背景

　　便攜(xie)式電(dian)(dian)(dian)源的(de)應用范圍很廣(guang)，也(ye)很多(duo)樣化(hua)。產(chan)品包括(kuo)消耗(hao)uW級平均功率(lv)的(de)無線傳感器節(jie)點以及可(ke)用小(xiao)車推著的(de)、電(dian)(dian)(dian)池組耗(hao)電(dian)(dian)(dian)數(shu)(shu)百(bai)瓦(wa)-時(shi)(shi)的(de)醫(yi)療或數(shu)(shu)據采集系(xi)統。不(bu)過，盡管(guan)應用種(zhong)類很多(duo)，仍然出現了幾(ji)個(ge)趨勢，設計師日益需(xu)要(yao)給(gei)產(chan)品提(ti)(ti)(ti)供更(geng)大的(de)功率(lv)，以支持不(bu)斷增多(duo)的(de)功能，同時(shi)(shi)也(ye)在(zai)考(kao)慮怎樣用任何(he)可(ke)用電(dian)(dian)(dian)源給(gei)電(dian)(dian)(dian)池充電(dian)(dian)(dian)。要(yao)滿足第一種(zhong)需(xu)求(qiu)，就(jiu)要(yao)提(ti)(ti)(ti)高電(dian)(dian)(dian)池容量(liang)。不(bu)幸的(de)是，用戶(hu)大多(duo)比較心急，容量(liang)提(ti)(ti)(ti)高以后，還必須在(zai)一個(ge)合理的(de)時(shi)(shi)間內充滿電(dian)(dian)(dian)，這就(jiu)導(dao)致要(yao)增大充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)。要(yao)滿足第二種(zhong)需(xu)求(qiu)，就(jiu)要(yao)求(qiu)電(dian)(dian)(dian)池充電(dian)(dian)(dian)解決方案提(ti)(ti)(ti)供極大的(de)靈活(huo)性。本(ben)文(wen)將(jiang)更(geng)詳細地討論這些問題(ti)。

　　更大的功率

　　考慮一(yi)(yi)下新式(shi)手持(chi)(chi)式(shi)設備(bei)(bei)，面向消費者(zhe)的(de)(de)設備(bei)(bei)和工(gong)業設備(bei)(bei)都可(ke)能包括蜂窩電(dian)(dian)(dian)(dian)(dian)(dian)話(hua)調制解調器、Wi-Fi模塊(kuai)、藍牙模塊(kuai)、大(da)尺寸背光(guang)照明(ming)顯示(shi)屏…等(deng)等(deng)。很(hen)(hen)多手持(chi)(chi)式(shi)設備(bei)(bei)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)源架(jia)構都與蜂窩電(dian)(dian)(dian)(dian)(dian)(dian)話(hua)的(de)(de)非(fei)常(chang)相似。一(yi)(yi)般情(qing)況下，用(yong)一(yi)(yi)個(ge)3.7V的(de)(de)鋰離(li)子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)池作為(wei)(wei)主電(dian)(dian)(dian)(dian)(dian)(dian)源，因為(wei)(wei)鋰離(li)子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)池按(an)重量和按(an)體積(ji)的(de)(de)能量密度都很(hen)(hen)高(單位分別為(wei)(wei)Wh/kg和Wh/m3)。過(guo)(guo)去，很(hen)(hen)多大(da)功率設備(bei)(bei)都采用(yong)7.4V鋰離(li)子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)池，以降低(di)電(dian)(dian)(dian)(dian)(dian)(dian)流要(yao)求(qiu)，不過(guo)(guo)低(di)價5V電(dian)(dian)(dian)(dian)(dian)(dian)源管理IC的(de)(de)上市已經促使越(yue)來越(yue)多的(de)(de)手持(chi)(chi)式(shi)設備(bei)(bei)采用(yong)了(le)電(dian)(dian)(dian)(dian)(dian)(dian)壓更低(di)的(de)(de)架(jia)構。平板電(dian)(dian)(dian)(dian)(dian)(dian)腦(nao)很(hen)(hen)好(hao)地(di)說明(ming)了(le)這一(yi)(yi)點：一(yi)(yi)個(ge)典型(xing)的(de)(de)平板電(dian)(dian)(dian)(dian)(dian)(dian)腦(nao)有極多的(de)(de)功能以及非(fei)常(chang)大(da)的(de)(de)顯示(shi)屏(就便攜式(shi)設備(bei)(bei)而言)。用(yong)3.7V電(dian)(dian)(dian)(dian)(dian)(dian)池供電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)，其容(rong)量必須以數千毫安(an)-小(xiao)時(shi)(shi)計算。為(wei)(wei)了(le)在幾個(ge)小(xiao)時(shi)(shi)內給這樣一(yi)(yi)個(ge)電(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)滿(man)電(dian)(dian)(dian)(dian)(dian)(dian)，需要(yao)數千mA的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流。

　　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)須仍(reng)能(neng)高效地利用USB端(duan)口提供2.5W至4.5W功率。此外(wai)，器件必(bi)須保護敏(min)感的下游(you)低壓組件免受可能(neng)出現(xian)過壓情況(kuang)所(suo)導致的損壞，同(tong)時必(bi)須無(wu)縫地將大電(dian)(dian)(dian)流從USB輸入、交(jiao)流適配器或電(dian)(dian)(dian)池傳送到負載，并最大限度(du)地降低功耗(hao)。另外(wai)，該IC還必(bi)須安全地管理電(dian)(dian)(dian)池充電(dian)(dian)(dian)算法，并監視(shi)關鍵的系(xi)統參數。

　　戰勝單節電池供電的便攜(xie)式產品在功率方面的挑戰

　　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)源高效地(di)傳送(song)高達3A的(de)電(dian)(dian)流，可(ke)產生超過3.5A的(de)可(ke)用電(dian)(dian)流，以(yi)供電(dian)(dian)池充(chong)電(dian)(dian)和系統(tong)使(shi)用(參見(jian)圖(tu)1)。LTC4155的(de)效率(lv)為88%至94%，因此即使(shi)電(dian)(dian)流值(zhi)這么大，該IC仍然可(ke)以(yi)減(jian)輕熱量預(yu)算限(xian)制(參見(jian)圖(tu)2)。LTC4155的(de)開關式電(dian)(dian)源通路拓撲無(wu)縫地(di)管理從兩種輸入(ru)電(dian)(dian)源(例如一(yi)(yi)個交流適(shi)配器和一(yi)(yi)個USB端口)到設備中可(ke)再充(chong)電(dian)(dian)鋰(li)離子電(dian)(dian)池的(de)配電(dian)(dian)，同時當輸入(ru)功率(lv)有限(xian)時，優先為系統(tong)負載供電(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(bu)同，LTC4155可即(ji)(ji)時(shi)接通(tong)工作，以確保即(ji)(ji)使電(dian)(dian)池沒電(dian)(dian)或已深度放(fang)電(dian)(dian)，當(dang)一插(cha)上電(dian)(dian)源(yuan)(yuan)插(cha)頭，系統電(dian)(dian)源(yuan)(yuan)也(ye)立即(ji)(ji)可用。

　　盡管(guan)是以(yi)很高的(de)速率給電(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)，監視(shi)電(dian)(dian)(dian)(dian)池是否安全(quan)也是很重要的(de)。當電(dian)(dian)(dian)(dian)池溫度(du)降至(zhi)低于(yu)0°C或升至(zhi)高于(yu)40°C[由一個(ge)外部負(fu)溫度(du)系(xi)數(shu)(NTC)熱敏(min)電(dian)(dian)(dian)(dian)阻測量]時(shi)，LTC4155將自(zi)動(dong)停止充電(dian)(dian)(dian)(dian)。除了這種自(zi)主(zhu)式(shi)功(gong)能，LTC4155還提供一個(ge)7位擴展標度(du)模數(shu)轉換(huan)器(ADC)，以(yi)大約1°C的(de)分(fen)辨率監視(shi)電(dian)(dian)(dian)(dian)池溫度(du)(參見(jian)圖3)。結合4個(ge)可用的(de)浮置電(dian)(dian)(dian)(dian)壓設定(ding)值(zhi)和15個(ge)電(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流設定(ding)值(zhi)，該ADC可基于(yu)電(dian)(dian)(dian)(dian)池溫度(du)來建立定(ding)制的(de)充電(dian)(dian)(dian)(dian)算法(fa)。

　通過一個(ge)簡單的兩線(xian)I2C端(duan)口(kou)可獲得NTCADC的結果(guo)，從(cong)而能調節充電(dian)(dian)電(dian)(dian)流和電(dian)(dian)壓(ya)的設定值。該I2C端(duan)口(kou)通過控(kong)制16個(ge)輸入電(dian)(dian)流的設定值(包括USB2.0和3.0兼(jian)(jian)容(rong)設置)，還可提供USB兼(jian)(jian)容(rong)性。該通信總線(xian)允許LTC4155指示額(e)外的狀態(tai)(tai)信息(xi)，例如輸入電(dian)(dian)源狀態(tai)(tai)、充電(dian)(dian)器狀態(tai)(tai)和故障狀態(tai)(tai)。由于支持(chi)USBOTG，因此無(wu)需任何額(e)外的組件(jian)，就可以反(fan)過來向USB端(duan)口(kou)提供5V電(dian)(dian)源。

　　LTC4155的(de)(de)(de)雙路(lu)輸(shu)(shu)入(ru)、優先級多路(lu)復(fu)用器可根據(ju)用戶定義的(de)(de)(de)優先級(默認(ren)的(de)(de)(de)優先級為適(shi)配器輸(shu)(shu)入(ru))自主(zhu)地選擇最合適(shi)的(de)(de)(de)輸(shu)(shu)入(ru)(即墻(qiang)上(shang)適(shi)配器或USB)。過壓保護(OVP)電路(lu)同(tong)時保護兩個(ge)輸(shu)(shu)入(ru)，以免這些輸(shu)(shu)入(ru)因無意(yi)間加上(shang)的(de)(de)(de)高壓或反向電壓而損壞。LTC4155的(de)(de)(de)理想(xiang)二極管控(kong)制器保證即使輸(shu)(shu)入(ru)功(gong)率不足或未提(ti)供輸(shu)(shu)入(ru)功(gong)率時，也始終可向VOUT提(ti)供足夠的(de)(de)(de)功(gong)率。

　　就(jiu)平板電腦、工業條碼掃描器等很多便攜(xie)式應用而(er)言，能管理兩個輸入(例如USB和交流適配器)就(jiu)足夠了。不過，便攜(xie)式設(she)備的設(she)計師一直在尋求用任何可(ke)用電源(yuan)都能給電池充電的方法(fa)

　　多種輸入源

　　用(yong)戶要用(yong)多種輸入(ru)(ru)源給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)有幾個(ge)原因。有些(xie)應(ying)(ying)用(yong)也許(xu)需要擺脫電(dian)(dian)(dian)(dian)(dian)(dian)(dian)網的(de)束縛，而靠(kao)太(tai)陽能電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)板(ban)供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。另一些(xie)應(ying)(ying)用(yong)則可能要求能方便(bian)地用(yong)交流適配器(qi)、汽車(che)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)或高壓(ya)(ya)工業及(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。無(wu)論出于(yu)(yu)何種原因，這要求都給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)系統增加了(le)極大的(de)負擔。大多數電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)都利用(yong)降壓(ya)(ya)型(開(kai)關或線(xian)性(xing))架構，用(yong)高于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)最高電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)源給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。以前(qian)的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)產品輸入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)一般限(xian)制為(wei)大約(yue)30V。這樣的(de)限(xian)制使設計師無(wu)法(fa)將電(dian)(dian)(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源或者具42V開(kai)路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)太(tai)陽能電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)板(ban)作(zuo)為(wei)可行的(de)輸入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源。在有些(xie)情(qing)況(kuang)下，希望使用(yong)的(de)輸入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)涵蓋了(le)高于(yu)(yu)和低于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)范圍。設計一款應(ying)(ying)對(dui)此(ci)類難題的(de)解決方案通常需要混合使用(yong)高精度(du)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流檢測放大器(qi)、ADC、一個(ge)用(yong)于(yu)(yu)控制充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)微處理器(qi)、一個(ge)高性(xing)能DC/DC轉(zhuan)換(huan)器(qi)以及(ji)一個(ge)理想二極管或多路(lu)復用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。

　　強大(da)的充(chong)電解(jie)決(jue)方案提供無與(yu)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(dong)的(de)典型(xing)(xing)DC/DC轉換器拓撲包(bao)括但(dan)不(bu)限于：降壓、升壓、降壓-升壓、SEPIC和反激(ji)式拓撲。該(gai)器件提供精確的(de)輸入和充(chong)電(dian)電(dian)流調(diao)節(jie)，在3V至60V的(de)寬輸入和輸出(chu)電(dian)壓范(fan)圍內工(gong)作，實現了與各(ge)種不(bu)同的(de)輸入電(dian)壓源、以(yi)及(ji)不(bu)同尺寸(cun)和化(hua)學(xue)組成的(de)電(dian)池組的(de)兼容性。由于該(gai)器件的(de)通用型(xing)(xing)配置，因此其典型(xing)(xing)應用十分廣泛，包(bao)括高功(gong)率電(dian)池充(chong)電(dian)器系統、高性能便(bian)攜式儀(yi)器、電(dian)池后備系統、配有工(gong)業電(dian)池的(de)設(she)備以(yi)及(ji)筆(bi)記(ji)本(ben)(ben)/小型(xing)(xing)筆(bi)記(ji)本(ben)(ben)電(dian)腦。

　　除(chu)了可以與(yu)很多不同的(de)(de)DC/DC拓撲結合，LTC4000的(de)(de)高(gao)壓能(neng)力還允許該(gai)器(qi)件(jian)構成(cheng)強大和幾乎可使用(yong)(yong)任(ren)何輸(shu)入(ru)(ru)電(dian)(dian)(dian)源(參見(jian)圖4和圖5)的(de)(de)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)解(jie)決(jue)方案。為了確保來自這些輸(shu)入(ru)(ru)的(de)(de)功率(lv)傳送(song)給合適的(de)(de)負載(zai)，LTC4000采用(yong)(yong)了一種智能(neng)電(dian)(dian)(dian)源通路拓撲，當輸(shu)入(ru)(ru)功率(lv)有限時，該(gai)拓撲可優先為系統負載(zai)供(gong)電(dian)(dian)(dian)。LTC4000控制外(wai)部PFET，以提供(gong)低損(sun)耗反(fan)向(xiang)電(dian)(dian)(dian)流保護、電(dian)(dian)(dian)池(chi)的(de)(de)低損(sun)耗充(chong)電(dian)(dian)(dian)和放電(dian)(dian)(dian)以及即時接通工作，這樣(yang)就可以確保即使在電(dian)(dian)(dian)池(chi)沒電(dian)(dian)(dian)或(huo)深度放電(dian)(dian)(dian)時，當一插上電(dian)(dian)(dian)源，系統電(dian)(dian)(dian)源就能(neng)立即可用(yong)(yong)。外(wai)部檢測(ce)電(dian)(dian)(dian)阻器(qi)提供(gong)輸(shu)入(ru)(ru)電(dian)(dian)(dian)流和電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流信息(xi)，從而使LTC4000能(neng)與(yu)涵蓋mW至kW功率(lv)范圍的(de)(de)轉換器(qi)一起使用(yong)(yong)。

　　LTC4000的全功能電(dian)池充電(dian)控制器(qi)可為(wei)各種化學組成的電(dian)池充電(dian)，包(bao)括鋰(li)離子/聚合物/磷酸、密封鉛酸(SLA)和鎳化學組成。該(gai)電(dian)池充電(dian)器(qi)還(huan)提供精確的電(dian)流檢測功能，從(cong)而在大電(dian)流應用情況下允(yun)許較低的檢測電(dian)壓。

　　結論

　　新式便攜(xie)式產品設(she)計(ji)(ji)師的(de)(de)工(gong)作(zuo)極富挑(tiao)戰性，尤其是(shi)涉及到電(dian)(dian)源(yuan)時(shi)。客(ke)戶(hu)不斷要求更(geng)多功能以導(dao)致(zhi)需(xu)要更(geng)大的(de)(de)功率(lv)，結(jie)果是(shi)電(dian)(dian)池越來越大。同時(shi)，客(ke)戶(hu)希望可(ke)(ke)方便地用(yong)幾乎(hu)任(ren)何(he)(he)可(ke)(ke)用(yong)的(de)(de)電(dian)(dian)源(yuan)給這(zhe)(zhe)些(xie)電(dian)(dian)池充(chong)電(dian)(dian)。盡管便攜(xie)式電(dian)(dian)源(yuan)領(ling)域的(de)(de)這(zhe)(zhe)些(xie)趨勢造成了(le)設(she)計(ji)(ji)挑(tiao)戰，但是(shi)LTC4155和LTC4000讓設(she)計(ji)(ji)工(gong)作(zuo)變得簡單(dan)多了(le)。在低壓(ya)系統中(zhong)，LTC4155高(gao)(gao)效率(lv)地提(ti)供高(gao)(gao)達3.5A的(de)(de)充(chong)電(dian)(dian)電(dian)(dian)流(liu)，而且提(ti)供很多高(gao)(gao)性能功能。LTC4000可(ke)(ke)構成強大的(de)(de)充(chong)電(dian)(dian)解決(jue)方案，而且幾乎(hu)可(ke)(ke)使用(yong)任(ren)何(he)(he)輸入(ru)，從而提(ti)供了(le)無與(yu)倫(lun)比的(de)(de)性能和靈活性。