便攜式電(dian)(dian)源(yuan)的(de)(de)應用范(fan)圍很(hen)廣，也很(hen)多樣化。產品包括消耗(hao)uW級(ji)平均功(gong)(gong)率的(de)(de)無線(xian)傳(chuan)感器節點以及可(ke)用小(xiao)車推著的(de)(de)、電(dian)(dian)池(chi)組耗(hao)電(dian)(dian)數百瓦-時(shi)的(de)(de)醫(yi)療或數據采(cai)集系(xi)統。不過，盡管應用種類很(hen)多，仍然(ran)出現了(le)幾個趨勢，設計(ji)師日(ri)益需要給產品提(ti)(ti)供更大(da)(da)的(de)(de)功(gong)(gong)率，以支(zhi)持不斷增多的(de)(de)功(gong)(gong)能，同時(shi)也在考慮怎(zen)樣用任(ren)何可(ke)用電(dian)(dian)源(yuan)給電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)。要滿(man)足第一種需求(qiu)(qiu)，就(jiu)要提(ti)(ti)高(gao)電(dian)(dian)池(chi)容量(liang)。不幸的(de)(de)是(shi)，用戶大(da)(da)多比(bi)較心(xin)急(ji)，容量(liang)提(ti)(ti)高(gao)以后，還必須在一個合理的(de)(de)時(shi)間(jian)內充(chong)(chong)滿(man)電(dian)(dian)，這(zhe)就(jiu)導致(zhi)要增大(da)(da)充(chong)(chong)電(dian)(dian)電(dian)(dian)流。要滿(man)足第二種需求(qiu)(qiu)，就(jiu)要求(qiu)(qiu)電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)解決方(fang)案提(ti)(ti)供極大(da)(da)的(de)(de)靈(ling)活性。本文將更詳細地(di)討(tao)論這(zhe)些問題。

　　更大的功率

　　考慮一(yi)下(xia)新式手(shou)持式設(she)備，面(mian)向(xiang)消費者的(de)(de)(de)設(she)備和(he)工業設(she)備都(dou)(dou)可能包(bao)括(kuo)蜂(feng)窩(wo)電(dian)(dian)話調制解調器(qi)、Wi-Fi模塊(kuai)、藍牙模塊(kuai)、大尺寸背光(guang)照明(ming)(ming)顯示(shi)屏…等(deng)等(deng)。很(hen)(hen)多手(shou)持式設(she)備的(de)(de)(de)電(dian)(dian)源(yuan)架構(gou)(gou)都(dou)(dou)與蜂(feng)窩(wo)電(dian)(dian)話的(de)(de)(de)非常相似(si)。一(yi)般情況下(xia)，用(yong)(yong)(yong)一(yi)個(ge)3.7V的(de)(de)(de)鋰(li)(li)離子電(dian)(dian)池作為(wei)主電(dian)(dian)源(yuan)，因為(wei)鋰(li)(li)離子電(dian)(dian)池按重量和(he)按體積的(de)(de)(de)能量密度都(dou)(dou)很(hen)(hen)高(單位分(fen)別(bie)為(wei)Wh/kg和(he)Wh/m3)。過去，很(hen)(hen)多大功率設(she)備都(dou)(dou)采(cai)用(yong)(yong)(yong)7.4V鋰(li)(li)離子電(dian)(dian)池，以降低電(dian)(dian)流要求，不(bu)過低價5V電(dian)(dian)源(yuan)管理IC的(de)(de)(de)上市已經促使越來越多的(de)(de)(de)手(shou)持式設(she)備采(cai)用(yong)(yong)(yong)了電(dian)(dian)壓更低的(de)(de)(de)架構(gou)(gou)。平(ping)板電(dian)(dian)腦很(hen)(hen)好地說明(ming)(ming)了這一(yi)點：一(yi)個(ge)典(dian)型的(de)(de)(de)平(ping)板電(dian)(dian)腦有極多的(de)(de)(de)功能以及非常大的(de)(de)(de)顯示(shi)屏(就便攜式設(she)備而言)。用(yong)(yong)(yong)3.7V電(dian)(dian)池供(gong)電(dian)(dian)時(shi)，其容(rong)量必須以數千毫安-小時(shi)計算(suan)。為(wei)了在(zai)幾(ji)個(ge)小時(shi)內給這樣一(yi)個(ge)電(dian)(dian)池充(chong)滿電(dian)(dian)，需要數千mA的(de)(de)(de)充(chong)電(dian)(dian)電(dian)(dian)流。

　　然而(er)，如果沒有(you)大(da)電(dian)流(liu)交流(liu)適(shi)配(pei)(pei)器，盡(jin)管充(chong)電(dian)電(dian)流(liu)這么高(gao)，也不能(neng)(neng)防止消費(fei)者用(yong)(yong)USB端口給大(da)功(gong)率(lv)設備充(chong)電(dian)的想(xiang)法。為(wei)了滿足這種需(xu)求(qiu)，當交流(liu)適(shi)配(pei)(pei)器可用(yong)(yong)時(shi)，電(dian)池(chi)(chi)充(chong)電(dian)器必(bi)須能(neng)(neng)以大(da)電(dian)流(liu)(>2A)充(chong)電(dian)，而(er)在沒有(you)交流(liu)適(shi)配(pei)(pei)器可用(yong)(yong)時(shi)，電(dian)池(chi)(chi)充(chong)電(dian)器必(bi)須仍(reng)能(neng)(neng)高(gao)效地(di)利用(yong)(yong)USB端口提供2.5W至4.5W功(gong)率(lv)。此外(wai)，器件(jian)必(bi)須保護敏感的下(xia)游低壓組件(jian)免受可能(neng)(neng)出現過壓情況所(suo)導(dao)致的損(sun)壞，同時(shi)必(bi)須無縫地(di)將大(da)電(dian)流(liu)從USB輸(shu)入、交流(liu)適(shi)配(pei)(pei)器或電(dian)池(chi)(chi)傳送(song)到負載，并最(zui)大(da)限(xian)度地(di)降(jiang)低功(gong)耗。另外(wai)，該IC還必(bi)須安全(quan)地(di)管理電(dian)池(chi)(chi)充(chong)電(dian)算法，并監視關(guan)鍵的系統參數。

　　戰(zhan)(zhan)勝單節電池供電的(de)便攜式產(chan)品在(zai)功率方面的(de)挑(tiao)戰(zhan)(zhan)

　　盡(jin)管(guan)看似不可(ke)能找到能滿足上述要求的(de)單個(ge)IC，不過看一下LTC4155，這是一個(ge)大功(gong)率、I2C控制(zhi)的(de)高效(xiao)率電(dian)源(yuan)通路(lu)(PowerPath?)管(guan)理器(qi)、理想二極管(guan)控制(zhi)器(qi)和鋰(li)離(li)子(zi)電(dian)池(chi)(chi)充電(dian)器(qi)。該IC用來從各種(zhong)5V電(dian)源(yuan)高效(xiao)地傳送高達3A的(de)電(dian)流，可(ke)產生超(chao)過3.5A的(de)可(ke)用電(dian)流，以供(gong)電(dian)池(chi)(chi)充電(dian)和系(xi)統使用(參見圖(tu)1)。LTC4155的(de)效(xiao)率為88%至94%，因此即使電(dian)流值這么(me)大，該IC仍(reng)然可(ke)以減輕熱(re)量預算限制(zhi)(參見圖(tu)2)。LTC4155的(de)開關式(shi)電(dian)源(yuan)通路(lu)拓撲無縫地管(guan)理從兩種(zhong)輸入電(dian)源(yuan)(例如一個(ge)交流適配器(qi)和一個(ge)USB端(duan)口)到設(she)備中可(ke)再(zai)充電(dian)鋰(li)離(li)子(zi)電(dian)池(chi)(chi)的(de)配電(dian)，同時當輸入功(gong)率有限時，優先(xian)為系(xi)統負(fu)載供(gong)電(dian)。

圖1：LTC4155的典(dian)型(xing)應用電(dian)路(lu)

圖2：LTC4155的典型效率(lv)

　　與典型的(de)線性模(mo)式充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)相比(bi)，LTC4155中(zhong)開(kai)關穩壓器(qi)(qi)的(de)作用就像一個變壓器(qi)(qi)，允許(xu)VOUT上的(de)負(fu)載(zai)電(dian)(dian)(dian)(dian)流超過輸入電(dian)(dian)(dian)(dian)源吸取的(de)電(dian)(dian)(dian)(dian)流，并極大地(di)提高(gao)電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)可用功率。前述(shu)例子說(shuo)明了LTC4155怎樣才能以高(gao)達(da)3.5A的(de)電(dian)(dian)(dian)(dian)流高(gao)效率地(di)充(chong)(chong)電(dian)(dian)(dian)(dian)，以實(shi)現更快的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)時間。與普(pu)通的(de)開(kai)關型電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)不同，LTC4155可即(ji)時接通工作，以確保(bao)即(ji)使電(dian)(dian)(dian)(dian)池(chi)沒(mei)電(dian)(dian)(dian)(dian)或(huo)已深(shen)度放電(dian)(dian)(dian)(dian)，當(dang)一插上電(dian)(dian)(dian)(dian)源插頭，系統電(dian)(dian)(dian)(dian)源也立即(ji)可用。

　　盡管是(shi)以很高(gao)的(de)(de)速率(lv)給電池充(chong)電，監視(shi)電池是(shi)否安全也是(shi)很重要的(de)(de)。當電池溫(wen)(wen)度降(jiang)至低(di)于(yu)0°C或升至高(gao)于(yu)40°C[由一個(ge)(ge)外部負溫(wen)(wen)度系數(NTC)熱(re)敏電阻測量]時，LTC4155將自動停(ting)止充(chong)電。除了這(zhe)種自主(zhu)式功能，LTC4155還提供一個(ge)(ge)7位擴展標度模數轉換器(qi)(ADC)，以大約1°C的(de)(de)分辨率(lv)監視(shi)電池溫(wen)(wen)度(參見圖3)。結(jie)合4個(ge)(ge)可用的(de)(de)浮置電壓(ya)設定值和15個(ge)(ge)電池充(chong)電電流(liu)設定值，該ADC可基于(yu)電池溫(wen)(wen)度來建立定制的(de)(de)充(chong)電算法。

圖3：7位熱敏電阻器ADC顯示LTC4155的預置(zhi)溫度(du)跳變點

　　通過一個簡單的兩線I2C端口可獲得NTCADC的結果，從而能調節充電電流和電壓的設定值。該I2C端口通過控制16個輸入電流的設定值(包括USB2.0和3.0兼容設置)，還可提供USB兼容性。該通信總線允許LTC4155指示額外的狀態信息，例如輸入電源狀態、充電器狀(zhuang)態和故障狀(zhuang)態。由于支持USBOTG，因此無需任何額(e)外的(de)組件，就可以反過來向(xiang)USB端口提(ti)供5V電源(yuan)。

　　LTC4155的(de)(de)雙路(lu)(lu)輸(shu)(shu)入(ru)(ru)、優先(xian)級多路(lu)(lu)復(fu)用(yong)器(qi)(qi)可根據用(yong)戶定義的(de)(de)優先(xian)級(默認的(de)(de)優先(xian)級為適配器(qi)(qi)輸(shu)(shu)入(ru)(ru))自主地選擇最合適的(de)(de)輸(shu)(shu)入(ru)(ru)(即(ji)墻上適配器(qi)(qi)或USB)。過壓(ya)保護(OVP)電路(lu)(lu)同時保護兩個輸(shu)(shu)入(ru)(ru)，以免這些輸(shu)(shu)入(ru)(ru)因無意間(jian)加上的(de)(de)高(gao)壓(ya)或反向電壓(ya)而損壞(huai)。LTC4155的(de)(de)理想二極(ji)管控制器(qi)(qi)保證即(ji)使輸(shu)(shu)入(ru)(ru)功率不足或未提(ti)供(gong)輸(shu)(shu)入(ru)(ru)功率時，也始終可向VOUT提(ti)供(gong)足夠的(de)(de)功率。

　　就平板電(dian)腦、工(gong)業條碼掃(sao)描(miao)器(qi)(qi)等很多便攜(xie)式應用(yong)而言，能管(guan)理兩個輸入(ru)(例如(ru)USB和(he)交(jiao)流適配器(qi)(qi))就足夠(gou)了。不過，便攜(xie)式設備的設計師一(yi)直在(zai)尋(xun)求用(yong)任何可用(yong)電(dian)源都能給電(dian)池充電(dian)的方法

　　多種輸入源

　　用(yong)(yong)(yong)(yong)(yong)戶要用(yong)(yong)(yong)(yong)(yong)多(duo)種(zhong)輸(shu)(shu)入(ru)(ru)源(yuan)給(gei)電(dian)(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)有幾個(ge)原因。有些應用(yong)(yong)(yong)(yong)(yong)也許需要擺脫電(dian)(dian)(dian)(dian)網的(de)(de)束縛，而靠太陽(yang)能(neng)(neng)電(dian)(dian)(dian)(dian)池板(ban)供(gong)電(dian)(dian)(dian)(dian)。另一(yi)(yi)(yi)些應用(yong)(yong)(yong)(yong)(yong)則(ze)可能(neng)(neng)要求能(neng)(neng)方便(bian)地用(yong)(yong)(yong)(yong)(yong)交流適配器(qi)、汽車電(dian)(dian)(dian)(dian)池或(huo)(huo)高壓(ya)工(gong)業及電(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)源(yuan)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)。無(wu)論出于何種(zhong)原因，這(zhe)要求都給(gei)電(dian)(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)系統(tong)增加了極(ji)大(da)的(de)(de)負擔(dan)。大(da)多(duo)數電(dian)(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)都利(li)用(yong)(yong)(yong)(yong)(yong)降壓(ya)型(xing)(開關或(huo)(huo)線(xian)性)架(jia)構(gou)，用(yong)(yong)(yong)(yong)(yong)高于電(dian)(dian)(dian)(dian)池最高電(dian)(dian)(dian)(dian)壓(ya)的(de)(de)電(dian)(dian)(dian)(dian)壓(ya)源(yuan)給(gei)電(dian)(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)。以(yi)前的(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)產品(pin)輸(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)壓(ya)一(yi)(yi)(yi)般限(xian)制(zhi)為大(da)約30V。這(zhe)樣(yang)的(de)(de)限(xian)制(zhi)使(shi)設(she)計師無(wu)法將電(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)源(yuan)或(huo)(huo)者(zhe)具42V開路電(dian)(dian)(dian)(dian)壓(ya)的(de)(de)太陽(yang)能(neng)(neng)電(dian)(dian)(dian)(dian)池板(ban)作為可行的(de)(de)輸(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)源(yuan)。在(zai)有些情況下(xia)，希望(wang)使(shi)用(yong)(yong)(yong)(yong)(yong)的(de)(de)輸(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)壓(ya)涵蓋了高于和低于電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)的(de)(de)范(fan)圍(wei)。設(she)計一(yi)(yi)(yi)款應對此類難(nan)題的(de)(de)解決方案通常(chang)需要混合使(shi)用(yong)(yong)(yong)(yong)(yong)高精(jing)度的(de)(de)電(dian)(dian)(dian)(dian)流檢測放大(da)器(qi)、ADC、一(yi)(yi)(yi)個(ge)用(yong)(yong)(yong)(yong)(yong)于控制(zhi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)的(de)(de)微(wei)處理(li)器(qi)、一(yi)(yi)(yi)個(ge)高性能(neng)(neng)DC/DC轉換器(qi)以(yi)及一(yi)(yi)(yi)個(ge)理(li)想二極(ji)管或(huo)(huo)多(duo)路復用(yong)(yong)(yong)(yong)(yong)電(dian)(dian)(dian)(dian)路。

　　強大的(de)充(chong)電解決方案(an)提供無與倫比(bi)的(de)靈活(huo)性

　　LTC4000可將任何外部補償的DC/DC電源轉換成具電源通路(PowerPath?)控制的全功能電池充電器。可由LTC4000驅動的典型DC/DC轉換器拓撲包括但不限于：降壓、升壓、降壓-升壓、SEPIC和反激式拓撲。該器件提供精確的輸入和充電電流調節，在3V至60V的寬輸入和輸出電壓范圍內工作，實現了與各種不同的輸入電壓源、以及不同尺寸和化學組成的電池組的兼容性。由于該器件的通用型配置，因此其典型應用十分廣泛，包括高功率電池充電器系統、高(gao)性能(neng)便攜式儀器、電池后備系統、配有工業電池的設備以及筆記本/小型筆記本電腦。

　　除了可(ke)以與很多不同的DC/DC拓撲結合(he)，LTC4000的高壓能(neng)力(li)還允許該(gai)器(qi)件構(gou)成強大和幾乎可(ke)使(shi)(shi)用(yong)(yong)任何(he)輸入電(dian)(dian)(dian)源(參(can)見圖(tu)4和圖(tu)5)的電(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)解決方案。為了確保來自這些輸入的功(gong)率(lv)(lv)傳送(song)給合(he)適的負(fu)載，LTC4000采用(yong)(yong)了一(yi)種(zhong)智能(neng)電(dian)(dian)(dian)源通(tong)路拓撲，當(dang)輸入功(gong)率(lv)(lv)有限時，該(gai)拓撲可(ke)優先為系統(tong)負(fu)載供(gong)電(dian)(dian)(dian)。LTC4000控制外(wai)部(bu)PFET，以提供(gong)低損耗反向電(dian)(dian)(dian)流保護、電(dian)(dian)(dian)池(chi)(chi)的低損耗充(chong)電(dian)(dian)(dian)和放(fang)電(dian)(dian)(dian)以及即時接通(tong)工(gong)作，這樣就可(ke)以確保即使(shi)(shi)在(zai)電(dian)(dian)(dian)池(chi)(chi)沒電(dian)(dian)(dian)或(huo)深(shen)度放(fang)電(dian)(dian)(dian)時，當(dang)一(yi)插上電(dian)(dian)(dian)源，系統(tong)電(dian)(dian)(dian)源就能(neng)立即可(ke)用(yong)(yong)。外(wai)部(bu)檢測電(dian)(dian)(dian)阻器(qi)提供(gong)輸入電(dian)(dian)(dian)流和電(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流信息，從而使(shi)(shi)LTC4000能(neng)與涵蓋mW至(zhi)kW功(gong)率(lv)(lv)范圍的轉換器(qi)一(yi)起(qi)使(shi)(shi)用(yong)(yong)。

圖4：LTC4000和LTC3789：6V至36V_IN、4節5A鋰離子電(dian)池充(chong)電(dian)器

圖5：圖4電路中系(xi)統(tong)負載為4A時效率(lv)隨VIN的變化

　　LTC4000的全功能電池充電控制器可為各種化學組成的電池充電，包括鋰離子/聚合物/磷酸、密封鉛酸(SLA)和鎳化學組成。該電池充電器還提供精確(que)的電流檢測功能(neng)，從而在(zai)大(da)電流應用(yong)情況下(xia)允許較低的檢測電壓。

　　結論

　　新式便攜式產(chan)品(pin)設計師的工作(zuo)極(ji)富挑(tiao)戰性(xing)，尤其(qi)是涉及(ji)到電(dian)(dian)(dian)源時。客戶(hu)不(bu)斷要求更多(duo)功(gong)能(neng)以導致(zhi)需要更大(da)的功(gong)率(lv)，結果(guo)是電(dian)(dian)(dian)池越來(lai)越大(da)。同時，客戶(hu)希望可(ke)(ke)方便地用幾乎任(ren)何可(ke)(ke)用的電(dian)(dian)(dian)源給這些電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)。盡管便攜式電(dian)(dian)(dian)源領(ling)域的這些趨勢(shi)造成了設計挑(tiao)戰，但是LTC4155和(he)LTC4000讓設計工作(zuo)變得簡單多(duo)了。在低壓系統中，LTC4155高(gao)效率(lv)地提供高(gao)達3.5A的充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流，而且提供很(hen)多(duo)高(gao)性(xing)能(neng)功(gong)能(neng)。LTC4000可(ke)(ke)構成強大(da)的充(chong)電(dian)(dian)(dian)解(jie)決方案，而且幾乎可(ke)(ke)使(shi)用任(ren)何輸入，從(cong)而提供了無與倫比(bi)的性(xing)能(neng)和(he)靈活性(xing)。