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，目前通常使用(yong)一種(zhong)(zhong)線性充(chong)(chong)電(dian)(dian)器(qi)(qi)給這種(zhong)(zhong)電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)，但(dan)(dan)這種(zhong)(zhong)充(chong)(chong)電(dian)(dian)器(qi)(qi)盡(jin)管操作更簡便和成本(ben)更低(di)，但(dan)(dan)它(ta)(ta)(ta)有一個主(zhu)要缺點(dian)：能(neng)耗太高。當(dang)輸入電(dian)(dian)壓為高和電(dian)(dian)池(chi)電(dian)(dian)壓為低(di)(已放電(dian)(dian)電(dian)(dian)池(chi))時，線性充(chong)(chong)電(dian)(dian)器(qi)(qi)產生的熱量(liang)足(zu)以損壞自身或其它(ta)(ta)(ta)鄰(lin)近元件。在本(ben)文中，凌(ling)特技術公(gong)司提(ti)出了(le)一種(zhong)(zhong)替代方案，它(ta)(ta)(ta)可解決所有的過熱問題而且充(chong)(chong)電(dian)(dian)快(kuai)速。

　　當(dang)(dang)今許多靠電(dian)(dian)(dian)池(chi)供(gong)電(dian)(dian)(dian)的(de)(de)(de)手持設備都內建(jian)有一個(ge)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)器(qi)(qi)。這(zhe)些電(dian)(dian)(dian)池(chi)通常都為(wei)鋰離子電(dian)(dian)(dian)池(chi)，并且其(qi)功率(lv)密度可在范圍400mA小(xiao)時(shi)(shi)到1.5A小(xiao)時(shi)(shi)變化。你可以(yi)使用一種(zhong)(zhong)(zhong)線性充(chong)電(dian)(dian)(dian)器(qi)(qi)給這(zhe)種(zhong)(zhong)(zhong)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)，而且這(zhe)種(zhong)(zhong)(zhong)充(chong)電(dian)(dian)(dian)器(qi)(qi)通常比基于(yu)轉換器(qi)(qi)的(de)(de)(de)方案在外形上明顯更(geng)小(xiao)，操作更(geng)簡便，成本更(geng)低，但(dan)它有一個(ge)主要(yao)缺(que)點(dian)：能(neng)耗太高(gao)(gao)。當(dang)(dang)輸入電(dian)(dian)(dian)壓為(wei)高(gao)(gao)和電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓為(wei)低(已放(fang)電(dian)(dian)(dian)電(dian)(dian)(dian)池(chi))時(shi)(shi)，線性充(chong)電(dian)(dian)(dian)器(qi)(qi)產(chan)生(sheng)的(de)(de)(de)熱量足以(yi)損(sun)壞自(zi)身或其(qi)它鄰近元(yuan)件。典型地(di)，這(zhe)種(zhong)(zhong)(zhong)狀(zhuang)態(tai)(即電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓隨充(chong)電(dian)(dian)(dian)的(de)(de)(de)進行而升高(gao)(gao))只(zhi)是(shi)暫時(shi)(shi)現象，但(dan)正是(shi)這(zhe)些最(zui)糟糕的(de)(de)(de)狀(zhuang)態(tai)需(xu)要(yao)設計(ji)師(shi)在決(jue)定(ding)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流與(yu)IC溫度的(de)(de)(de)最(zui)大容許值時(shi)(shi)必須充(chong)分地(di)加以(yi)考慮。當(dang)(dang)然，一種(zhong)(zhong)(zhong)解決(jue)這(zhe)種(zhong)(zhong)(zhong)過熱問(wen)(wen)題的(de)(de)(de)簡單方法(fa)是(shi)降低充(chong)電(dian)(dian)(dian)過程中整個(ge)恒流段的(de)(de)(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流，但(dan)這(zhe)種(zhong)(zhong)(zhong)方法(fa)伴隨的(de)(de)(de)問(wen)(wen)題是(shi)充(chong)電(dian)(dian)(dian)時(shi)(shi)間的(de)(de)(de)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(yi)個(ge)內(nei)(nei)部功率(lv)MOSFET允許編(bian)程(cheng)設定的(de)(de)最大充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流可達1.5A，精度為7%，以確(que)保充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)快(kuai)速(su)和完(wan)全(quan)(quan)。這(zhe)種(zhong)內(nei)(nei)部MOSFET還可省(sheng)掉(diao)一(yi)個(ge)外部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流敏感(gan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻或(huo)遏(e)流二極管，最終的(de)(de)無(wu)負載(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓是引腳(jiao)可選的(de)(de)，或(huo)為4.1V或(huo)為 4.2V，精度是1%，這(zhe)可防止(zhi)過充(chong)帶(dai)來的(de)(de)危險(xian)或(huo)欠充(chong)造成的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)容量(liang)(liang)不足。遵從電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)制(zhi)造商的(de)(de)使用要求，LTC1733包含(han)了一(yi)個(ge)可編(bian)程(cheng)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)終止(zhi)定時(shi)器和熱敏電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻輸(shu)(shu)入，以保證充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)全(quan)(quan)過程(cheng)的(de)(de)溫(wen)度符(fu)合要求。狀態(tai)輸(shu)(shu)出包括：用以指示(shi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)后期狀態(tai)的(de)(de)C/10充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)檢(jian)測(ce)(ce)、決定充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)是否可以進行下(xia)去的(de)(de)壁式(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源適配(pei)(pei)器狀態(tai)檢(jian)測(ce)(ce)、充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流監測(ce)(ce)、以及用以識別(bie)壞電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)錯誤檢(jian)測(ce)(ce)。低電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)調理(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(滴充(chong))可安全(quan)(quan)地為過放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，并自動續充(chong)以確(que)保電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)總能充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)完(wan)全(quan)(quan)。當沒有壁式(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源適配(pei)(pei)器或(huo)該部件關閉的(de)(de)時(shi)候(hou)，為保持電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)能量(liang)(liang)， LTC1733的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)漏電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流降到5(A以下(xia)。

　　給電池充電
　　給單電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)鋰離子電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)系(xi)統充電(dian)(dian)(dian)(dian)(dian)(dian)時，用(yong)戶須(xu)在VCC腳(jiao)(jiao)處施加至少(shao)4.5V的(de)輸入電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)。ACPR腳(jiao)(jiao)隨后(hou)降為低(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)平(pull low)，指(zhi)示(shi)輸入電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)條件(jian)已滿足(見圖2)。此外(wai)，必須(xu)用(yong)一個1%的(de)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)器把(ba)PROG與GND相連，使額定充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流設定為100V/RPROG。而后(hou)CHPG腳(jiao)(jiao)為低(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)平，指(zhi)示(shi)充電(dian)(dian)(dian)(dian)(dian)(dian)循環開始。TIMER和GND之間(jian)用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)容器連接(jie)，充電(dian)(dian)(dian)(dian)(dian)(dian)終止時間(jian)設定為3小(xiao)時/100nF。

　　如(ru)(ru)果在充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)循(xun)環(huan)開始時BAT腳(jiao)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低于2.48V，那么(me)，充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流將為設(she)定(ding)(ding)(ding)值的(de)(de)1/10，以(yi)使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)足(zu)夠高，安全(quan)實現全(quan)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(見圖3)。如(ru)(ru)果電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池損壞(huai)，且在1/4的(de)(de)設(she)定(ding)(ding)(ding)終止時間內電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)都升不到2.48V以(yi)上，則充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)循(xun)環(huan)終止，且FAULT狀(zhuang)態(tai)輸(shu)出(chu)將鎖(suo)存為低電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平，指示電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池已(yi)壞(huai)。ACPR、CHRG和FAULT三個狀(zhuang)態(tai)輸(shu)出(chu)腳(jiao)全(quan)都產(chan)生(sheng)足(zu)夠的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流衰弱量，使(shi)LED亮燈。一(yi)旦電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)升到2.48V以(yi)上(充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)循(xun)環(huan)開始后不久會明顯表現出(chu)來)，LTC1733將為電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池提供由RPROG設(she)定(ding)(ding)(ding)的(de)(de)恒(heng)定(ding)(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流。LTC1733將一(yi)直保(bao)持恒(heng)流模式(shi)，直到BAT腳(jiao)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)接(jie)近所選擇(ze)的(de)(de)最終浮置(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(SEL=0V時為 4.1V ，SEL=VCC時為4.2V)為止。此后，器件進入恒(heng)壓(ya)(ya)模式(shi)。

　　在恒(heng)壓(ya)模式下，LTC1733將開始降(jiang)低充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)以(yi)保持BAT腳的(de)恒(heng)壓(ya)而非恒(heng)流(liu)輸出。當電(dian)(dian)(dian)流(liu)降(jiang)至(zhi)最大設(she)定充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)的(de)10%時，內(nei)部比較(jiao)器(qi)會斷(duan)開CHRG腳，并將一(yi)弱(ruo)電(dian)(dian)(dian)流(liu)源(約25(A)接地，以(yi)顯示(shi)接近充(chong)電(dian)(dian)(dian)結束(shu)(C/10)狀(zhuang)態。

　　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)到達C/10點后，只(zhi)要終止定時器時間(jian)不到，會繼續給電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)，以保證電(dian)(dian)(dian)(dian)池(chi)完(wan)全充(chong)(chong)滿。在(zai)C/10處終止充(chong)(chong)電(dian)(dian)(dian)(dian)過程使電(dian)(dian)(dian)(dian)池(chi)只(zhi)能充(chong)(chong)到其容量的(de)90%到95%，而在(zai)C/10后繼續充(chong)(chong)并按(an)時間(jian)要求結(jie)束可使電(dian)(dian)(dian)(dian)池(chi)的(de)容量充(chong)(chong)到100%。一旦充(chong)(chong)電(dian)(dian)(dian)(dian)結(jie)束，CHRG腳便呈(cheng)現高阻(zu)抗狀態(tai)。

    電池的再充電
    假(jia)定在第一次充(chong)(chong)電(dian)時(shi)(shi)，電(dian)池(chi)電(dian)壓(ya)已(yi)充(chong)(chong)到了3.95V(SEL = 0V時(shi)(shi)) 或(huo)4.05V (SEL = VCC時(shi)(shi))以(yi)上(shang)，那么(me)LTC1733可對(dui)電(dian)池(chi)進行再充(chong)(chong)電(dian)。一旦超出這些閾值，如果電(dian)池(chi)電(dian)壓(ya)因電(dian)池(chi)負載(zai)的(de)存在或(huo)電(dian)池(chi)的(de)自放電(dian)電(dian)流而掉到3.9V (SEL = 0V)或(huo)4.0V (SEL = VCC)以(yi)下時(shi)(shi)，則新(xin)一輪的(de)充(chong)(chong)電(dian)循環(huan)開始(shi)了。再充(chong)(chong)電(dian)電(dian)路集結BAT腳電(dian)壓(ya)數毫秒，以(yi)防止充(chong)(chong)電(dian)循環(huan)重啟造(zao)成的(de)瞬態沖擊。

    熱調節
　　LTC1733的另一個特(te)性是(shi)具有內部(bu)熱調節回路。如果高功率(lv)操作或高的環境溫度導(dao)致LTC1733的溫度接近105(C，那么充電(dian)電(dian)流會(hui)自動(dong)降(jiang)低以將溫度保持在105(C左右(you) (板溫度通常低于(yu)85(C)，這便是(shi)所謂的恒(heng)溫模式(shi)。這一特(te)性允許(xu)用(yong)戶(hu)基于(yu)具體的工作條(tiao)件設定充電(dian)電(dian)流，并去(qu)掉(diao)許(xu)多線性應(ying)用(yong)必需的復雜過熱保護設計。

　　LTC1733會自動監視最糟狀態，這一特(te)性(xing)除(chu)可保(bao)(bao)護LTC1733外，還能去除(chu)板上的“熱(re)點(dian)”區(qu)，從而保(bao)(bao)護周邊元件。其它(ta)的電(dian)池充電(dian)器，其熱(re)關(guan)(guan)閉(bi)(bi)特(te)性(xing)只(zhi)是簡(jian)(jian)單地(di)在極高溫(wen)度(du)(du)下(一般是150(C)關(guan)(guan)閉(bi)(bi)充電(dian)器而已。這種基于溫(wen)度(du)(du)的關(guan)(guan)閉(bi)(bi)特(te)性(xing)允(yun)許電(dian)池充電(dian)器和(he)周邊PCB板溫(wen)度(du)(du)升至非(fei)常高，盡(jin)管具(ju)備(bei)關(guan)(guan)閉(bi)(bi)“保(bao)(bao)護”功能，但必須對應(ying)用進行仔細設計以避免到達熱(re)關(guan)(guan)閉(bi)(bi)溫(wen)度(du)(du)。LTC1733通過自動均衡充電(dian)電(dian)流、散熱(re)和(he)工作(zuo)溫(wen)度(du)(du)，可使設計得(de)到簡(jian)(jian)化。

　　為進一步改(gai)進LTC1733的(de)熱(re)調(diao)節性能，它(ta)采用了熱(re)增(zeng)強型MSOP封裝。其(qi)占用板面積(ji)可做到小于72 mm2，室溫功(gong)耗2W。這(zhe)(zhe)相當于用5V輸入電源(yuan)實現最大充(chong)電電流(liu)1.5A。這(zhe)(zhe)里假定(ding)鋰離子(zi)電池在充(chong)電大部分時間里處于(3.7V狀(zhuang)態。實際上，由于典型的(de)鋰離子(zi)電池在充(chong)電開始幾分鐘內(nei)便(bian)升到3.8V以上，因此(ci)這(zhe)(zhe)一假定(ding)有些保守。LTC1733的(de)這(zhe)(zhe)一獨特熱(re)特性和7%的(de)設定(ding)充(chong)電電流(liu)精(jing)度(du)，使單電池鋰離子(zi)電池系統的(de)充(chong)電過(guo)程(cheng)非常迅速和精(jing)確。

　　PROG電流監控器
　　在恒(heng)流(liu)模式下(xia)(xia)，PROG腳(jiao)的(de)電壓總為1.5V，指示設定的(de)充(chong)電電流(liu)從BAT腳(jiao)流(liu)出。在恒(heng)溫或恒(heng)壓模式下(xia)(xia)，BAT腳(jiao)的(de)電流(liu)有所下(xia)(xia)降。PROG腳(jiao)與三個開漏狀態輸(shu)出(ACPR、CHRG和 FAULT)時刻(ke)通告用戶LTC1733到底在做什么。

　　NTC熱敏電阻
　　除了可(ke)編程定時(shi)(shi)器(qi)和低的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)限(xian)定條件(jian)外，LTC1733在(zai)推(tui)薦(jian)給(gei)電(dian)(dian)(dian)(dian)池(chi)(chi)制(zhi)造商的(de)安全(quan)性特(te)性列表中(zhong)還增加了充(chong)電(dian)(dian)(dian)(dian)時(shi)(shi)的(de)溫度(du)(du)限(xian)定。電(dian)(dian)(dian)(dian)池(chi)(chi)溫度(du)(du)通過緊貼電(dian)(dian)(dian)(dian)池(chi)(chi)組放置一(yi)只負溫度(du)(du)系(xi)數(shu)(NTC)熱敏(min)電(dian)(dian)(dian)(dian)阻來測定。借助IC中(zhong)的(de)內部溫度(du)(du)限(xian)制(zhi)電(dian)(dian)(dian)(dian)路，LTC1733在(zai)電(dian)(dian)(dian)(dian)池(chi)(chi)溫度(du)(du)降到(dao)0(C以(yi)下或升到(dao)50(C以(yi)上(shang)時(shi)(shi)，可(ke)臨時(shi)(shi)停住內部定時(shi)(shi)器(qi)并(bing)停止充(chong)電(dian)(dian)(dian)(dian)。實施這(zhe)一(yi)功能，選用RHOT的(de)電(dian)(dian)(dian)(dian)阻值應(ying)與50(C下所用熱敏(min)電(dian)(dian)(dian)(dian)阻的(de)阻值相(xiang)同。這(zhe)樣將可(ke)以(yi)確保內部比較器(qi)的(de)1/2VCC摔點(trip point)與NTC的(de)50(C溫度(du)(du)相(xiang)對應(ying)。

　　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(xing)能概要(yao)：