背景

　　便攜式電(dian)(dian)(dian)(dian)源(yuan)的應用(yong)范圍很廣，也(ye)很多(duo)樣化。產品(pin)包括(kuo)消耗(hao)uW級平均功率的無(wu)線(xian)傳感器節點以及(ji)可(ke)用(yong)小車推著的、電(dian)(dian)(dian)(dian)池組耗(hao)電(dian)(dian)(dian)(dian)數百瓦-時的醫療或數據采(cai)集系統。不(bu)過，盡管應用(yong)種類很多(duo)，仍然出現了幾個趨勢，設計師(shi)日益需要(yao)給產品(pin)提供(gong)更大的功率，以支持不(bu)斷(duan)增多(duo)的功能，同時也(ye)在(zai)考慮怎樣用(yong)任何可(ke)用(yong)電(dian)(dian)(dian)(dian)源(yuan)給電(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)。要(yao)滿(man)足第一(yi)種需求，就要(yao)提高電(dian)(dian)(dian)(dian)池容量(liang)。不(bu)幸(xing)的是，用(yong)戶(hu)大多(duo)比較心(xin)急，容量(liang)提高以后，還必(bi)須在(zai)一(yi)個合理的時間內充滿(man)電(dian)(dian)(dian)(dian)，這就導致要(yao)增大充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流。要(yao)滿(man)足第二種需求，就要(yao)求電(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)解決方案提供(gong)極大的靈活性。本文(wen)將更詳細地討論這些(xie)問題。

　　更大的功率

　　考慮一(yi)下新式(shi)手持式(shi)設(she)備(bei)，面向消費者的(de)(de)(de)(de)(de)(de)設(she)備(bei)和工業設(she)備(bei)都(dou)可(ke)能(neng)包(bao)括(kuo)蜂(feng)窩(wo)電(dian)(dian)(dian)(dian)(dian)話調制解(jie)調器、Wi-Fi模(mo)塊、藍(lan)牙模(mo)塊、大尺寸背光照明(ming)顯(xian)示屏(ping)(ping)…等等。很(hen)(hen)多(duo)(duo)手持式(shi)設(she)備(bei)的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)源(yuan)架構都(dou)與蜂(feng)窩(wo)電(dian)(dian)(dian)(dian)(dian)話的(de)(de)(de)(de)(de)(de)非常相似。一(yi)般情況下，用(yong)一(yi)個3.7V的(de)(de)(de)(de)(de)(de)鋰離子(zi)電(dian)(dian)(dian)(dian)(dian)池作(zuo)為(wei)主電(dian)(dian)(dian)(dian)(dian)源(yuan)，因為(wei)鋰離子(zi)電(dian)(dian)(dian)(dian)(dian)池按重量和按體(ti)積的(de)(de)(de)(de)(de)(de)能(neng)量密度都(dou)很(hen)(hen)高(gao)(單位分別為(wei)Wh/kg和Wh/m3)。過去，很(hen)(hen)多(duo)(duo)大功率(lv)設(she)備(bei)都(dou)采用(yong)7.4V鋰離子(zi)電(dian)(dian)(dian)(dian)(dian)池，以降低(di)電(dian)(dian)(dian)(dian)(dian)流(liu)要求，不過低(di)價(jia)5V電(dian)(dian)(dian)(dian)(dian)源(yuan)管(guan)理IC的(de)(de)(de)(de)(de)(de)上市已經促使越(yue)來越(yue)多(duo)(duo)的(de)(de)(de)(de)(de)(de)手持式(shi)設(she)備(bei)采用(yong)了電(dian)(dian)(dian)(dian)(dian)壓更低(di)的(de)(de)(de)(de)(de)(de)架構。平(ping)板電(dian)(dian)(dian)(dian)(dian)腦很(hen)(hen)好地(di)說明(ming)了這一(yi)點：一(yi)個典型的(de)(de)(de)(de)(de)(de)平(ping)板電(dian)(dian)(dian)(dian)(dian)腦有極多(duo)(duo)的(de)(de)(de)(de)(de)(de)功能(neng)以及非常大的(de)(de)(de)(de)(de)(de)顯(xian)示屏(ping)(ping)(就便攜式(shi)設(she)備(bei)而言(yan))。用(yong)3.7V電(dian)(dian)(dian)(dian)(dian)池供(gong)電(dian)(dian)(dian)(dian)(dian)時(shi)，其容量必須以數千毫安-小時(shi)計(ji)算。為(wei)了在幾個小時(shi)內給這樣一(yi)個電(dian)(dian)(dian)(dian)(dian)池充(chong)滿電(dian)(dian)(dian)(dian)(dian)，需要數千mA的(de)(de)(de)(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)。

　　然而，如果沒有大電流交流適配器，盡管充電電流這么高，也不能防止消費者用USB端口給大功率設備充電的想法。為了滿足這種需求，當交流適配器可用時，電池充電器必須能以大電流(>2A)充電，而在沒有交流適配器可用時，電池充電器必(bi)須(xu)(xu)(xu)仍能高效地利用USB端口提供2.5W至4.5W功(gong)率。此外，器件(jian)必(bi)須(xu)(xu)(xu)保護(hu)敏(min)感的(de)(de)下游低壓(ya)組件(jian)免受可能出(chu)現過壓(ya)情況(kuang)所(suo)導致的(de)(de)損(sun)壞，同時必(bi)須(xu)(xu)(xu)無縫(feng)地將大電(dian)流從USB輸入、交流適配(pei)器或電(dian)池傳送到(dao)負載，并最大限度地降(jiang)低功(gong)耗。另外，該IC還(huan)必(bi)須(xu)(xu)(xu)安全(quan)地管理(li)電(dian)池充電(dian)算法，并監視關(guan)鍵(jian)的(de)(de)系統參數。

　　戰勝單(dan)節電(dian)池供電(dian)的(de)便攜式產(chan)品(pin)在功率(lv)方面的(de)挑戰

　　盡管看似不可能找到能滿足上述要求的單個IC，不過看一下LTC4155，這是一個大功率、I2C控制的高效率電源通路(PowerPath?)管理器、理想二極管控制器和鋰離子電池充電器。該IC用來從各種(zhong)(zhong)5V電(dian)(dian)(dian)源高效(xiao)地(di)傳送高達3A的(de)電(dian)(dian)(dian)流(liu)(liu)，可產生超過3.5A的(de)可用電(dian)(dian)(dian)流(liu)(liu)，以供(gong)電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)和系統(tong)使(shi)用(參見圖1)。LTC4155的(de)效(xiao)率為88%至94%，因此即(ji)使(shi)電(dian)(dian)(dian)流(liu)(liu)值這(zhe)么(me)大，該IC仍(reng)然可以減輕熱量(liang)預算限制(參見圖2)。LTC4155的(de)開關式電(dian)(dian)(dian)源通(tong)路拓撲無縫地(di)管理從兩(liang)種(zhong)(zhong)輸(shu)入電(dian)(dian)(dian)源(例如一個(ge)交(jiao)流(liu)(liu)適配器(qi)和一個(ge)USB端口)到設備中可再充電(dian)(dian)(dian)鋰(li)離子(zi)電(dian)(dian)(dian)池(chi)的(de)配電(dian)(dian)(dian)，同時當輸(shu)入功(gong)率有限時，優先為系統(tong)負載供(gong)電(dian)(dian)(dian)。

　與典型的線性模式充電器相比，LTC4155中開關穩壓器的作用就像一個變壓器，允許VOUT上的負載電流超過輸入電源吸取的電流，并極大地提高電池充電的可用功率。前述例子說明了LTC4155怎樣才能以高達3.5A的電流高效率地充電，以實現更快的充電時間。與普通的開關型電池充電器不同，LTC4155可即(ji)(ji)時接通工作，以確保即(ji)(ji)使(shi)電池(chi)沒電或已深(shen)度放電，當一插上(shang)電源(yuan)插頭，系統(tong)電源(yuan)也立即(ji)(ji)可用。

　　盡管是(shi)以很高的(de)速率(lv)給電(dian)(dian)池(chi)充電(dian)(dian)，監視電(dian)(dian)池(chi)是(shi)否安全也是(shi)很重要(yao)的(de)。當電(dian)(dian)池(chi)溫度降至低(di)于(yu)0°C或升(sheng)至高于(yu)40°C[由一個外部負溫度系數(NTC)熱(re)敏電(dian)(dian)阻測量(liang)]時，LTC4155將自(zi)動停止充電(dian)(dian)。除了這種自(zi)主式(shi)功能，LTC4155還提(ti)供一個7位擴展標(biao)度模數轉換(huan)器(ADC)，以大約1°C的(de)分辨率(lv)監視電(dian)(dian)池(chi)溫度(參見圖(tu)3)。結合4個可用的(de)浮置電(dian)(dian)壓設(she)(she)定值(zhi)和15個電(dian)(dian)池(chi)充電(dian)(dian)電(dian)(dian)流設(she)(she)定值(zhi)，該(gai)ADC可基(ji)于(yu)電(dian)(dian)池(chi)溫度來建(jian)立定制的(de)充電(dian)(dian)算法。

　通過(guo)一個簡單(dan)的(de)(de)(de)兩(liang)線I2C端(duan)口可(ke)獲得NTCADC的(de)(de)(de)結果，從(cong)而能(neng)調(diao)節充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)和(he)電(dian)(dian)(dian)壓的(de)(de)(de)設(she)定值。該(gai)I2C端(duan)口通過(guo)控制16個輸入電(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)設(she)定值(包括USB2.0和(he)3.0兼(jian)容設(she)置)，還可(ke)提(ti)供(gong)USB兼(jian)容性(xing)。該(gai)通信總線允許LTC4155指示額(e)外(wai)的(de)(de)(de)狀態信息，例如(ru)輸入電(dian)(dian)(dian)源狀態、充電(dian)(dian)(dian)器狀態和(he)故障狀態。由于支(zhi)持USBOTG，因(yin)此(ci)無需任何額(e)外(wai)的(de)(de)(de)組(zu)件(jian)，就可(ke)以反過(guo)來向(xiang)USB端(duan)口提(ti)供(gong)5V電(dian)(dian)(dian)源。

　　LTC4155的(de)(de)(de)雙路(lu)輸(shu)入(ru)、優(you)先(xian)(xian)級多路(lu)復用器可(ke)根據用戶(hu)定義的(de)(de)(de)優(you)先(xian)(xian)級(默(mo)認的(de)(de)(de)優(you)先(xian)(xian)級為適(shi)配器輸(shu)入(ru))自主地選擇(ze)最合適(shi)的(de)(de)(de)輸(shu)入(ru)(即墻上適(shi)配器或USB)。過壓保護(OVP)電路(lu)同時保護兩個輸(shu)入(ru)，以免這些(xie)輸(shu)入(ru)因無意間加上的(de)(de)(de)高壓或反(fan)向電壓而(er)損(sun)壞。LTC4155的(de)(de)(de)理想二(er)極管控制器保證即使輸(shu)入(ru)功率(lv)(lv)不(bu)足(zu)或未提(ti)供輸(shu)入(ru)功率(lv)(lv)時，也(ye)始終可(ke)向VOUT提(ti)供足(zu)夠的(de)(de)(de)功率(lv)(lv)。

　　就平板電腦、工業條碼(ma)掃(sao)描器等很(hen)多便(bian)(bian)攜(xie)式應用而言，能(neng)(neng)管(guan)理(li)兩(liang)個(ge)輸入(例(li)如USB和交流(liu)適配器)就足夠了。不過，便(bian)(bian)攜(xie)式設備的設計師(shi)一直在尋求(qiu)用任何可(ke)用電源都能(neng)(neng)給電池充電的方(fang)法

　　多種輸入源

　　用(yong)戶(hu)要(yao)(yao)用(yong)多(duo)種輸(shu)入源(yuan)(yuan)給(gei)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)有幾個原因(yin)。有些(xie)應用(yong)也(ye)許需要(yao)(yao)擺脫(tuo)電(dian)(dian)(dian)(dian)(dian)網的(de)束(shu)縛(fu)，而靠太(tai)陽能電(dian)(dian)(dian)(dian)(dian)池(chi)板(ban)供(gong)電(dian)(dian)(dian)(dian)(dian)。另一(yi)些(xie)應用(yong)則可能要(yao)(yao)求(qiu)(qiu)能方便地(di)用(yong)交流適(shi)配器(qi)(qi)、汽(qi)車(che)電(dian)(dian)(dian)(dian)(dian)池(chi)或高(gao)壓(ya)(ya)(ya)工業及電(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)。無(wu)(wu)論出于(yu)(yu)何種原因(yin)，這要(yao)(yao)求(qiu)(qiu)都給(gei)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)系統增加(jia)了(le)極(ji)大(da)的(de)負擔。大(da)多(duo)數(shu)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)都利用(yong)降壓(ya)(ya)(ya)型(xing)(開關或線性)架(jia)構，用(yong)高(gao)于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)池(chi)最高(gao)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)源(yuan)(yuan)給(gei)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)。以(yi)前(qian)的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)產品輸(shu)入電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)一(yi)般限制(zhi)(zhi)為大(da)約30V。這樣的(de)限制(zhi)(zhi)使(shi)設計師無(wu)(wu)法將電(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)或者具(ju)42V開路(lu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)太(tai)陽能電(dian)(dian)(dian)(dian)(dian)池(chi)板(ban)作為可行的(de)輸(shu)入電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)。在有些(xie)情況下(xia)，希望使(shi)用(yong)的(de)輸(shu)入電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)涵蓋(gai)了(le)高(gao)于(yu)(yu)和低于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)范(fan)圍。設計一(yi)款(kuan)應對此類難題的(de)解決方案通常需要(yao)(yao)混合使(shi)用(yong)高(gao)精(jing)度的(de)電(dian)(dian)(dian)(dian)(dian)流檢(jian)測放大(da)器(qi)(qi)、ADC、一(yi)個用(yong)于(yu)(yu)控制(zhi)(zhi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)的(de)微處理(li)(li)器(qi)(qi)、一(yi)個高(gao)性能DC/DC轉換器(qi)(qi)以(yi)及一(yi)個理(li)(li)想二極(ji)管(guan)或多(duo)路(lu)復用(yong)電(dian)(dian)(dian)(dian)(dian)路(lu)。

　　強大的充電解(jie)決方(fang)案提(ti)供無與倫比的靈活性

　　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(de)典(dian)(dian)型DC/DC轉換器(qi)(qi)拓撲包括但不限于(yu)：降(jiang)壓、升壓、降(jiang)壓-升壓、SEPIC和(he)反激(ji)式(shi)拓撲。該(gai)(gai)器(qi)(qi)件(jian)提供精確的(de)輸(shu)(shu)入(ru)和(he)充電(dian)(dian)電(dian)(dian)流調節，在3V至60V的(de)寬輸(shu)(shu)入(ru)和(he)輸(shu)(shu)出電(dian)(dian)壓范圍內工(gong)作(zuo)，實現了與(yu)各種不同的(de)輸(shu)(shu)入(ru)電(dian)(dian)壓源、以(yi)及不同尺寸(cun)和(he)化學(xue)組成的(de)電(dian)(dian)池組的(de)兼容性(xing)。由于(yu)該(gai)(gai)器(qi)(qi)件(jian)的(de)通用型配置，因此其典(dian)(dian)型應用十分廣(guang)泛(fan)，包括高(gao)功率電(dian)(dian)池充電(dian)(dian)器(qi)(qi)系(xi)統(tong)、高(gao)性(xing)能(neng)便攜式(shi)儀(yi)器(qi)(qi)、電(dian)(dian)池后備系(xi)統(tong)、配有工(gong)業電(dian)(dian)池的(de)設備以(yi)及筆(bi)記(ji)本/小(xiao)型筆(bi)記(ji)本電(dian)(dian)腦。

　　除了(le)可(ke)(ke)以(yi)與很多不同的(de)DC/DC拓撲結合，LTC4000的(de)高(gao)壓能力(li)還(huan)允許該器(qi)件構(gou)成強大和幾乎可(ke)(ke)使(shi)用任何(he)輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(參(can)見(jian)圖4和圖5)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)解決方案。為了(le)確(que)保來自這些輸(shu)(shu)入的(de)功率傳送(song)給合適(shi)的(de)負(fu)載，LTC4000采(cai)用了(le)一種智能電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)通路(lu)拓撲，當(dang)輸(shu)(shu)入功率有限時(shi)，該拓撲可(ke)(ke)優先為系統負(fu)載供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。LTC4000控制外部PFET，以(yi)提供(gong)低損耗反向(xiang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)保護、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)低損耗充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)和放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)以(yi)及(ji)即(ji)時(shi)接通工作，這樣就(jiu)可(ke)(ke)以(yi)確(que)保即(ji)使(shi)在電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)沒電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)或深度放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)，當(dang)一插上電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)，系統電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)就(jiu)能立即(ji)可(ke)(ke)用。外部檢測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻器(qi)提供(gong)輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)信息，從(cong)而(er)使(shi)LTC4000能與涵蓋(gai)mW至kW功率范圍(wei)的(de)轉換器(qi)一起使(shi)用。

　　LTC4000的全功能(neng)電(dian)(dian)池(chi)(chi)充電(dian)(dian)控制器可為各種(zhong)化(hua)(hua)學組成(cheng)的電(dian)(dian)池(chi)(chi)充電(dian)(dian)，包(bao)括(kuo)鋰離子/聚合物(wu)/磷(lin)酸、密封鉛酸(SLA)和鎳(nie)化(hua)(hua)學組成(cheng)。該電(dian)(dian)池(chi)(chi)充電(dian)(dian)器還(huan)提供精確的電(dian)(dian)流檢(jian)測功能(neng)，從而在大電(dian)(dian)流應用情況下允許較低的檢(jian)測電(dian)(dian)壓。

　　結論

　　新式便(bian)攜式產品設(she)計(ji)(ji)師(shi)的(de)(de)工作(zuo)極富挑戰(zhan)性(xing)，尤其是涉及(ji)到電(dian)(dian)(dian)源(yuan)時。客戶不斷要求更多功(gong)能(neng)以導(dao)致需要更大(da)(da)的(de)(de)功(gong)率，結果(guo)是電(dian)(dian)(dian)池越來越大(da)(da)。同(tong)時，客戶希望(wang)可方便(bian)地用幾(ji)乎(hu)任何可用的(de)(de)電(dian)(dian)(dian)源(yuan)給(gei)這(zhe)些(xie)電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)。盡管便(bian)攜式電(dian)(dian)(dian)源(yuan)領域(yu)的(de)(de)這(zhe)些(xie)趨(qu)勢造(zao)成了設(she)計(ji)(ji)挑戰(zhan)，但是LTC4155和LTC4000讓設(she)計(ji)(ji)工作(zuo)變(bian)得(de)簡單多了。在低壓系(xi)統中，LTC4155高(gao)(gao)效率地提供(gong)(gong)高(gao)(gao)達(da)3.5A的(de)(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流，而(er)且提供(gong)(gong)很多高(gao)(gao)性(xing)能(neng)功(gong)能(neng)。LTC4000可構成強大(da)(da)的(de)(de)充(chong)電(dian)(dian)(dian)解(jie)決(jue)方案，而(er)且幾(ji)乎(hu)可使(shi)用任何輸(shu)入，從(cong)而(er)提供(gong)(gong)了無與倫比(bi)的(de)(de)性(xing)能(neng)和靈(ling)活性(xing)。