背景

　　便(bian)攜式電(dian)(dian)源(yuan)的(de)(de)(de)(de)應(ying)用(yong)(yong)范圍很(hen)廣，也(ye)很(hen)多(duo)樣(yang)化。產品包括消(xiao)耗uW級平均(jun)功率的(de)(de)(de)(de)無線傳(chuan)感器節點以及可(ke)用(yong)(yong)小車推著(zhu)的(de)(de)(de)(de)、電(dian)(dian)池組耗電(dian)(dian)數百瓦-時的(de)(de)(de)(de)醫(yi)療(liao)或數據(ju)采集系統。不過，盡管應(ying)用(yong)(yong)種類很(hen)多(duo)，仍然出現了幾個趨勢，設計師日益需(xu)要(yao)(yao)給(gei)產品提供更(geng)大的(de)(de)(de)(de)功率，以支持不斷(duan)增多(duo)的(de)(de)(de)(de)功能，同時也(ye)在考慮怎(zen)樣(yang)用(yong)(yong)任(ren)何可(ke)用(yong)(yong)電(dian)(dian)源(yuan)給(gei)電(dian)(dian)池充電(dian)(dian)。要(yao)(yao)滿(man)足(zu)第一(yi)種需(xu)求(qiu)，就要(yao)(yao)提高電(dian)(dian)池容量。不幸的(de)(de)(de)(de)是，用(yong)(yong)戶大多(duo)比(bi)較心急，容量提高以后，還必須在一(yi)個合理(li)的(de)(de)(de)(de)時間內充滿(man)電(dian)(dian)，這就導致要(yao)(yao)增大充電(dian)(dian)電(dian)(dian)流。要(yao)(yao)滿(man)足(zu)第二種需(xu)求(qiu)，就要(yao)(yao)求(qiu)電(dian)(dian)池充電(dian)(dian)解決方案提供極大的(de)(de)(de)(de)靈活性(xing)。本文(wen)將更(geng)詳細地討論(lun)這些問題。

　　更大的功率

　　考(kao)慮一下新式(shi)手(shou)持(chi)式(shi)設(she)備(bei)，面向(xiang)消費(fei)者的(de)設(she)備(bei)和(he)(he)(he)工業設(she)備(bei)都可能(neng)包括蜂窩電(dian)(dian)話(hua)調制解調器、Wi-Fi模塊、藍牙模塊、大尺寸背光照明(ming)顯示(shi)屏(ping)…等等。很(hen)多(duo)手(shou)持(chi)式(shi)設(she)備(bei)的(de)電(dian)(dian)源架構(gou)都與(yu)蜂窩電(dian)(dian)話(hua)的(de)非常相似(si)。一般情況(kuang)下，用(yong)一個(ge)3.7V的(de)鋰(li)離(li)子電(dian)(dian)池(chi)作為(wei)主電(dian)(dian)源，因為(wei)鋰(li)離(li)子電(dian)(dian)池(chi)按(an)重量和(he)(he)(he)按(an)體積的(de)能(neng)量密度(du)都很(hen)高(單位分別(bie)為(wei)Wh/kg和(he)(he)(he)Wh/m3)。過去，很(hen)多(duo)大功率設(she)備(bei)都采用(yong)7.4V鋰(li)離(li)子電(dian)(dian)池(chi)，以(yi)降低電(dian)(dian)流(liu)(liu)要求，不過低價5V電(dian)(dian)源管(guan)理IC的(de)上市已經(jing)促使越(yue)來越(yue)多(duo)的(de)手(shou)持(chi)式(shi)設(she)備(bei)采用(yong)了電(dian)(dian)壓更低的(de)架構(gou)。平(ping)板(ban)電(dian)(dian)腦很(hen)好地說明(ming)了這一點(dian)：一個(ge)典型的(de)平(ping)板(ban)電(dian)(dian)腦有極多(duo)的(de)功能(neng)以(yi)及非常大的(de)顯示(shi)屏(ping)(就便攜式(shi)設(she)備(bei)而(er)言(yan))。用(yong)3.7V電(dian)(dian)池(chi)供電(dian)(dian)時(shi)，其容(rong)量必須以(yi)數(shu)千毫安-小時(shi)計算。為(wei)了在幾(ji)個(ge)小時(shi)內給(gei)這樣(yang)一個(ge)電(dian)(dian)池(chi)充滿(man)電(dian)(dian)，需要數(shu)千mA的(de)充電(dian)(dian)電(dian)(dian)流(liu)(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)仍能高效地利(li)用USB端口提供(gong)2.5W至4.5W功(gong)率。此(ci)外(wai)(wai)，器(qi)件(jian)(jian)必(bi)須(xu)保(bao)護敏感的(de)下游低(di)壓組(zu)件(jian)(jian)免(mian)受(shou)可能出現過(guo)壓情況所導致的(de)損(sun)壞，同時必(bi)須(xu)無縫地將(jiang)大電(dian)流從USB輸(shu)入、交流適(shi)配器(qi)或電(dian)池(chi)傳(chuan)送到負載，并(bing)最(zui)大限(xian)度地降(jiang)低(di)功(gong)耗。另(ling)外(wai)(wai)，該IC還必(bi)須(xu)安(an)全地管理電(dian)池(chi)充電(dian)算法，并(bing)監視關鍵的(de)系統參數。

　　戰勝單節(jie)電(dian)池供電(dian)的(de)(de)便攜式產(chan)品(pin)在(zai)功率方面的(de)(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5V電(dian)源(yuan)高(gao)效地(di)傳送(song)高(gao)達3A的(de)電(dian)流，可產生超過(guo)3.5A的(de)可用電(dian)流，以(yi)供(gong)電(dian)池充(chong)電(dian)和(he)系(xi)統使用(參見(jian)(jian)圖(tu)1)。LTC4155的(de)效率為88%至94%，因此即使電(dian)流值這(zhe)么大(da)，該IC仍然可以(yi)減輕熱(re)量預(yu)算限(xian)制(參見(jian)(jian)圖(tu)2)。LTC4155的(de)開關式(shi)電(dian)源(yuan)通路拓撲無縫地(di)管理(li)從兩種輸入電(dian)源(yuan)(例(li)如一個交流適(shi)配器和(he)一個USB端口)到設備中可再充(chong)電(dian)鋰(li)離子(zi)電(dian)池的(de)配電(dian)，同時當輸入功率有限(xian)時，優先為系(xi)統負載供(gong)電(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(tong)，LTC4155可即(ji)(ji)時接通工作，以確保即(ji)(ji)使(shi)電(dian)池沒電(dian)或已深度放電(dian)，當一插上電(dian)源插頭，系統電(dian)源也立即(ji)(ji)可用。

　　盡管(guan)是(shi)以很(hen)(hen)高(gao)的(de)(de)速(su)率給(gei)電(dian)池(chi)充電(dian)，監視(shi)電(dian)池(chi)是(shi)否(fou)安全也是(shi)很(hen)(hen)重要的(de)(de)。當電(dian)池(chi)溫(wen)度(du)降至低于0°C或升至高(gao)于40°C[由一個外部(bu)負溫(wen)度(du)系數(NTC)熱敏電(dian)阻測量]時(shi)，LTC4155將自動停(ting)止充電(dian)。除了這(zhe)種自主式功能，LTC4155還提供一個7位擴展標度(du)模數轉換器(ADC)，以大約1°C的(de)(de)分辨率監視(shi)電(dian)池(chi)溫(wen)度(du)(參(can)見(jian)圖3)。結合4個可用的(de)(de)浮置電(dian)壓設定值(zhi)和(he)15個電(dian)池(chi)充電(dian)電(dian)流設定值(zhi)，該ADC可基于電(dian)池(chi)溫(wen)度(du)來建立(li)定制的(de)(de)充電(dian)算法。

　通(tong)過一個簡單的(de)(de)兩線I2C端口可(ke)(ke)獲得NTCADC的(de)(de)結果，從而(er)能調節充(chong)電(dian)(dian)電(dian)(dian)流和電(dian)(dian)壓的(de)(de)設(she)定(ding)值(zhi)。該(gai)I2C端口通(tong)過控制16個輸入電(dian)(dian)流的(de)(de)設(she)定(ding)值(zhi)(包(bao)括USB2.0和3.0兼容(rong)設(she)置)，還可(ke)(ke)提供USB兼容(rong)性。該(gai)通(tong)信總線允許(xu)LTC4155指示(shi)額外(wai)的(de)(de)狀態信息，例如輸入電(dian)(dian)源狀態、充(chong)電(dian)(dian)器狀態和故障狀態。由于支持USBOTG，因此無(wu)需(xu)任何額外(wai)的(de)(de)組件(jian)，就可(ke)(ke)以反過來向USB端口提供5V電(dian)(dian)源。

　　LTC4155的(de)雙路輸入、優先級(ji)多路復用器可根(gen)據用戶定義的(de)優先級(ji)(默(mo)認的(de)優先級(ji)為(wei)適配(pei)器輸入)自主(zhu)地選擇最合適的(de)輸入(即墻上(shang)適配(pei)器或USB)。過壓(ya)保(bao)護(OVP)電(dian)路同時保(bao)護兩個輸入，以免這些輸入因無(wu)意間加上(shang)的(de)高壓(ya)或反向(xiang)電(dian)壓(ya)而損壞。LTC4155的(de)理想二極管控(kong)制(zhi)器保(bao)證即使輸入功(gong)率(lv)(lv)不足或未提供輸入功(gong)率(lv)(lv)時，也始終可向(xiang)VOUT提供足夠的(de)功(gong)率(lv)(lv)。

　　就平板電(dian)腦(nao)、工業條碼掃描器等很(hen)多便攜式應用(yong)而言，能(neng)管理兩個(ge)輸(shu)入(例如USB和交流適配器)就足夠了。不(bu)過，便攜式設備的(de)設計師一直在尋(xun)求用(yong)任何可用(yong)電(dian)源都能(neng)給電(dian)池充電(dian)的(de)方法(fa)

　　多種輸入源

　　用(yong)(yong)戶要(yao)用(yong)(yong)多種輸(shu)入(ru)源給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)有幾個(ge)(ge)原因。有些應(ying)用(yong)(yong)也許需要(yao)擺脫(tuo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)網的(de)(de)束縛，而靠太(tai)陽能(neng)(neng)(neng)(neng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)板供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。另一(yi)(yi)些應(ying)用(yong)(yong)則可能(neng)(neng)(neng)(neng)要(yao)求能(neng)(neng)(neng)(neng)方便地(di)用(yong)(yong)交流適(shi)配器(qi)、汽(qi)車電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)或高(gao)(gao)壓(ya)(ya)(ya)(ya)工業及電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。無論出于(yu)(yu)(yu)何種原因，這要(yao)求都給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)系統增(zeng)加了(le)極大的(de)(de)負擔。大多數(shu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)都利用(yong)(yong)降壓(ya)(ya)(ya)(ya)型(開關(guan)或線性(xing))架構，用(yong)(yong)高(gao)(gao)于(yu)(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)最高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)源給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。以(yi)前(qian)的(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)產品輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)一(yi)(yi)般限(xian)制(zhi)為大約30V。這樣(yang)的(de)(de)限(xian)制(zhi)使(shi)設(she)計師無法將電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源或者(zhe)具42V開路(lu)(lu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)的(de)(de)太(tai)陽能(neng)(neng)(neng)(neng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)板作為可行的(de)(de)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源。在有些情況下，希望使(shi)用(yong)(yong)的(de)(de)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)涵蓋(gai)了(le)高(gao)(gao)于(yu)(yu)(yu)和低于(yu)(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)的(de)(de)范圍(wei)。設(she)計一(yi)(yi)款應(ying)對此類難題的(de)(de)解決方案通常需要(yao)混合使(shi)用(yong)(yong)高(gao)(gao)精度(du)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流檢測放大器(qi)、ADC、一(yi)(yi)個(ge)(ge)用(yong)(yong)于(yu)(yu)(yu)控制(zhi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)微處理器(qi)、一(yi)(yi)個(ge)(ge)高(gao)(gao)性(xing)能(neng)(neng)(neng)(neng)DC/DC轉換(huan)器(qi)以(yi)及一(yi)(yi)個(ge)(ge)理想二極管或多路(lu)(lu)復用(yong)(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。

　　強大的充電解決方案(an)提(ti)供無(wu)與倫比(bi)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)(de)(de)典型(xing)DC/DC轉換(huan)器拓撲(pu)包括但不限于：降壓、升(sheng)壓、降壓-升(sheng)壓、SEPIC和(he)反激式拓撲(pu)。該器件(jian)提供精確的(de)(de)(de)輸(shu)入(ru)和(he)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流調(diao)節，在3V至60V的(de)(de)(de)寬輸(shu)入(ru)和(he)輸(shu)出(chu)電(dian)(dian)(dian)壓范(fan)圍(wei)內工(gong)作，實現了與(yu)各種不同(tong)的(de)(de)(de)輸(shu)入(ru)電(dian)(dian)(dian)壓源、以及不同(tong)尺(chi)寸(cun)和(he)化學組(zu)成的(de)(de)(de)電(dian)(dian)(dian)池(chi)(chi)組(zu)的(de)(de)(de)兼容性。由于該器件(jian)的(de)(de)(de)通用型(xing)配置(zhi)，因此(ci)其典型(xing)應(ying)用十分廣泛，包括高功(gong)率電(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)器系統、高性能便攜式儀器、電(dian)(dian)(dian)池(chi)(chi)后備系統、配有工(gong)業電(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)設備以及筆(bi)記本/小(xiao)型(xing)筆(bi)記本電(dian)(dian)(dian)腦。

　　除(chu)了(le)可(ke)以與很多不同的(de)(de)DC/DC拓撲(pu)結(jie)合(he)，LTC4000的(de)(de)高壓能力(li)還允(yun)許(xu)該(gai)器件構(gou)成強大和幾乎可(ke)使用(yong)任何輸(shu)入(ru)電(dian)(dian)(dian)源(yuan)(yuan)(參見圖4和圖5)的(de)(de)電(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)解決方案。為(wei)了(le)確保(bao)來自這些輸(shu)入(ru)的(de)(de)功率(lv)(lv)傳送給合(he)適的(de)(de)負(fu)載，LTC4000采用(yong)了(le)一(yi)種智(zhi)能電(dian)(dian)(dian)源(yuan)(yuan)通路(lu)拓撲(pu)，當輸(shu)入(ru)功率(lv)(lv)有限(xian)時(shi)，該(gai)拓撲(pu)可(ke)優先為(wei)系統負(fu)載供電(dian)(dian)(dian)。LTC4000控制外(wai)部PFET，以提供低損耗(hao)反向電(dian)(dian)(dian)流保(bao)護、電(dian)(dian)(dian)池(chi)(chi)的(de)(de)低損耗(hao)充(chong)電(dian)(dian)(dian)和放電(dian)(dian)(dian)以及(ji)即時(shi)接通工作(zuo)，這樣(yang)就(jiu)可(ke)以確保(bao)即使在電(dian)(dian)(dian)池(chi)(chi)沒(mei)電(dian)(dian)(dian)或深(shen)度放電(dian)(dian)(dian)時(shi)，當一(yi)插上電(dian)(dian)(dian)源(yuan)(yuan)，系統電(dian)(dian)(dian)源(yuan)(yuan)就(jiu)能立即可(ke)用(yong)。外(wai)部檢測電(dian)(dian)(dian)阻(zu)器提供輸(shu)入(ru)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(cong)而使LTC4000能與涵蓋mW至kW功率(lv)(lv)范圍的(de)(de)轉換器一(yi)起使用(yong)。

　　LTC4000的(de)全功能電(dian)(dian)池(chi)充電(dian)(dian)控(kong)制器可(ke)為(wei)各種化學組(zu)成的(de)電(dian)(dian)池(chi)充電(dian)(dian)，包括鋰離子/聚合物/磷酸、密封鉛(qian)酸(SLA)和鎳化學組(zu)成。該(gai)電(dian)(dian)池(chi)充電(dian)(dian)器還提(ti)供(gong)精確的(de)電(dian)(dian)流檢測(ce)功能，從而在(zai)大電(dian)(dian)流應用情況下允許較低的(de)檢測(ce)電(dian)(dian)壓。

　　結論

　　新式便(bian)攜式產品設計(ji)(ji)師的(de)(de)(de)工作極富挑戰性(xing)，尤其(qi)是(shi)涉(she)及到電(dian)(dian)源時(shi)。客戶不斷要求更多(duo)(duo)功能(neng)以導(dao)致需(xu)要更大(da)的(de)(de)(de)功率，結果是(shi)電(dian)(dian)池(chi)越來越大(da)。同時(shi)，客戶希望可(ke)方(fang)便(bian)地用幾乎任何可(ke)用的(de)(de)(de)電(dian)(dian)源給這(zhe)(zhe)些電(dian)(dian)池(chi)充電(dian)(dian)。盡管便(bian)攜式電(dian)(dian)源領域的(de)(de)(de)這(zhe)(zhe)些趨勢造(zao)成(cheng)了(le)設計(ji)(ji)挑戰，但是(shi)LTC4155和LTC4000讓設計(ji)(ji)工作變得簡單多(duo)(duo)了(le)。在(zai)低(di)壓系統中，LTC4155高效率地提(ti)供高達(da)3.5A的(de)(de)(de)充電(dian)(dian)電(dian)(dian)流，而且(qie)提(ti)供很多(duo)(duo)高性(xing)能(neng)功能(neng)。LTC4000可(ke)構成(cheng)強大(da)的(de)(de)(de)充電(dian)(dian)解決方(fang)案(an)，而且(qie)幾乎可(ke)使用任何輸入，從而提(ti)供了(le)無與倫比的(de)(de)(de)性(xing)能(neng)和靈活性(xing)。