zhong)過(guo)熱(re)問題的簡單方(fang)法是降低充(chong)(chong)電(dian)(dian)(dian)(dian)過(guo)程中整個恒流段的充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流，但這種(zhong)方(fang)法伴隨的問題是充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)(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(bu)功(gong)率(lv)MOSFET允(yun)許編程設定的(de)(de)最大充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)可(ke)(ke)達1.5A，精(jing)度(du)為(wei)(wei)(wei)7%，以(yi)(yi)確保充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)快速和完全。這種內部(bu)MOSFET還可(ke)(ke)省(sheng)掉一個(ge)外部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)敏感(gan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)或(huo)遏流(liu)二極管，最終的(de)(de)無負載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)是(shi)(shi)引腳可(ke)(ke)選(xuan)的(de)(de)，或(huo)為(wei)(wei)(wei)4.1V或(huo)為(wei)(wei)(wei) 4.2V，精(jing)度(du)是(shi)(shi)1%，這可(ke)(ke)防止過充(chong)(chong)(chong)(chong)(chong)帶(dai)來的(de)(de)危(wei)險(xian)或(huo)欠充(chong)(chong)(chong)(chong)(chong)造(zao)成的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)容量不足。遵從電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)制造(zao)商的(de)(de)使用要(yao)求，LTC1733包含了一個(ge)可(ke)(ke)編程充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)終止定時器和熱敏電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)輸(shu)入(ru)，以(yi)(yi)保證(zheng)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)全過程的(de)(de)溫度(du)符合要(yao)求。狀態輸(shu)出包括：用以(yi)(yi)指示充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)后(hou)期狀態的(de)(de)C/10充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)檢(jian)測、決(jue)定充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)是(shi)(shi)否可(ke)(ke)以(yi)(yi)進行下(xia)去的(de)(de)壁式(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源適配(pei)器狀態檢(jian)測、充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)監測、以(yi)(yi)及(ji)用以(yi)(yi)識別壞電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)錯誤檢(jian)測。低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)調理電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(滴充(chong)(chong)(chong)(chong)(chong))可(ke)(ke)安全地(di)為(wei)(wei)(wei)過放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，并自動續充(chong)(chong)(chong)(chong)(chong)以(yi)(yi)確保電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)總能(neng)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)完全。當沒有壁式(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源適配(pei)器或(huo)該部(bu)件關(guan)閉(bi)的(de)(de)時候，為(wei)(wei)(wei)保持電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)能(neng)量， LTC1733的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)漏電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)降(jiang)到5(A以(yi)(yi)下(xia)。

　　給電池充電
　　給單電(dian)(dian)(dian)池鋰離子電(dian)(dian)(dian)池系統充電(dian)(dian)(dian)時，用(yong)戶(hu)須在VCC腳處施加至少4.5V的(de)輸入(ru)電(dian)(dian)(dian)壓。ACPR腳隨后(hou)降為低(di)電(dian)(dian)(dian)平(pull low)，指示輸入(ru)電(dian)(dian)(dian)壓條件已滿(man)足(見圖2)。此外，必(bi)須用(yong)一個1%的(de)電(dian)(dian)(dian)阻器(qi)把PROG與GND相連(lian)，使額(e)定充電(dian)(dian)(dian)電(dian)(dian)(dian)流設定為100V/RPROG。而(er)后(hou)CHPG腳為低(di)電(dian)(dian)(dian)平，指示充電(dian)(dian)(dian)循環開始。TIMER和GND之間(jian)(jian)用(yong)電(dian)(dian)(dian)容(rong)器(qi)連(lian)接，充電(dian)(dian)(dian)終(zhong)止時間(jian)(jian)設定為3小時/100nF。

　　如(ru)果在(zai)充電(dian)(dian)(dian)(dian)(dian)循環開始(shi)時BAT腳的(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低于2.48V，那(nei)么，充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流將為設定(ding)值的(de)1/10，以使(shi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)足(zu)夠(gou)高，安全(quan)實現(xian)全(quan)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流充電(dian)(dian)(dian)(dian)(dian)(見圖3)。如(ru)果電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)損壞，且在(zai)1/4的(de)設定(ding)終止(zhi)時間內電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)都升不到2.48V以上，則充電(dian)(dian)(dian)(dian)(dian)循環終止(zhi)，且FAULT狀(zhuang)態輸(shu)出(chu)將鎖存(cun)為低電(dian)(dian)(dian)(dian)(dian)平，指示電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)已(yi)壞。ACPR、CHRG和(he)FAULT三個(ge)狀(zhuang)態輸(shu)出(chu)腳全(quan)都產(chan)生(sheng)足(zu)夠(gou)的(de)電(dian)(dian)(dian)(dian)(dian)流衰弱量，使(shi)LED亮燈。一(yi)旦電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)升到2.48V以上(充電(dian)(dian)(dian)(dian)(dian)循環開始(shi)后不久(jiu)會明顯(xian)表現(xian)出(chu)來)，LTC1733將為電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)提(ti)供(gong)由RPROG設定(ding)的(de)恒(heng)定(ding)電(dian)(dian)(dian)(dian)(dian)流。LTC1733將一(yi)直(zhi)保(bao)持恒(heng)流模式，直(zhi)到BAT腳的(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)接近所選擇(ze)的(de)最終浮(fu)置電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(SEL=0V時為 4.1V ，SEL=VCC時為4.2V)為止(zhi)。此(ci)后，器件(jian)進入(ru)恒(heng)壓(ya)(ya)模式。

　　在恒壓模(mo)式下(xia)，LTC1733將開(kai)始降(jiang)低(di)充電(dian)電(dian)流(liu)以保持BAT腳的恒壓而非恒流(liu)輸(shu)出。當電(dian)流(liu)降(jiang)至最大設(she)定(ding)充電(dian)電(dian)流(liu)的10%時，內部比較器會斷(duan)開(kai)CHRG腳，并將一弱電(dian)流(liu)源(約25(A)接地，以顯(xian)示接近充電(dian)結束(C/10)狀態。

　　與電流達到C/10時便結束充電過程的電池充電器不(bu)同，LTC1733在(zai)到達C/10點(dian)后(hou)，只要終止定時器時間不(bu)到，會繼續給電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)，以(yi)保證電(dian)(dian)(dian)池(chi)完全充(chong)(chong)滿(man)。在(zai)C/10處終止充(chong)(chong)電(dian)(dian)(dian)過程使電(dian)(dian)(dian)池(chi)只能(neng)充(chong)(chong)到其容量(liang)的90%到95%，而在(zai)C/10后(hou)繼續充(chong)(chong)并按時間要求(qiu)結(jie)束(shu)可(ke)使電(dian)(dian)(dian)池(chi)的容量(liang)充(chong)(chong)到100%。一(yi)旦充(chong)(chong)電(dian)(dian)(dian)結(jie)束(shu)，CHRG腳便(bian)呈現高(gao)阻抗(kang)狀(zhuang)態。

    電池的再充電
    假定在第一(yi)次充電(dian)(dian)(dian)(dian)(dian)(dian)時，電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓已充到(dao)了3.95V(SEL = 0V時) 或(huo)4.05V (SEL = VCC時)以上，那么LTC1733可(ke)對電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)進(jin)行再充電(dian)(dian)(dian)(dian)(dian)(dian)。一(yi)旦超出這些閾值，如果電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓因電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)負載的(de)存在或(huo)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)自(zi)放電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流而(er)掉到(dao)3.9V (SEL = 0V)或(huo)4.0V (SEL = VCC)以下(xia)時，則新一(yi)輪的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)循(xun)環開始了。再充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)路集(ji)結(jie)BAT腳電(dian)(dian)(dian)(dian)(dian)(dian)壓數(shu)毫(hao)秒，以防止充電(dian)(dian)(dian)(dian)(dian)(dian)循(xun)環重啟造成的(de)瞬態沖(chong)擊。

    熱調節
　　LTC1733的(de)(de)另(ling)一(yi)個特性是具有內部熱調節回路。如果高(gao)功率操作(zuo)或高(gao)的(de)(de)環境(jing)溫度導(dao)致LTC1733的(de)(de)溫度接(jie)近105(C，那么充(chong)電(dian)電(dian)流會自動(dong)降低(di)以將溫度保持在105(C左右 (板溫度通常低(di)于85(C)，這便是所謂的(de)(de)恒溫模式。這一(yi)特性允許用戶基于具體的(de)(de)工作(zuo)條(tiao)件設定(ding)充(chong)電(dian)電(dian)流，并(bing)去掉許多線性應用必需的(de)(de)復雜過熱保護設計。

　　LTC1733會自動監(jian)視最糟狀態，這(zhe)一特性(xing)除可保(bao)護(hu)LTC1733外，還能去除板(ban)上的“熱(re)點(dian)”區，從(cong)而保(bao)護(hu)周(zhou)邊(bian)元件。其它的電(dian)池充(chong)電(dian)器，其熱(re)關(guan)閉特性(xing)只是簡單地(di)在極高溫(wen)(wen)(wen)度(du)下(xia)(一般是150(C)關(guan)閉充(chong)電(dian)器而已。這(zhe)種基于(yu)溫(wen)(wen)(wen)度(du)的關(guan)閉特性(xing)允許電(dian)池充(chong)電(dian)器和(he)周(zhou)邊(bian)PCB板(ban)溫(wen)(wen)(wen)度(du)升至非常高，盡管具備關(guan)閉“保(bao)護(hu)”功能，但必須對應用(yong)進行仔細設計(ji)(ji)以避免到達(da)熱(re)關(guan)閉溫(wen)(wen)(wen)度(du)。LTC1733通過自動均(jun)衡充(chong)電(dian)電(dian)流、散熱(re)和(he)工作溫(wen)(wen)(wen)度(du)，可使設計(ji)(ji)得(de)到簡化。

　　為進一(yi)(yi)步改進LTC1733的(de)(de)熱(re)調節(jie)性能(neng)，它(ta)采用(yong)了熱(re)增強型(xing)MSOP封(feng)裝(zhuang)。其(qi)占用(yong)板面積(ji)可做到(dao)(dao)小于72 mm2，室溫功耗(hao)2W。這(zhe)相當(dang)于用(yong)5V輸入電(dian)(dian)(dian)源實(shi)現最大充電(dian)(dian)(dian)電(dian)(dian)(dian)流1.5A。這(zhe)里假定(ding)鋰(li)(li)離子(zi)(zi)(zi)電(dian)(dian)(dian)池(chi)在充電(dian)(dian)(dian)大部分時(shi)間里處于(3.7V狀態。實(shi)際(ji)上(shang)，由(you)于典型(xing)的(de)(de)鋰(li)(li)離子(zi)(zi)(zi)電(dian)(dian)(dian)池(chi)在充電(dian)(dian)(dian)開始幾分鐘內便升到(dao)(dao)3.8V以上(shang)，因此(ci)這(zhe)一(yi)(yi)假定(ding)有些保守(shou)。LTC1733的(de)(de)這(zhe)一(yi)(yi)獨特熱(re)特性和(he)7%的(de)(de)設定(ding)充電(dian)(dian)(dian)電(dian)(dian)(dian)流精(jing)度，使單電(dian)(dian)(dian)池(chi)鋰(li)(li)離子(zi)(zi)(zi)電(dian)(dian)(dian)池(chi)系(xi)統(tong)的(de)(de)充電(dian)(dian)(dian)過程非常迅(xun)速和(he)精(jing)確。

　　PROG電流監控器
　　在(zai)恒流(liu)(liu)模式下，PROG腳(jiao)(jiao)(jiao)(jiao)的(de)電壓(ya)總為1.5V，指示設定的(de)充電電流(liu)(liu)從BAT腳(jiao)(jiao)(jiao)(jiao)流(liu)(liu)出。在(zai)恒溫或恒壓(ya)模式下，BAT腳(jiao)(jiao)(jiao)(jiao)的(de)電流(liu)(liu)有所下降。PROG腳(jiao)(jiao)(jiao)(jiao)與三個開漏狀態輸出(ACPR、CHRG和 FAULT)時刻通告(gao)用戶(hu)LTC1733到底在(zai)做什么。

　　NTC熱敏電阻
　　除了可(ke)(ke)編程(cheng)定(ding)時(shi)(shi)器(qi)和(he)低的(de)電(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)限(xian)(xian)定(ding)條件外，LTC1733在推薦給電(dian)(dian)(dian)(dian)池(chi)制(zhi)造(zao)商(shang)的(de)安全性特性列表中還增(zeng)加了充電(dian)(dian)(dian)(dian)時(shi)(shi)的(de)溫(wen)(wen)(wen)度限(xian)(xian)定(ding)。電(dian)(dian)(dian)(dian)池(chi)溫(wen)(wen)(wen)度通過緊貼電(dian)(dian)(dian)(dian)池(chi)組放置一只負溫(wen)(wen)(wen)度系數(NTC)熱(re)敏電(dian)(dian)(dian)(dian)阻來測定(ding)。借(jie)助IC中的(de)內(nei)部(bu)溫(wen)(wen)(wen)度限(xian)(xian)制(zhi)電(dian)(dian)(dian)(dian)路，LTC1733在電(dian)(dian)(dian)(dian)池(chi)溫(wen)(wen)(wen)度降到(dao)0(C以(yi)下(xia)或升到(dao)50(C以(yi)上時(shi)(shi)，可(ke)(ke)臨時(shi)(shi)停(ting)住內(nei)部(bu)定(ding)時(shi)(shi)器(qi)并停(ting)止充電(dian)(dian)(dian)(dian)。實施這一功能，選用RHOT的(de)電(dian)(dian)(dian)(dian)阻值應與50(C下(xia)所用熱(re)敏電(dian)(dian)(dian)(dian)阻的(de)阻值相(xiang)(xiang)同。這樣(yang)將可(ke)(ke)以(yi)確保內(nei)部(bu)比較器(qi)的(de)1/2VCC摔(shuai)點(trip point)與NTC的(de)50(C溫(wen)(wen)(wen)度相(xiang)(xiang)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：