便攜式電(dian)(dian)源(yuan)的(de)(de)(de)應用(yong)范圍很廣，也很多樣化。產品包括(kuo)消耗uW級平均功率(lv)的(de)(de)(de)無線傳感器節點以(yi)及可用(yong)小車(che)推著(zhu)的(de)(de)(de)、電(dian)(dian)池組耗電(dian)(dian)數百瓦-時的(de)(de)(de)醫療(liao)或(huo)數據采集(ji)系統。不過，盡管應用(yong)種類很多，仍(reng)然出現了(le)幾個(ge)趨勢(shi)，設計師日益需(xu)要給產品提(ti)供(gong)更大的(de)(de)(de)功率(lv)，以(yi)支持不斷增多的(de)(de)(de)功能，同時也在(zai)(zai)考慮怎樣用(yong)任何可用(yong)電(dian)(dian)源(yuan)給電(dian)(dian)池充(chong)電(dian)(dian)。要滿(man)足第一種需(xu)求(qiu)，就(jiu)要提(ti)高電(dian)(dian)池容量(liang)。不幸(xing)的(de)(de)(de)是，用(yong)戶大多比較心(xin)急(ji)，容量(liang)提(ti)高以(yi)后，還必須在(zai)(zai)一個(ge)合理的(de)(de)(de)時間內充(chong)滿(man)電(dian)(dian)，這(zhe)就(jiu)導致要增大充(chong)電(dian)(dian)電(dian)(dian)流。要滿(man)足第二種需(xu)求(qiu)，就(jiu)要求(qiu)電(dian)(dian)池充(chong)電(dian)(dian)解決方案提(ti)供(gong)極(ji)大的(de)(de)(de)靈活性。本(ben)文(wen)將更詳細地討論這(zhe)些問題(ti)。

　　更大的功率

　　考(kao)慮一下(xia)新式手(shou)持(chi)式設(she)(she)備(bei)，面向消費者的(de)設(she)(she)備(bei)和工業設(she)(she)備(bei)都(dou)(dou)可能(neng)(neng)包括蜂窩(wo)(wo)電(dian)(dian)(dian)(dian)(dian)話調(diao)制解調(diao)器、Wi-Fi模塊、藍牙模塊、大(da)尺寸(cun)背(bei)光照明顯(xian)示屏(ping)…等等。很(hen)(hen)(hen)多(duo)手(shou)持(chi)式設(she)(she)備(bei)的(de)電(dian)(dian)(dian)(dian)(dian)源(yuan)架構都(dou)(dou)與蜂窩(wo)(wo)電(dian)(dian)(dian)(dian)(dian)話的(de)非常相似。一般情況下(xia)，用(yong)一個(ge)(ge)3.7V的(de)鋰(li)離(li)子電(dian)(dian)(dian)(dian)(dian)池作為(wei)(wei)主電(dian)(dian)(dian)(dian)(dian)源(yuan)，因為(wei)(wei)鋰(li)離(li)子電(dian)(dian)(dian)(dian)(dian)池按(an)重量和按(an)體(ti)積的(de)能(neng)(neng)量密(mi)度都(dou)(dou)很(hen)(hen)(hen)高(gao)(單位分別為(wei)(wei)Wh/kg和Wh/m3)。過去，很(hen)(hen)(hen)多(duo)大(da)功率設(she)(she)備(bei)都(dou)(dou)采用(yong)7.4V鋰(li)離(li)子電(dian)(dian)(dian)(dian)(dian)池，以(yi)降(jiang)低(di)(di)電(dian)(dian)(dian)(dian)(dian)流要求(qiu)，不(bu)過低(di)(di)價5V電(dian)(dian)(dian)(dian)(dian)源(yuan)管(guan)理IC的(de)上(shang)市已經促使(shi)越來越多(duo)的(de)手(shou)持(chi)式設(she)(she)備(bei)采用(yong)了電(dian)(dian)(dian)(dian)(dian)壓更低(di)(di)的(de)架構。平板(ban)電(dian)(dian)(dian)(dian)(dian)腦(nao)很(hen)(hen)(hen)好(hao)地說明了這一點：一個(ge)(ge)典型的(de)平板(ban)電(dian)(dian)(dian)(dian)(dian)腦(nao)有極多(duo)的(de)功能(neng)(neng)以(yi)及非常大(da)的(de)顯(xian)示屏(ping)(就(jiu)便攜式設(she)(she)備(bei)而(er)言(yan))。用(yong)3.7V電(dian)(dian)(dian)(dian)(dian)池供(gong)電(dian)(dian)(dian)(dian)(dian)時，其容量必須以(yi)數(shu)千毫安-小時計算。為(wei)(wei)了在幾個(ge)(ge)小時內給(gei)這樣(yang)一個(ge)(ge)電(dian)(dian)(dian)(dian)(dian)池充滿電(dian)(dian)(dian)(dian)(dian)，需要數(shu)千mA的(de)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流。

　　然而，如果沒有大(da)電(dian)(dian)(dian)(dian)流(liu)交流(liu)適(shi)(shi)配器(qi)(qi)，盡管充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)這么高，也(ye)不能(neng)防止消費(fei)者用(yong)USB端口(kou)給大(da)功(gong)率(lv)設備充(chong)電(dian)(dian)(dian)(dian)的想法。為了滿足這種(zhong)需求，當交流(liu)適(shi)(shi)配器(qi)(qi)可(ke)用(yong)時(shi)，電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)必(bi)須能(neng)以大(da)電(dian)(dian)(dian)(dian)流(liu)(>2A)充(chong)電(dian)(dian)(dian)(dian)，而在沒有交流(liu)適(shi)(shi)配器(qi)(qi)可(ke)用(yong)時(shi)，電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)必(bi)須仍能(neng)高效地(di)利用(yong)USB端口(kou)提供(gong)2.5W至(zhi)4.5W功(gong)率(lv)。此(ci)外(wai)，器(qi)(qi)件(jian)必(bi)須保護敏感的下游(you)低壓(ya)組件(jian)免受可(ke)能(neng)出現過(guo)壓(ya)情況所導(dao)致(zhi)的損(sun)壞(huai)，同時(shi)必(bi)須無(wu)縫地(di)將(jiang)大(da)電(dian)(dian)(dian)(dian)流(liu)從(cong)USB輸(shu)入(ru)、交流(liu)適(shi)(shi)配器(qi)(qi)或電(dian)(dian)(dian)(dian)池傳送到(dao)負載，并最大(da)限度地(di)降低功(gong)耗。另外(wai)，該IC還必(bi)須安全地(di)管理電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)算法，并監視關(guan)鍵的系統參數。

　　戰勝單節電池供電的便攜式(shi)產(chan)品(pin)在功率方面的挑戰

　　盡(jin)管(guan)看似不可(ke)(ke)能找到(dao)能滿足上述(shu)要求的(de)(de)單(dan)個(ge)IC，不過(guo)(guo)看一下LTC4155，這是一個(ge)大(da)功(gong)率、I2C控(kong)制的(de)(de)高效率電(dian)(dian)源(yuan)通路(PowerPath?)管(guan)理器(qi)、理想二極管(guan)控(kong)制器(qi)和(he)鋰(li)離子電(dian)(dian)池充電(dian)(dian)器(qi)。該IC用來(lai)從(cong)各種(zhong)5V電(dian)(dian)源(yuan)高效地傳送高達(da)3A的(de)(de)電(dian)(dian)流(liu)(liu)，可(ke)(ke)產生超過(guo)(guo)3.5A的(de)(de)可(ke)(ke)用電(dian)(dian)流(liu)(liu)，以(yi)供(gong)電(dian)(dian)池充電(dian)(dian)和(he)系統使用(參見(jian)圖(tu)1)。LTC4155的(de)(de)效率為88%至94%，因此即使電(dian)(dian)流(liu)(liu)值(zhi)這么大(da)，該IC仍(reng)然可(ke)(ke)以(yi)減輕熱量預算(suan)限(xian)制(參見(jian)圖(tu)2)。LTC4155的(de)(de)開關式電(dian)(dian)源(yuan)通路拓撲無縫地管(guan)理從(cong)兩種(zhong)輸入電(dian)(dian)源(yuan)(例如一個(ge)交流(liu)(liu)適配器(qi)和(he)一個(ge)USB端(duan)口)到(dao)設備中可(ke)(ke)再充電(dian)(dian)鋰(li)離子電(dian)(dian)池的(de)(de)配電(dian)(dian)，同時(shi)當輸入功(gong)率有(you)限(xian)時(shi)，優先為系統負載(zai)供(gong)電(dian)(dian)。

圖1：LTC4155的典型(xing)應用電路

圖(tu)2：LTC4155的典(dian)型效率

　　與(yu)典型(xing)的(de)(de)線性模式充(chong)電(dian)(dian)(dian)(dian)(dian)器相(xiang)比，LTC4155中開關穩(wen)壓器的(de)(de)作用(yong)就像一個(ge)變壓器，允許(xu)VOUT上(shang)(shang)的(de)(de)負(fu)載電(dian)(dian)(dian)(dian)(dian)流超過輸入(ru)電(dian)(dian)(dian)(dian)(dian)源(yuan)吸取的(de)(de)電(dian)(dian)(dian)(dian)(dian)流，并極大地(di)提高(gao)電(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)的(de)(de)可(ke)(ke)(ke)用(yong)功率(lv)。前述例子(zi)說明了LTC4155怎樣才能以高(gao)達3.5A的(de)(de)電(dian)(dian)(dian)(dian)(dian)流高(gao)效率(lv)地(di)充(chong)電(dian)(dian)(dian)(dian)(dian)，以實現(xian)更(geng)快的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)時間(jian)。與(yu)普通(tong)的(de)(de)開關型(xing)電(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)器不同(tong)，LTC4155可(ke)(ke)(ke)即(ji)(ji)時接通(tong)工作，以確保(bao)即(ji)(ji)使電(dian)(dian)(dian)(dian)(dian)池沒(mei)電(dian)(dian)(dian)(dian)(dian)或已深度放電(dian)(dian)(dian)(dian)(dian)，當(dang)一插(cha)上(shang)(shang)電(dian)(dian)(dian)(dian)(dian)源(yuan)插(cha)頭，系統電(dian)(dian)(dian)(dian)(dian)源(yuan)也(ye)立即(ji)(ji)可(ke)(ke)(ke)用(yong)。

　　盡管(guan)是(shi)以很高的(de)速率給電(dian)(dian)池(chi)充電(dian)(dian)，監視電(dian)(dian)池(chi)是(shi)否(fou)安(an)全也是(shi)很重要的(de)。當電(dian)(dian)池(chi)溫度(du)降至低于0°C或升至高于40°C[由一個(ge)(ge)外部負溫度(du)系數(NTC)熱(re)敏電(dian)(dian)阻測量]時(shi)，LTC4155將(jiang)自(zi)動(dong)停止充電(dian)(dian)。除了這(zhe)種(zhong)自(zi)主式功能，LTC4155還提(ti)供一個(ge)(ge)7位擴展標(biao)度(du)模數轉換器(ADC)，以大約1°C的(de)分(fen)辨率監視電(dian)(dian)池(chi)溫度(du)(參見圖3)。結合4個(ge)(ge)可(ke)用的(de)浮置電(dian)(dian)壓設定值和15個(ge)(ge)電(dian)(dian)池(chi)充電(dian)(dian)電(dian)(dian)流設定值，該ADC可(ke)基于電(dian)(dian)池(chi)溫度(du)來建(jian)立(li)定制的(de)充電(dian)(dian)算法。

圖3：7位熱敏電阻器ADC顯(xian)示(shi)LTC4155的(de)預置(zhi)溫度跳(tiao)變(bian)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)(zhuang)態(tai)和故障狀(zhuang)(zhuang)態(tai)。由于支持(chi)USBOTG，因(yin)此無需(xu)任何額外(wai)的(de)組件，就可以反(fan)過來向USB端(duan)口提供5V電(dian)源(yuan)。

　　LTC4155的(de)雙路(lu)輸入(ru)、優先級(ji)(ji)多(duo)路(lu)復(fu)用器(qi)可(ke)根據用戶定義的(de)優先級(ji)(ji)(默認的(de)優先級(ji)(ji)為適配器(qi)輸入(ru))自主(zhu)地選(xuan)擇最合適的(de)輸入(ru)(即墻上(shang)適配器(qi)或USB)。過壓保護(hu)(hu)(OVP)電(dian)路(lu)同時保護(hu)(hu)兩個輸入(ru)，以免這(zhe)些(xie)輸入(ru)因(yin)無意間加(jia)上(shang)的(de)高壓或反向(xiang)電(dian)壓而損壞。LTC4155的(de)理(li)想(xiang)二極管控制器(qi)保證(zheng)即使輸入(ru)功率(lv)不足(zu)或未提供(gong)輸入(ru)功率(lv)時，也始(shi)終(zhong)可(ke)向(xiang)VOUT提供(gong)足(zu)夠的(de)功率(lv)。

　　就(jiu)平板電腦、工業條碼掃描器等很多便攜式應用(yong)而(er)言(yan)，能(neng)管理兩(liang)個輸入(ru)(例(li)如(ru)USB和交流適配(pei)器)就(jiu)足夠了。不過，便攜式設備的(de)設計(ji)師(shi)一直在尋(xun)求用(yong)任何可用(yong)電源(yuan)都能(neng)給電池充電的(de)方法

　　多種輸入源

　　用(yong)戶要(yao)(yao)(yao)用(yong)多種(zhong)輸(shu)入源(yuan)給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)有幾個(ge)原(yuan)(yuan)因(yin)。有些應(ying)用(yong)也許(xu)需要(yao)(yao)(yao)擺脫電(dian)(dian)(dian)(dian)(dian)(dian)網的(de)(de)(de)束(shu)縛(fu)，而靠太陽(yang)能電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)板供電(dian)(dian)(dian)(dian)(dian)(dian)。另(ling)一(yi)些應(ying)用(yong)則(ze)可能要(yao)(yao)(yao)求(qiu)能方便(bian)地用(yong)交流(liu)適(shi)配器(qi)、汽車電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)或(huo)高(gao)(gao)壓工業及電(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。無論出(chu)于何(he)種(zhong)原(yuan)(yuan)因(yin)，這要(yao)(yao)(yao)求(qiu)都給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)系(xi)統增(zeng)加了(le)極(ji)大(da)的(de)(de)(de)負擔。大(da)多數電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)都利用(yong)降壓型(開(kai)關或(huo)線性)架(jia)構，用(yong)高(gao)(gao)于電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)最高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓源(yuan)給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。以前(qian)的(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)產品輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)壓一(yi)般限制為大(da)約30V。這樣(yang)的(de)(de)(de)限制使設計師無法將電(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)或(huo)者具42V開(kai)路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)(de)(de)太陽(yang)能電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)板作為可行的(de)(de)(de)輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)。在有些情(qing)況下，希望(wang)使用(yong)的(de)(de)(de)輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)壓涵蓋了(le)高(gao)(gao)于和低于電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)(de)(de)范圍。設計一(yi)款應(ying)對此類難題(ti)的(de)(de)(de)解決方案(an)通常需要(yao)(yao)(yao)混(hun)合使用(yong)高(gao)(gao)精度的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)檢測放大(da)器(qi)、ADC、一(yi)個(ge)用(yong)于控制充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)微(wei)處(chu)理器(qi)、一(yi)個(ge)高(gao)(gao)性能DC/DC轉換器(qi)以及一(yi)個(ge)理想二極(ji)管或(huo)多路(lu)復用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。

　　強大的充(chong)電解決方(fang)案提供(gong)無與倫比的靈活性

　　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(xi)統(tong)、高(gao)性能便攜式儀器、電池(chi)(chi)后備系(xi)統(tong)、配有工業電池(chi)(chi)的設備以及(ji)筆記本/小型筆記本電腦。

　　除了(le)可(ke)(ke)以(yi)(yi)與(yu)很多不同的(de)(de)(de)DC/DC拓撲結合(he)，LTC4000的(de)(de)(de)高壓能力(li)還允許該(gai)器件(jian)構成強(qiang)大和幾乎可(ke)(ke)使(shi)用任何(he)輸(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)源(參見圖4和圖5)的(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)解決(jue)方案。為(wei)了(le)確保來自這些輸(shu)(shu)入(ru)(ru)的(de)(de)(de)功(gong)率傳(chuan)送給合(he)適的(de)(de)(de)負載(zai)，LTC4000采用了(le)一種智能電(dian)(dian)(dian)(dian)源通路拓撲，當輸(shu)(shu)入(ru)(ru)功(gong)率有限時(shi)，該(gai)拓撲可(ke)(ke)優先為(wei)系(xi)統負載(zai)供電(dian)(dian)(dian)(dian)。LTC4000控制(zhi)外部(bu)PFET，以(yi)(yi)提供低損耗反向電(dian)(dian)(dian)(dian)流保護、電(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)低損耗充電(dian)(dian)(dian)(dian)和放電(dian)(dian)(dian)(dian)以(yi)(yi)及即(ji)時(shi)接通工作，這樣就(jiu)(jiu)可(ke)(ke)以(yi)(yi)確保即(ji)使(shi)在(zai)電(dian)(dian)(dian)(dian)池(chi)沒電(dian)(dian)(dian)(dian)或深度放電(dian)(dian)(dian)(dian)時(shi)，當一插上(shang)電(dian)(dian)(dian)(dian)源，系(xi)統電(dian)(dian)(dian)(dian)源就(jiu)(jiu)能立即(ji)可(ke)(ke)用。外部(bu)檢(jian)測(ce)電(dian)(dian)(dian)(dian)阻器提供輸(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)流和電(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流信(xin)息(xi)，從而使(shi)LTC4000能與(yu)涵蓋mW至kW功(gong)率范(fan)圍(wei)的(de)(de)(de)轉換器一起使(shi)用。

圖4：LTC4000和LTC3789：6V至36V_IN、4節5A鋰離(li)子(zi)電(dian)池(chi)充(chong)電(dian)器

圖5：圖4電路中系統負載為4A時效率隨VIN的變(bian)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(jian)測(ce)功能，從而在大電流應用情況下允許較(jiao)低的檢(jian)測(ce)電壓。

　　結論

　　新式便攜式產品設計(ji)師的(de)(de)工作極富挑戰(zhan)性，尤其(qi)是(shi)(shi)涉及(ji)到電(dian)(dian)(dian)源(yuan)時。客(ke)戶不斷要求(qiu)更多功(gong)能以導致需(xu)要更大(da)(da)的(de)(de)功(gong)率(lv)，結果是(shi)(shi)電(dian)(dian)(dian)池(chi)越來越大(da)(da)。同時，客(ke)戶希望可方便地用幾(ji)乎任(ren)何可用的(de)(de)電(dian)(dian)(dian)源(yuan)給這些電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)。盡管便攜式電(dian)(dian)(dian)源(yuan)領域的(de)(de)這些趨勢造成(cheng)了(le)設計(ji)挑戰(zhan)，但是(shi)(shi)LTC4155和(he)LTC4000讓設計(ji)工作變得簡單多了(le)。在(zai)低(di)壓系統(tong)中，LTC4155高效(xiao)率(lv)地提供高達(da)3.5A的(de)(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流，而(er)且提供很多高性能功(gong)能。LTC4000可構成(cheng)強大(da)(da)的(de)(de)充(chong)電(dian)(dian)(dian)解決方案，而(er)且幾(ji)乎可使用任(ren)何輸入，從(cong)而(er)提供了(le)無與倫比的(de)(de)性能和(he)靈活性。