背景

　　便攜式電(dian)(dian)(dian)源(yuan)的(de)應用(yong)范(fan)圍(wei)很(hen)廣，也很(hen)多(duo)樣(yang)化。產品包括消耗uW級(ji)平均功率(lv)的(de)無(wu)線傳感器節點以及可用(yong)小車推著的(de)、電(dian)(dian)(dian)池組(zu)耗電(dian)(dian)(dian)數(shu)百瓦(wa)-時的(de)醫療或數(shu)據采集系統。不(bu)過，盡管應用(yong)種(zhong)類很(hen)多(duo)，仍然出現了幾(ji)個趨勢(shi)，設計(ji)師日益需要(yao)給(gei)產品提(ti)供更大(da)的(de)功率(lv)，以支持不(bu)斷(duan)增多(duo)的(de)功能，同(tong)時也在考慮(lv)怎樣(yang)用(yong)任何可用(yong)電(dian)(dian)(dian)源(yuan)給(gei)電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)。要(yao)滿(man)足第(di)一(yi)種(zhong)需求(qiu)，就要(yao)提(ti)高電(dian)(dian)(dian)池容(rong)量。不(bu)幸(xing)的(de)是，用(yong)戶大(da)多(duo)比較心急，容(rong)量提(ti)高以后，還必須在一(yi)個合理(li)的(de)時間內充(chong)滿(man)電(dian)(dian)(dian)，這就導致要(yao)增大(da)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流。要(yao)滿(man)足第(di)二種(zhong)需求(qiu)，就要(yao)求(qiu)電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)解決方(fang)案提(ti)供極大(da)的(de)靈活性(xing)。本文將更詳細地討論(lun)這些問題。

　　更大的功率

　　考慮一下新(xin)式手(shou)持(chi)式設(she)備(bei)(bei)，面向消費者的(de)(de)(de)設(she)備(bei)(bei)和(he)(he)工業設(she)備(bei)(bei)都可能(neng)包括蜂(feng)窩電(dian)(dian)(dian)(dian)(dian)(dian)話調(diao)制解(jie)調(diao)器、Wi-Fi模塊(kuai)、藍(lan)牙(ya)模塊(kuai)、大尺寸背光照明顯(xian)示(shi)屏…等等。很(hen)多手(shou)持(chi)式設(she)備(bei)(bei)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)架(jia)構(gou)都與蜂(feng)窩電(dian)(dian)(dian)(dian)(dian)(dian)話的(de)(de)(de)非(fei)常(chang)相似(si)。一般情況(kuang)下，用(yong)(yong)一個3.7V的(de)(de)(de)鋰離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)作為主電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)，因為鋰離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)按重量(liang)(liang)和(he)(he)按體積(ji)的(de)(de)(de)能(neng)量(liang)(liang)密(mi)度都很(hen)高(單位分別為Wh/kg和(he)(he)Wh/m3)。過(guo)去，很(hen)多大功率設(she)備(bei)(bei)都采(cai)用(yong)(yong)7.4V鋰離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)，以(yi)降低電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)要求，不(bu)過(guo)低價5V電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)管理(li)IC的(de)(de)(de)上(shang)市已(yi)經促使越來越多的(de)(de)(de)手(shou)持(chi)式設(she)備(bei)(bei)采(cai)用(yong)(yong)了電(dian)(dian)(dian)(dian)(dian)(dian)壓更低的(de)(de)(de)架(jia)構(gou)。平(ping)板電(dian)(dian)(dian)(dian)(dian)(dian)腦很(hen)好(hao)地說明了這(zhe)(zhe)一點：一個典(dian)型的(de)(de)(de)平(ping)板電(dian)(dian)(dian)(dian)(dian)(dian)腦有極多的(de)(de)(de)功能(neng)以(yi)及(ji)非(fei)常(chang)大的(de)(de)(de)顯(xian)示(shi)屏(就便攜式設(she)備(bei)(bei)而言(yan))。用(yong)(yong)3.7V電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)供電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)，其容量(liang)(liang)必須以(yi)數千毫安-小時(shi)計算。為了在幾(ji)個小時(shi)內給這(zhe)(zhe)樣一個電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充滿電(dian)(dian)(dian)(dian)(dian)(dian)，需要數千mA的(de)(de)(de)充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(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，電池充電器必須仍能(neng)高效地(di)利(li)用USB端口(kou)提供2.5W至4.5W功(gong)率。此(ci)外，器(qi)件必須保護敏(min)感的下游低壓組件免(mian)受可能(neng)出現過壓情況(kuang)所(suo)導致的損壞，同(tong)時(shi)必須無縫地(di)將大(da)電(dian)流從USB輸(shu)入、交流適配器(qi)或電(dian)池(chi)傳送到負載，并(bing)最大(da)限度地(di)降低功(gong)耗(hao)。另外，該IC還必須安(an)全(quan)地(di)管理電(dian)池(chi)充電(dian)算法，并(bing)監(jian)視關鍵的系統參(can)數。

　　戰勝單(dan)節電池供電的(de)便攜(xie)式產品在功率方面的(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5V電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)高(gao)(gao)效地(di)傳送高(gao)(gao)達3A的電(dian)(dian)(dian)(dian)(dian)流(liu)，可(ke)產生(sheng)超過3.5A的可(ke)用電(dian)(dian)(dian)(dian)(dian)流(liu)，以供(gong)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)和(he)(he)系統(tong)使(shi)用(參(can)見(jian)圖(tu)1)。LTC4155的效率(lv)為88%至94%，因(yin)此即使(shi)電(dian)(dian)(dian)(dian)(dian)流(liu)值這么大(da)，該IC仍(reng)然(ran)可(ke)以減輕(qing)熱量預算(suan)限(xian)制(參(can)見(jian)圖(tu)2)。LTC4155的開關式電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)通路拓撲無縫地(di)管(guan)理(li)從兩種輸入電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(例如一個(ge)交流(liu)適(shi)配(pei)器(qi)和(he)(he)一個(ge)USB端口)到(dao)設備中可(ke)再充(chong)電(dian)(dian)(dian)(dian)(dian)鋰離子電(dian)(dian)(dian)(dian)(dian)池(chi)的配(pei)電(dian)(dian)(dian)(dian)(dian)，同(tong)時(shi)當輸入功率(lv)有限(xian)時(shi)，優先為系統(tong)負載供(gong)電(dian)(dian)(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)時接通(tong)工作，以(yi)確保即(ji)使電(dian)池(chi)沒電(dian)或已深度放電(dian)，當一插上電(dian)源插頭，系統(tong)電(dian)源也立即(ji)可用。

　　盡(jin)管是以(yi)很(hen)(hen)高的速率(lv)給(gei)電(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)，監(jian)(jian)視(shi)電(dian)(dian)池(chi)(chi)是否安全也是很(hen)(hen)重要的。當電(dian)(dian)池(chi)(chi)溫(wen)度降(jiang)至(zhi)低于(yu)0°C或升至(zhi)高于(yu)40°C[由一個(ge)外部負溫(wen)度系數(NTC)熱敏(min)電(dian)(dian)阻(zu)測量]時，LTC4155將自動(dong)停止充(chong)(chong)電(dian)(dian)。除了這(zhe)種自主式功能，LTC4155還提供一個(ge)7位擴展標度模數轉換器(ADC)，以(yi)大約1°C的分辨率(lv)監(jian)(jian)視(shi)電(dian)(dian)池(chi)(chi)溫(wen)度(參(can)見圖3)。結合4個(ge)可用的浮置(zhi)電(dian)(dian)壓設定(ding)值(zhi)和15個(ge)電(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)電(dian)(dian)流設定(ding)值(zhi)，該(gai)ADC可基于(yu)電(dian)(dian)池(chi)(chi)溫(wen)度來(lai)建立定(ding)制的充(chong)(chong)電(dian)(dian)算法。

　通過(guo)一個(ge)簡單(dan)的(de)(de)兩線I2C端口可獲得(de)NTCADC的(de)(de)結(jie)果，從而能調節(jie)充電電流和電壓(ya)的(de)(de)設定值。該I2C端口通過(guo)控(kong)制16個(ge)輸入(ru)電流的(de)(de)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(wai)(wai)的(de)(de)狀態(tai)(tai)(tai)信息(xi)，例如輸入(ru)電源狀態(tai)(tai)(tai)、充電器狀態(tai)(tai)(tai)和故(gu)障狀態(tai)(tai)(tai)。由于支持USBOTG，因此無需任何額外(wai)(wai)的(de)(de)組(zu)件，就(jiu)可以反過(guo)來向(xiang)USB端口提供5V電源。

　　LTC4155的雙路(lu)(lu)輸入、優先級多路(lu)(lu)復(fu)用器(qi)可(ke)根(gen)據(ju)用戶定義的優先級(默(mo)認的優先級為適(shi)配器(qi)輸入)自主地選擇最合適(shi)的輸入(即(ji)墻上適(shi)配器(qi)或(huo)USB)。過(guo)壓保護(OVP)電路(lu)(lu)同(tong)時保護兩個(ge)輸入，以(yi)免這(zhe)些輸入因無意(yi)間加上的高(gao)壓或(huo)反向電壓而損壞。LTC4155的理想二極管控(kong)制器(qi)保證即(ji)使輸入功(gong)(gong)率不足或(huo)未(wei)提(ti)供輸入功(gong)(gong)率時，也始(shi)終(zhong)可(ke)向VOUT提(ti)供足夠的功(gong)(gong)率。

　　就平板電腦、工業(ye)條碼掃描器等很多便攜式應用(yong)而(er)言，能(neng)管(guan)理兩個輸入(例如USB和交流適配器)就足夠了。不過(guo)，便攜式設(she)備的(de)設(she)計(ji)師一直在尋求用(yong)任何可用(yong)電源都能(neng)給電池充電的(de)方法

　　多種輸入源

　　用(yong)(yong)(yong)戶要(yao)用(yong)(yong)(yong)多(duo)種輸(shu)(shu)入(ru)源給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)(dian)有(you)幾個(ge)(ge)原因。有(you)些(xie)應用(yong)(yong)(yong)也許需(xu)要(yao)擺脫電(dian)(dian)(dian)(dian)(dian)(dian)網的(de)束縛，而靠太(tai)(tai)陽能電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)板供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)。另一(yi)(yi)些(xie)應用(yong)(yong)(yong)則可能要(yao)求(qiu)能方便地(di)用(yong)(yong)(yong)交(jiao)流(liu)(liu)適配器(qi)、汽車電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)或高(gao)壓(ya)工業及(ji)電(dian)(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)源充電(dian)(dian)(dian)(dian)(dian)(dian)。無論出于(yu)(yu)何(he)種原因，這要(yao)求(qiu)都(dou)給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)(dian)系統增加了(le)極大(da)的(de)負擔。大(da)多(duo)數電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)都(dou)利用(yong)(yong)(yong)降壓(ya)型(xing)(開(kai)關或線性)架構(gou)，用(yong)(yong)(yong)高(gao)于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)最(zui)高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)源給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)(dian)。以(yi)(yi)前的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)產(chan)品輸(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)一(yi)(yi)般限制(zhi)為大(da)約30V。這樣(yang)的(de)限制(zhi)使設(she)計師無法將電(dian)(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)源或者具42V開(kai)路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)太(tai)(tai)陽能電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)板作為可行的(de)輸(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)源。在有(you)些(xie)情(qing)況下，希望使用(yong)(yong)(yong)的(de)輸(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)涵蓋了(le)高(gao)于(yu)(yu)和低于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)范圍(wei)。設(she)計一(yi)(yi)款應對此類難題的(de)解(jie)決方案通常需(xu)要(yao)混合使用(yong)(yong)(yong)高(gao)精(jing)度的(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)檢測放大(da)器(qi)、ADC、一(yi)(yi)個(ge)(ge)用(yong)(yong)(yong)于(yu)(yu)控制(zhi)充電(dian)(dian)(dian)(dian)(dian)(dian)的(de)微處理器(qi)、一(yi)(yi)個(ge)(ge)高(gao)性能DC/DC轉換器(qi)以(yi)(yi)及(ji)一(yi)(yi)個(ge)(ge)理想(xiang)二極管或多(duo)路(lu)復用(yong)(yong)(yong)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。

　　強大的(de)(de)充電解決方案提供無與(yu)倫比的(de)(de)靈活(huo)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(ke)由LTC4000驅動的(de)典型(xing)DC/DC轉換器(qi)拓撲包括但不(bu)限(xian)于：降壓、升壓、降壓-升壓、SEPIC和(he)反激(ji)式(shi)拓撲。該器(qi)件(jian)提供精確的(de)輸入和(he)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)調節，在3V至60V的(de)寬輸入和(he)輸出電(dian)(dian)(dian)壓范圍內工(gong)作，實現了與各種不(bu)同(tong)的(de)輸入電(dian)(dian)(dian)壓源、以及(ji)不(bu)同(tong)尺寸和(he)化學組成的(de)電(dian)(dian)(dian)池(chi)組的(de)兼容(rong)性(xing)。由于該器(qi)件(jian)的(de)通用(yong)型(xing)配置，因此其典型(xing)應用(yong)十分廣(guang)泛，包括高功率電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)器(qi)系統、高性(xing)能便攜式(shi)儀(yi)器(qi)、電(dian)(dian)(dian)池(chi)后備系統、配有工(gong)業(ye)電(dian)(dian)(dian)池(chi)的(de)設備以及(ji)筆記本/小型(xing)筆記本電(dian)(dian)(dian)腦。

　　除了(le)可(ke)以與(yu)很多不(bu)同的(de)(de)(de)DC/DC拓(tuo)撲結(jie)合(he)，LTC4000的(de)(de)(de)高(gao)壓能(neng)力還(huan)允許該器(qi)件(jian)構成強(qiang)大和幾乎(hu)可(ke)使(shi)用任何輸(shu)入(ru)電(dian)(dian)(dian)(dian)源(yuan)(參見圖4和圖5)的(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)解決方案。為了(le)確保來自(zi)這些輸(shu)入(ru)的(de)(de)(de)功(gong)率(lv)傳送給(gei)合(he)適的(de)(de)(de)負載，LTC4000采用了(le)一(yi)種智能(neng)電(dian)(dian)(dian)(dian)源(yuan)通(tong)路拓(tuo)撲，當輸(shu)入(ru)功(gong)率(lv)有限時，該拓(tuo)撲可(ke)優先為系(xi)(xi)統(tong)負載供電(dian)(dian)(dian)(dian)。LTC4000控制外部(bu)PFET，以提(ti)供低損(sun)耗(hao)反向(xiang)電(dian)(dian)(dian)(dian)流(liu)保護、電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)低損(sun)耗(hao)充(chong)電(dian)(dian)(dian)(dian)和放(fang)電(dian)(dian)(dian)(dian)以及(ji)即(ji)時接(jie)通(tong)工(gong)作(zuo)，這樣(yang)就可(ke)以確保即(ji)使(shi)在電(dian)(dian)(dian)(dian)池(chi)(chi)沒電(dian)(dian)(dian)(dian)或深(shen)度放(fang)電(dian)(dian)(dian)(dian)時，當一(yi)插上電(dian)(dian)(dian)(dian)源(yuan)，系(xi)(xi)統(tong)電(dian)(dian)(dian)(dian)源(yuan)就能(neng)立即(ji)可(ke)用。外部(bu)檢測電(dian)(dian)(dian)(dian)阻器(qi)提(ti)供輸(shu)入(ru)電(dian)(dian)(dian)(dian)流(liu)和電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)信(xin)息，從(cong)而(er)使(shi)LTC4000能(neng)與(yu)涵蓋(gai)mW至kW功(gong)率(lv)范圍(wei)的(de)(de)(de)轉換器(qi)一(yi)起使(shi)用。

　　LTC4000的全功(gong)能電(dian)(dian)池充(chong)電(dian)(dian)控制(zhi)器可為(wei)各種化學組(zu)成(cheng)的電(dian)(dian)池充(chong)電(dian)(dian)，包括鋰離子/聚合物/磷酸(suan)、密封鉛酸(suan)(SLA)和(he)鎳化學組(zu)成(cheng)。該(gai)電(dian)(dian)池充(chong)電(dian)(dian)器還(huan)提供精確的電(dian)(dian)流(liu)檢(jian)測功(gong)能，從而在大電(dian)(dian)流(liu)應(ying)用情況(kuang)下(xia)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)師的(de)工(gong)作極(ji)富挑(tiao)戰性(xing)，尤(you)其是涉及到電(dian)(dian)源時(shi)。客戶不斷要求(qiu)更(geng)多功(gong)能(neng)以導(dao)致需要更(geng)大的(de)功(gong)率，結果(guo)是電(dian)(dian)池越(yue)來越(yue)大。同時(shi)，客戶希望可(ke)方(fang)便(bian)地用幾乎(hu)任(ren)何可(ke)用的(de)電(dian)(dian)源給這(zhe)些(xie)電(dian)(dian)池充電(dian)(dian)。盡管便(bian)攜式電(dian)(dian)源領域的(de)這(zhe)些(xie)趨(qu)勢造成(cheng)了設(she)計(ji)挑(tiao)戰，但是LTC4155和LTC4000讓設(she)計(ji)工(gong)作變得簡(jian)單多了。在(zai)低壓系統中，LTC4155高(gao)效(xiao)率地提(ti)供(gong)高(gao)達3.5A的(de)充電(dian)(dian)電(dian)(dian)流，而(er)且提(ti)供(gong)很多高(gao)性(xing)能(neng)功(gong)能(neng)。LTC4000可(ke)構成(cheng)強大的(de)充電(dian)(dian)解決方(fang)案，而(er)且幾乎(hu)可(ke)使用任(ren)何輸入，從而(er)提(ti)供(gong)了無與倫比的(de)性(xing)能(neng)和靈活性(xing)。