便攜式電(dian)(dian)(dian)源的(de)(de)應用范圍很廣，也(ye)很多(duo)樣化。產品(pin)包括消耗(hao)uW級平均功率的(de)(de)無線傳感器節(jie)點以及可(ke)用小車推著的(de)(de)、電(dian)(dian)(dian)池組耗(hao)電(dian)(dian)(dian)數(shu)百瓦(wa)-時的(de)(de)醫療(liao)或(huo)數(shu)據采集系(xi)統。不(bu)過，盡(jin)管(guan)應用種類很多(duo)，仍然出現了幾(ji)個趨勢，設計師日益(yi)需(xu)(xu)要(yao)給(gei)產品(pin)提(ti)供更大(da)(da)的(de)(de)功率，以支持不(bu)斷增多(duo)的(de)(de)功能，同(tong)時也(ye)在(zai)考慮怎(zen)樣用任何可(ke)用電(dian)(dian)(dian)源給(gei)電(dian)(dian)(dian)池充電(dian)(dian)(dian)。要(yao)滿(man)足(zu)(zu)第(di)一(yi)種需(xu)(xu)求(qiu)(qiu)(qiu)，就要(yao)提(ti)高(gao)(gao)電(dian)(dian)(dian)池容量。不(bu)幸(xing)的(de)(de)是，用戶大(da)(da)多(duo)比較心急，容量提(ti)高(gao)(gao)以后(hou)，還必須在(zai)一(yi)個合理的(de)(de)時間內充滿(man)電(dian)(dian)(dian)，這就導致要(yao)增大(da)(da)充電(dian)(dian)(dian)電(dian)(dian)(dian)流。要(yao)滿(man)足(zu)(zu)第(di)二種需(xu)(xu)求(qiu)(qiu)(qiu)，就要(yao)求(qiu)(qiu)(qiu)電(dian)(dian)(dian)池充電(dian)(dian)(dian)解決方案(an)提(ti)供極大(da)(da)的(de)(de)靈(ling)活性。本文將更詳細地討論這些(xie)問題。

　　更大的功率

　　考慮一(yi)(yi)(yi)下新式(shi)(shi)手(shou)(shou)(shou)持(chi)(chi)式(shi)(shi)設備(bei)(bei)，面向消(xiao)費者的(de)設備(bei)(bei)和(he)工業設備(bei)(bei)都(dou)(dou)可(ke)能(neng)包(bao)括(kuo)蜂(feng)窩電(dian)(dian)(dian)(dian)(dian)話調制解(jie)調器、Wi-Fi模塊、藍牙模塊、大(da)(da)尺(chi)寸背光照(zhao)明(ming)顯示(shi)屏…等(deng)等(deng)。很(hen)多(duo)手(shou)(shou)(shou)持(chi)(chi)式(shi)(shi)設備(bei)(bei)的(de)電(dian)(dian)(dian)(dian)(dian)源架構(gou)都(dou)(dou)與蜂(feng)窩電(dian)(dian)(dian)(dian)(dian)話的(de)非常(chang)相(xiang)似。一(yi)(yi)(yi)般情況下，用(yong)一(yi)(yi)(yi)個3.7V的(de)鋰離子電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)作為(wei)主電(dian)(dian)(dian)(dian)(dian)源，因為(wei)鋰離子電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)按重量和(he)按體(ti)積的(de)能(neng)量密度(du)都(dou)(dou)很(hen)高(單位分別為(wei)Wh/kg和(he)Wh/m3)。過去，很(hen)多(duo)大(da)(da)功率設備(bei)(bei)都(dou)(dou)采用(yong)7.4V鋰離子電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)，以降低(di)電(dian)(dian)(dian)(dian)(dian)流(liu)要求，不過低(di)價5V電(dian)(dian)(dian)(dian)(dian)源管理(li)IC的(de)上市已經促使越來越多(duo)的(de)手(shou)(shou)(shou)持(chi)(chi)式(shi)(shi)設備(bei)(bei)采用(yong)了(le)(le)(le)電(dian)(dian)(dian)(dian)(dian)壓(ya)更低(di)的(de)架構(gou)。平(ping)板電(dian)(dian)(dian)(dian)(dian)腦(nao)很(hen)好地說(shuo)明(ming)了(le)(le)(le)這一(yi)(yi)(yi)點：一(yi)(yi)(yi)個典型的(de)平(ping)板電(dian)(dian)(dian)(dian)(dian)腦(nao)有極(ji)多(duo)的(de)功能(neng)以及(ji)非常(chang)大(da)(da)的(de)顯示(shi)屏(就便攜(xie)式(shi)(shi)設備(bei)(bei)而言)。用(yong)3.7V電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)供電(dian)(dian)(dian)(dian)(dian)時，其(qi)容量必須以數(shu)千(qian)毫安-小時計算。為(wei)了(le)(le)(le)在幾個小時內給(gei)這樣一(yi)(yi)(yi)個電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充滿電(dian)(dian)(dian)(dian)(dian)，需要數(shu)千(qian)mA的(de)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)。

　　然而(er)，如果沒有大電(dian)(dian)流(liu)(liu)交(jiao)流(liu)(liu)適配(pei)器，盡管(guan)充電(dian)(dian)電(dian)(dian)流(liu)(liu)這(zhe)么高，也不能(neng)(neng)防(fang)止消(xiao)費者用(yong)USB端口給大功(gong)率(lv)(lv)設備充電(dian)(dian)的(de)想法。為(wei)了滿(man)足(zu)這(zhe)種需求，當交(jiao)流(liu)(liu)適配(pei)器可用(yong)時，電(dian)(dian)池(chi)充電(dian)(dian)器必(bi)(bi)須(xu)能(neng)(neng)以(yi)大電(dian)(dian)流(liu)(liu)(>2A)充電(dian)(dian)，而(er)在(zai)沒有交(jiao)流(liu)(liu)適配(pei)器可用(yong)時，電(dian)(dian)池(chi)充電(dian)(dian)器必(bi)(bi)須(xu)仍(reng)能(neng)(neng)高效(xiao)地(di)(di)利用(yong)USB端口提供2.5W至4.5W功(gong)率(lv)(lv)。此外，器件必(bi)(bi)須(xu)保護敏感的(de)下游低壓組件免受可能(neng)(neng)出現過壓情況所導(dao)致的(de)損壞，同(tong)時必(bi)(bi)須(xu)無縫地(di)(di)將大電(dian)(dian)流(liu)(liu)從USB輸入、交(jiao)流(liu)(liu)適配(pei)器或電(dian)(dian)池(chi)傳送到負載，并最大限(xian)度(du)地(di)(di)降(jiang)低功(gong)耗。另外，該IC還必(bi)(bi)須(xu)安全地(di)(di)管(guan)理電(dian)(dian)池(chi)充電(dian)(dian)算法，并監(jian)視關鍵的(de)系統參數。

　　戰勝單節電(dian)池供電(dian)的(de)便攜式產(chan)品在功率方面的(de)挑戰

　　盡管(guan)(guan)(guan)看(kan)似不可(ke)能(neng)找到(dao)能(neng)滿足上述(shu)要求的(de)(de)(de)單(dan)個(ge)(ge)IC，不過看(kan)一(yi)下(xia)LTC4155，這是一(yi)個(ge)(ge)大(da)(da)功率(lv)(lv)(lv)(lv)、I2C控制(zhi)(zhi)的(de)(de)(de)高(gao)效率(lv)(lv)(lv)(lv)電(dian)(dian)(dian)(dian)源(yuan)通路(lu)(PowerPath?)管(guan)(guan)(guan)理器、理想二極管(guan)(guan)(guan)控制(zhi)(zhi)器和(he)鋰(li)離(li)子(zi)電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)器。該(gai)(gai)IC用來從各種5V電(dian)(dian)(dian)(dian)源(yuan)高(gao)效地(di)傳(chuan)送高(gao)達3A的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)，可(ke)產(chan)生(sheng)超過3.5A的(de)(de)(de)可(ke)用電(dian)(dian)(dian)(dian)流(liu)，以供電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)和(he)系統使(shi)用(參見圖(tu)1)。LTC4155的(de)(de)(de)效率(lv)(lv)(lv)(lv)為88%至94%，因此即使(shi)電(dian)(dian)(dian)(dian)流(liu)值這么(me)大(da)(da)，該(gai)(gai)IC仍然可(ke)以減輕熱量預(yu)算限(xian)制(zhi)(zhi)(參見圖(tu)2)。LTC4155的(de)(de)(de)開關式電(dian)(dian)(dian)(dian)源(yuan)通路(lu)拓撲無縫地(di)管(guan)(guan)(guan)理從兩種輸入(ru)(ru)電(dian)(dian)(dian)(dian)源(yuan)(例如(ru)一(yi)個(ge)(ge)交流(liu)適配(pei)器和(he)一(yi)個(ge)(ge)USB端口(kou))到(dao)設備(bei)中(zhong)可(ke)再充(chong)電(dian)(dian)(dian)(dian)鋰(li)離(li)子(zi)電(dian)(dian)(dian)(dian)池的(de)(de)(de)配(pei)電(dian)(dian)(dian)(dian)，同(tong)時(shi)當輸入(ru)(ru)功率(lv)(lv)(lv)(lv)有限(xian)時(shi)，優先為系統負載供電(dian)(dian)(dian)(dian)。

圖1：LTC4155的(de)典型應用(yong)電(dian)路(lu)

圖2：LTC4155的(de)典型效率

　　與典型的(de)(de)(de)線性模式充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)相(xiang)比，LTC4155中開關穩壓器(qi)的(de)(de)(de)作用就像一個變(bian)壓器(qi)，允許VOUT上的(de)(de)(de)負載電(dian)(dian)(dian)(dian)流(liu)(liu)超過輸入(ru)電(dian)(dian)(dian)(dian)源(yuan)吸取的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)，并極大地提高電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)(de)(de)可(ke)用功率。前述例子說明了(le)LTC4155怎樣(yang)才能以(yi)高達3.5A的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)高效率地充(chong)(chong)電(dian)(dian)(dian)(dian)，以(yi)實現更快的(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)間。與普通(tong)的(de)(de)(de)開關型電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)不(bu)同，LTC4155可(ke)即(ji)時(shi)接通(tong)工作，以(yi)確(que)保即(ji)使電(dian)(dian)(dian)(dian)池(chi)沒電(dian)(dian)(dian)(dian)或已深(shen)度放(fang)電(dian)(dian)(dian)(dian)，當(dang)一插上電(dian)(dian)(dian)(dian)源(yuan)插頭(tou)，系統電(dian)(dian)(dian)(dian)源(yuan)也立即(ji)可(ke)用。

　　盡(jin)管是(shi)以很高(gao)的(de)(de)速率給電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)，監視(shi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)是(shi)否安(an)全也是(shi)很重要的(de)(de)。當電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)溫(wen)度(du)降至低于0°C或(huo)升至高(gao)于40°C[由一(yi)個外部負溫(wen)度(du)系數(NTC)熱敏電(dian)(dian)(dian)(dian)(dian)阻測(ce)量]時，LTC4155將自動停止充(chong)電(dian)(dian)(dian)(dian)(dian)。除了這種自主式功(gong)能(neng)，LTC4155還提(ti)供一(yi)個7位擴展標度(du)模數轉換器(ADC)，以大(da)約1°C的(de)(de)分(fen)辨率監視(shi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)溫(wen)度(du)(參見圖3)。結(jie)合4個可用的(de)(de)浮置電(dian)(dian)(dian)(dian)(dian)壓設(she)定(ding)值和15個電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流設(she)定(ding)值，該ADC可基于電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)溫(wen)度(du)來建立定(ding)制的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)算法。

圖3：7位熱敏電阻器ADC顯示LTC4155的預置溫度跳變點

　　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(zhang)狀(zhuang)態。由于支持USBOTG，因此無需任何額外的組件，就可以反過來向USB端(duan)口提供(gong)5V電(dian)源。

　　LTC4155的(de)(de)(de)(de)雙路輸(shu)入(ru)、優(you)先(xian)級(ji)(ji)多路復用器(qi)可(ke)根據用戶定義的(de)(de)(de)(de)優(you)先(xian)級(ji)(ji)(默(mo)認的(de)(de)(de)(de)優(you)先(xian)級(ji)(ji)為(wei)適(shi)配器(qi)輸(shu)入(ru))自主(zhu)地選擇最合(he)適(shi)的(de)(de)(de)(de)輸(shu)入(ru)(即墻(qiang)上(shang)適(shi)配器(qi)或USB)。過壓保護(OVP)電路同時保護兩個(ge)輸(shu)入(ru)，以(yi)免(mian)這些輸(shu)入(ru)因(yin)無意(yi)間加上(shang)的(de)(de)(de)(de)高(gao)壓或反向電壓而(er)損(sun)壞。LTC4155的(de)(de)(de)(de)理想二極(ji)管(guan)控制(zhi)器(qi)保證即使輸(shu)入(ru)功率不足或未提供輸(shu)入(ru)功率時，也(ye)始終可(ke)向VOUT提供足夠(gou)的(de)(de)(de)(de)功率。

　　就平板(ban)電(dian)腦、工業條(tiao)碼掃(sao)描器等很多(duo)便(bian)(bian)攜式應(ying)用(yong)而言，能管理兩個輸入(例如USB和交流適配器)就足夠了。不(bu)過(guo)，便(bian)(bian)攜式設備的設計師(shi)一直在尋(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)戶要(yao)用(yong)多種輸(shu)(shu)入(ru)源給電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)有幾個(ge)原因。有些(xie)(xie)應用(yong)也許(xu)需(xu)要(yao)擺脫(tuo)電(dian)(dian)(dian)(dian)網(wang)的(de)(de)(de)束縛，而(er)靠(kao)太陽能(neng)(neng)電(dian)(dian)(dian)(dian)池(chi)(chi)板(ban)供電(dian)(dian)(dian)(dian)。另一(yi)(yi)些(xie)(xie)應用(yong)則可能(neng)(neng)要(yao)求(qiu)能(neng)(neng)方便地用(yong)交流適配(pei)器、汽車(che)電(dian)(dian)(dian)(dian)池(chi)(chi)或高壓(ya)(ya)工業(ye)及電(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)源充(chong)電(dian)(dian)(dian)(dian)。無(wu)論出于(yu)何種原因，這要(yao)求(qiu)都給電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)系(xi)統增加了極大的(de)(de)(de)負擔。大多數電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)器都利用(yong)降壓(ya)(ya)型(開(kai)(kai)關或線(xian)性)架(jia)構，用(yong)高于(yu)電(dian)(dian)(dian)(dian)池(chi)(chi)最高電(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya)(ya)源給電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)。以(yi)前的(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)器產品(pin)輸(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)壓(ya)(ya)一(yi)(yi)般限制(zhi)(zhi)為大約30V。這樣的(de)(de)(de)限制(zhi)(zhi)使(shi)設(she)(she)計(ji)師無(wu)法(fa)將電(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)源或者具42V開(kai)(kai)路(lu)電(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)太陽能(neng)(neng)電(dian)(dian)(dian)(dian)池(chi)(chi)板(ban)作為可行(xing)的(de)(de)(de)輸(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)源。在(zai)有些(xie)(xie)情況下，希望使(shi)用(yong)的(de)(de)(de)輸(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓(ya)(ya)涵蓋了高于(yu)和低于(yu)電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)范圍。設(she)(she)計(ji)一(yi)(yi)款應對此類難題(ti)的(de)(de)(de)解(jie)決方案(an)通(tong)常(chang)需(xu)要(yao)混合使(shi)用(yong)高精度的(de)(de)(de)電(dian)(dian)(dian)(dian)流檢測(ce)放(fang)大器、ADC、一(yi)(yi)個(ge)用(yong)于(yu)控(kong)制(zhi)(zhi)充(chong)電(dian)(dian)(dian)(dian)的(de)(de)(de)微處理器、一(yi)(yi)個(ge)高性能(neng)(neng)DC/DC轉換器以(yi)及一(yi)(yi)個(ge)理想二(er)極管或多路(lu)復用(yong)電(dian)(dian)(dian)(dian)路(lu)。

　　強大的充電解決(jue)方案提供(gong)無與倫比(bi)的靈活性(xing)

　　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)性能便攜(xie)式(shi)儀器、電(dian)池后備系統、配有工業電(dian)池的設備以及(ji)筆(bi)記本/小型筆(bi)記本電(dian)腦(nao)。

　　除了可以(yi)與(yu)很(hen)多不同的(de)DC/DC拓撲(pu)結合，LTC4000的(de)高壓(ya)能(neng)(neng)力還允許(xu)該器(qi)件構成(cheng)強大(da)和幾(ji)乎可使用任(ren)何輸(shu)(shu)入電(dian)(dian)(dian)(dian)源(yuan)(參見(jian)圖4和圖5)的(de)電(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)解決方案。為了確保來自(zi)這(zhe)些輸(shu)(shu)入的(de)功率(lv)(lv)(lv)傳送(song)給合適的(de)負(fu)載(zai)，LTC4000采(cai)用了一(yi)種智能(neng)(neng)電(dian)(dian)(dian)(dian)源(yuan)通路拓撲(pu)，當(dang)(dang)輸(shu)(shu)入功率(lv)(lv)(lv)有限時(shi)，該拓撲(pu)可優先為系統(tong)負(fu)載(zai)供電(dian)(dian)(dian)(dian)。LTC4000控(kong)制外部PFET，以(yi)提(ti)供低損耗(hao)反向電(dian)(dian)(dian)(dian)流保護(hu)、電(dian)(dian)(dian)(dian)池(chi)的(de)低損耗(hao)充電(dian)(dian)(dian)(dian)和放電(dian)(dian)(dian)(dian)以(yi)及即(ji)時(shi)接(jie)通工(gong)作，這(zhe)樣就可以(yi)確保即(ji)使在電(dian)(dian)(dian)(dian)池(chi)沒電(dian)(dian)(dian)(dian)或深度放電(dian)(dian)(dian)(dian)時(shi)，當(dang)(dang)一(yi)插上電(dian)(dian)(dian)(dian)源(yuan)，系統(tong)電(dian)(dian)(dian)(dian)源(yuan)就能(neng)(neng)立即(ji)可用。外部檢測(ce)電(dian)(dian)(dian)(dian)阻器(qi)提(ti)供輸(shu)(shu)入電(dian)(dian)(dian)(dian)流和電(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流信息，從而使LTC4000能(neng)(neng)與(yu)涵蓋mW至kW功率(lv)(lv)(lv)范(fan)圍(wei)的(de)轉換器(qi)一(yi)起使用。

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

圖(tu)5：圖(tu)4電路(lu)中系(xi)統(tong)負載為(wei)4A時效(xiao)率隨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(huan)提供精確的電(dian)流檢測功能，從而在(zai)大(da)電(dian)流應用(yong)情況下允許較低的檢測電(dian)壓。

　　結論

　　新式(shi)便攜式(shi)產品設計師的(de)工作極富挑(tiao)戰(zhan)性(xing)，尤其是(shi)涉及到電(dian)(dian)源時。客戶不斷(duan)要求更多功能以導(dao)致(zhi)需要更大的(de)功率(lv)，結果是(shi)電(dian)(dian)池(chi)越來越大。同時，客戶希望可方便地用幾乎(hu)任何(he)可用的(de)電(dian)(dian)源給(gei)這些(xie)電(dian)(dian)池(chi)充電(dian)(dian)。盡(jin)管便攜式(shi)電(dian)(dian)源領域的(de)這些(xie)趨勢造成(cheng)了設計挑(tiao)戰(zhan)，但是(shi)LTC4155和LTC4000讓(rang)設計工作變得簡單多了。在低壓系統中，LTC4155高效率(lv)地提供高達3.5A的(de)充電(dian)(dian)電(dian)(dian)流，而(er)且(qie)提供很多高性(xing)能功能。LTC4000可構(gou)成(cheng)強大的(de)充電(dian)(dian)解決方案，而(er)且(qie)幾乎(hu)可使用任何(he)輸入，從而(er)提供了無與倫(lun)比的(de)性(xing)能和靈活性(xing)。