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(qian)通常使(shi)用一種線性(xing)充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)給(gei)這(zhe)種電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)，但(dan)這(zhe)種充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)盡(jin)管操(cao)作更簡便和成本更低，但(dan)它(ta)有一個主要缺點(dian)：能耗太(tai)高(gao)。當輸入電(dian)(dian)(dian)(dian)壓為高(gao)和電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓為低(已放電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi))時，線性(xing)充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)產生(sheng)的(de)熱(re)量足以損(sun)壞(huai)自身或其它(ta)鄰近元(yuan)件(jian)。在本文中，凌特技術公司(si)提出了一種替代方案，它(ta)可(ke)解決所有的(de)過熱(re)問題而且充(chong)電(dian)(dian)(dian)(dian)快速。

　　當今許多靠電(dian)(dian)池供(gong)電(dian)(dian)的(de)(de)(de)(de)手(shou)持(chi)設備(bei)都內建(jian)有(you)一(yi)個(ge)電(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)器(qi)。這(zhe)些電(dian)(dian)池通(tong)常(chang)都為鋰離子電(dian)(dian)池，并且其功率密度可在(zai)范圍(wei)400mA小時(shi)(shi)到1.5A小時(shi)(shi)變化。你可以使用一(yi)種線(xian)性(xing)(xing)充(chong)(chong)(chong)電(dian)(dian)器(qi)給這(zhe)種電(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)，而(er)且這(zhe)種充(chong)(chong)(chong)電(dian)(dian)器(qi)通(tong)常(chang)比(bi)基于轉(zhuan)換器(qi)的(de)(de)(de)(de)方案(an)在(zai)外形上明顯更小，操作(zuo)更簡(jian)便，成(cheng)本更低，但它有(you)一(yi)個(ge)主要(yao)缺點：能耗太高(gao)。當輸入(ru)電(dian)(dian)壓為高(gao)和電(dian)(dian)池電(dian)(dian)壓為低(已放(fang)電(dian)(dian)電(dian)(dian)池)時(shi)(shi)，線(xian)性(xing)(xing)充(chong)(chong)(chong)電(dian)(dian)器(qi)產(chan)生的(de)(de)(de)(de)熱(re)(re)量足以損壞自(zi)身或其它鄰近元件(jian)。典型地，這(zhe)種狀態(即電(dian)(dian)池電(dian)(dian)壓隨充(chong)(chong)(chong)電(dian)(dian)的(de)(de)(de)(de)進行(xing)而(er)升高(gao))只(zhi)是(shi)(shi)暫時(shi)(shi)現象，但正是(shi)(shi)這(zhe)些最(zui)糟(zao)糕的(de)(de)(de)(de)狀態需要(yao)設計(ji)師在(zai)決定(ding)充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)與IC溫度的(de)(de)(de)(de)最(zui)大容許值(zhi)時(shi)(shi)必(bi)須(xu)充(chong)(chong)(chong)分地加(jia)以考慮。當然(ran)，一(yi)種解決這(zhe)種過熱(re)(re)問(wen)題(ti)的(de)(de)(de)(de)簡(jian)單方法是(shi)(shi)降低充(chong)(chong)(chong)電(dian)(dian)過程中整個(ge)恒流(liu)段的(de)(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)，但這(zhe)種方法伴隨的(de)(de)(de)(de)問(wen)題(ti)是(shi)(shi)充(chong)(chong)(chong)電(dian)(dian)時(shi)(shi)間(jian)的(de)(de)(de)(de)相應延(yan)長(chang)。

　　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允許編程(cheng)設定(ding)的(de)(de)最大充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)可(ke)達(da)1.5A，精(jing)度(du)為(wei)7%，以(yi)確(que)保(bao)(bao)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)快(kuai)速和完全(quan)(quan)。這種內部MOSFET還可(ke)省掉一個(ge)外部電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)敏感電(dian)(dian)(dian)(dian)(dian)阻或(huo)(huo)(huo)遏流(liu)(liu)(liu)(liu)二極(ji)管(guan)，最終(zhong)的(de)(de)無(wu)負載電(dian)(dian)(dian)(dian)(dian)壓是引腳可(ke)選的(de)(de)，或(huo)(huo)(huo)為(wei)4.1V或(huo)(huo)(huo)為(wei) 4.2V，精(jing)度(du)是1%，這可(ke)防止(zhi)過充(chong)(chong)(chong)帶來的(de)(de)危(wei)險或(huo)(huo)(huo)欠(qian)充(chong)(chong)(chong)造成的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)容量(liang)不足(zu)。遵從(cong)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)制造商的(de)(de)使用要求，LTC1733包含了一個(ge)可(ke)編程(cheng)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)終(zhong)止(zhi)定(ding)時(shi)器和熱敏電(dian)(dian)(dian)(dian)(dian)阻輸(shu)入，以(yi)保(bao)(bao)證充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)全(quan)(quan)過程(cheng)的(de)(de)溫度(du)符合(he)要求。狀(zhuang)態輸(shu)出包括：用以(yi)指(zhi)示(shi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)后期狀(zhuang)態的(de)(de)C/10充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)檢測(ce)(ce)、決定(ding)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)是否可(ke)以(yi)進行(xing)下(xia)去的(de)(de)壁式電(dian)(dian)(dian)(dian)(dian)源適配器狀(zhuang)態檢測(ce)(ce)、充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)監測(ce)(ce)、以(yi)及用以(yi)識別(bie)壞電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)錯誤檢測(ce)(ce)。低(di)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)調理電(dian)(dian)(dian)(dian)(dian)路(滴充(chong)(chong)(chong))可(ke)安全(quan)(quan)地為(wei)過放電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，并自動續充(chong)(chong)(chong)以(yi)確(que)保(bao)(bao)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)總能(neng)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)完全(quan)(quan)。當沒有壁式電(dian)(dian)(dian)(dian)(dian)源適配器或(huo)(huo)(huo)該部件關閉的(de)(de)時(shi)候，為(wei)保(bao)(bao)持電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)能(neng)量(liang)， LTC1733的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)漏電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)降(jiang)到5(A以(yi)下(xia)。

　　給電池充電
　　給單電池鋰(li)離子電池系統(tong)充(chong)(chong)電時，用戶(hu)須在VCC腳(jiao)(jiao)處施加至少4.5V的(de)輸入電壓。ACPR腳(jiao)(jiao)隨后降為低(di)電平(pull low)，指示(shi)輸入電壓條件已滿足(見圖2)。此外，必須用一(yi)個1%的(de)電阻器把PROG與GND相連(lian)，使額定(ding)充(chong)(chong)電電流設定(ding)為100V/RPROG。而后CHPG腳(jiao)(jiao)為低(di)電平，指示(shi)充(chong)(chong)電循環(huan)開(kai)始。TIMER和(he)GND之間用電容(rong)器連(lian)接，充(chong)(chong)電終止時間設定(ding)為3小時/100nF。

　　如果在充(chong)電(dian)(dian)循環開(kai)始(shi)時BAT腳的電(dian)(dian)壓低于(yu)2.48V，那么(me)，充(chong)電(dian)(dian)電(dian)(dian)流(liu)將為設(she)定(ding)(ding)值(zhi)的1/10，以(yi)使電(dian)(dian)池(chi)(chi)電(dian)(dian)壓足夠高(gao)，安(an)全實現(xian)全充(chong)電(dian)(dian)電(dian)(dian)流(liu)充(chong)電(dian)(dian)(見圖3)。如果電(dian)(dian)池(chi)(chi)損壞，且在1/4的設(she)定(ding)(ding)終止時間內電(dian)(dian)壓都(dou)升(sheng)不到(dao)2.48V以(yi)上(shang)，則充(chong)電(dian)(dian)循環終止，且FAULT狀態(tai)輸出(chu)(chu)將鎖(suo)存為低電(dian)(dian)平，指示電(dian)(dian)池(chi)(chi)已(yi)壞。ACPR、CHRG和FAULT三個狀態(tai)輸出(chu)(chu)腳全都(dou)產(chan)生足夠的電(dian)(dian)流(liu)衰弱量，使LED亮(liang)燈。一(yi)旦電(dian)(dian)池(chi)(chi)電(dian)(dian)壓升(sheng)到(dao)2.48V以(yi)上(shang)(充(chong)電(dian)(dian)循環開(kai)始(shi)后(hou)不久會明顯表現(xian)出(chu)(chu)來)，LTC1733將為電(dian)(dian)池(chi)(chi)提供由(you)RPROG設(she)定(ding)(ding)的恒定(ding)(ding)電(dian)(dian)流(liu)。LTC1733將一(yi)直(zhi)保持恒流(liu)模(mo)式，直(zhi)到(dao)BAT腳的電(dian)(dian)壓接近所選擇(ze)的最終浮置電(dian)(dian)壓(SEL=0V時為 4.1V ，SEL=VCC時為4.2V)為止。此(ci)后(hou)，器件(jian)進(jin)入恒壓模(mo)式。

　　在恒(heng)壓(ya)模式下，LTC1733將(jiang)開始(shi)降低充電(dian)電(dian)流(liu)(liu)以保(bao)持(chi)BAT腳(jiao)的(de)恒(heng)壓(ya)而非恒(heng)流(liu)(liu)輸出。當電(dian)流(liu)(liu)降至最大(da)設定充電(dian)電(dian)流(liu)(liu)的(de)10%時，內部比較(jiao)器會斷開CHRG腳(jiao)，并(bing)將(jiang)一(yi)弱電(dian)流(liu)(liu)源(約25(A)接(jie)地，以顯示接(jie)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同，LTC1733在到(dao)達C/10點后，只(zhi)要(yao)終止(zhi)定(ding)時(shi)器時(shi)間不到(dao)，會(hui)繼(ji)續給電(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)電(dian)，以保證電(dian)池(chi)(chi)(chi)完全(quan)充(chong)(chong)(chong)滿。在C/10處終止(zhi)充(chong)(chong)(chong)電(dian)過程使(shi)(shi)電(dian)池(chi)(chi)(chi)只(zhi)能充(chong)(chong)(chong)到(dao)其(qi)容(rong)量的90%到(dao)95%，而在C/10后繼(ji)續充(chong)(chong)(chong)并按時(shi)間要(yao)求(qiu)結束(shu)可使(shi)(shi)電(dian)池(chi)(chi)(chi)的容(rong)量充(chong)(chong)(chong)到(dao)100%。一旦充(chong)(chong)(chong)電(dian)結束(shu)，CHRG腳(jiao)便呈現高(gao)阻抗(kang)狀態(tai)。

    電池的再充電
    假定(ding)在第一次充(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)，電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓已充(chong)到了3.95V(SEL = 0V時(shi)) 或(huo)4.05V (SEL = VCC時(shi))以(yi)上，那么LTC1733可對電(dian)(dian)(dian)(dian)(dian)池進行再充(chong)電(dian)(dian)(dian)(dian)(dian)。一旦超出這些閾值，如果電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓因電(dian)(dian)(dian)(dian)(dian)池負載的(de)存在或(huo)電(dian)(dian)(dian)(dian)(dian)池的(de)自放電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流而掉到3.9V (SEL = 0V)或(huo)4.0V (SEL = VCC)以(yi)下時(shi)，則新(xin)一輪(lun)的(de)充(chong)電(dian)(dian)(dian)(dian)(dian)循環(huan)開始了。再充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)路(lu)集結BAT腳電(dian)(dian)(dian)(dian)(dian)壓數毫秒，以(yi)防止(zhi)充(chong)電(dian)(dian)(dian)(dian)(dian)循環(huan)重啟造成的(de)瞬態沖擊。

    熱調節
　　LTC1733的另一個特性是(shi)具(ju)有內部熱(re)調節回路。如果高(gao)(gao)功率操作(zuo)或高(gao)(gao)的環境(jing)溫度(du)(du)(du)導致LTC1733的溫度(du)(du)(du)接近(jin)105(C，那么(me)充(chong)電(dian)電(dian)流(liu)會自動降低(di)以將(jiang)溫度(du)(du)(du)保持在(zai)105(C左右 (板(ban)溫度(du)(du)(du)通常低(di)于85(C)，這便是(shi)所謂的恒溫模式。這一特性允許(xu)用戶(hu)基(ji)于具(ju)體的工(gong)作(zuo)條件設(she)定充(chong)電(dian)電(dian)流(liu)，并(bing)去掉許(xu)多線性應用必(bi)需的復雜過熱(re)保護設(she)計。

　　LTC1733會自動監視(shi)最糟狀態，這一特(te)性(xing)除可保(bao)護LTC1733外，還能(neng)去除板(ban)上的(de)“熱(re)點(dian)”區，從而保(bao)護周邊元件(jian)。其它的(de)電(dian)(dian)池充(chong)電(dian)(dian)器(qi)，其熱(re)關(guan)(guan)閉特(te)性(xing)只是簡單地在極高溫(wen)度(du)(du)下(xia)(一般(ban)是150(C)關(guan)(guan)閉充(chong)電(dian)(dian)器(qi)而已。這種基于溫(wen)度(du)(du)的(de)關(guan)(guan)閉特(te)性(xing)允許電(dian)(dian)池充(chong)電(dian)(dian)器(qi)和(he)周邊PCB板(ban)溫(wen)度(du)(du)升至非常高，盡管具備關(guan)(guan)閉“保(bao)護”功能(neng)，但必須對應用(yong)進行仔細設計以避免到(dao)達(da)熱(re)關(guan)(guan)閉溫(wen)度(du)(du)。LTC1733通過自動均衡充(chong)電(dian)(dian)電(dian)(dian)流、散熱(re)和(he)工作溫(wen)度(du)(du)，可使設計得到(dao)簡化。

　　為進一步(bu)改(gai)進LTC1733的(de)熱調(diao)節(jie)性能，它采用(yong)了熱增(zeng)強型MSOP封裝。其占用(yong)板(ban)面積可做到小于72 mm2，室(shi)溫功(gong)耗2W。這(zhe)相當于用(yong)5V輸(shu)入電源實現(xian)最大(da)(da)充(chong)(chong)電電流(liu)1.5A。這(zhe)里假(jia)定(ding)鋰離(li)(li)子(zi)電池(chi)在充(chong)(chong)電大(da)(da)部分時間里處于(3.7V狀態。實際上(shang)，由于典型的(de)鋰離(li)(li)子(zi)電池(chi)在充(chong)(chong)電開(kai)始幾分鐘內便(bian)升到3.8V以上(shang)，因此這(zhe)一假(jia)定(ding)有些(xie)保守。LTC1733的(de)這(zhe)一獨特(te)(te)熱特(te)(te)性和7%的(de)設定(ding)充(chong)(chong)電電流(liu)精(jing)度(du)，使單電池(chi)鋰離(li)(li)子(zi)電池(chi)系統的(de)充(chong)(chong)電過程(cheng)非常迅速(su)和精(jing)確(que)。

　　PROG電流監控器
　　在恒流模式(shi)下，PROG腳的電(dian)壓總為1.5V，指示設定的充電(dian)電(dian)流從BAT腳流出(chu)(chu)。在恒溫或恒壓模式(shi)下，BAT腳的電(dian)流有所下降。PROG腳與三個(ge)開漏(lou)狀(zhuang)態輸出(chu)(chu)(ACPR、CHRG和 FAULT)時刻(ke)通告用戶(hu)LTC1733到底(di)在做什(shen)么。

　　NTC熱敏電阻
　　除了(le)可(ke)編程定時器(qi)(qi)(qi)和低的(de)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)限(xian)定條件(jian)外(wai)，LTC1733在(zai)推薦給電(dian)(dian)(dian)池(chi)制造商的(de)安全(quan)性特性列表中還增加了(le)充(chong)電(dian)(dian)(dian)時的(de)溫度(du)限(xian)定。電(dian)(dian)(dian)池(chi)溫度(du)通過緊貼電(dian)(dian)(dian)池(chi)組放置一(yi)只(zhi)負溫度(du)系(xi)數(NTC)熱(re)敏電(dian)(dian)(dian)阻(zu)(zu)來測(ce)定。借助IC中的(de)內(nei)部溫度(du)限(xian)制電(dian)(dian)(dian)路，LTC1733在(zai)電(dian)(dian)(dian)池(chi)溫度(du)降到0(C以下(xia)或升到50(C以上時，可(ke)臨時停(ting)住內(nei)部定時器(qi)(qi)(qi)并停(ting)止充(chong)電(dian)(dian)(dian)。實施這(zhe)一(yi)功能，選用(yong)RHOT的(de)電(dian)(dian)(dian)阻(zu)(zu)值應(ying)與(yu)50(C下(xia)所用(yong)熱(re)敏電(dian)(dian)(dian)阻(zu)(zu)的(de)阻(zu)(zu)值相同。這(zhe)樣將可(ke)以確保內(nei)部比較器(qi)(qi)(qi)的(de)1/2VCC摔(shuai)點(trip point)與(yu)NTC的(de)50(C溫度(du)相對(dui)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 性能(neng)概要(yao)：