背景

　　便攜式(shi)電(dian)源的(de)應用范圍(wei)很(hen)廣，也很(hen)多樣化。產品(pin)包(bao)括消耗uW級平均功(gong)率的(de)無線傳感器節(jie)點以(yi)及(ji)可用小車推著的(de)、電(dian)池組耗電(dian)數(shu)百瓦-時(shi)的(de)醫(yi)療或數(shu)據采(cai)集系統(tong)。不(bu)過(guo)，盡管應用種類很(hen)多，仍然出現了幾個趨勢，設(she)計師日(ri)益需要(yao)給(gei)產品(pin)提(ti)供更大(da)的(de)功(gong)率，以(yi)支持不(bu)斷增多的(de)功(gong)能，同時(shi)也在考慮怎樣用任何(he)可用電(dian)源給(gei)電(dian)池充(chong)(chong)電(dian)。要(yao)滿(man)足(zu)第一種需求，就要(yao)提(ti)高電(dian)池容量。不(bu)幸的(de)是，用戶(hu)大(da)多比較心急，容量提(ti)高以(yi)后，還必須在一個合(he)理的(de)時(shi)間內充(chong)(chong)滿(man)電(dian)，這就導(dao)致要(yao)增大(da)充(chong)(chong)電(dian)電(dian)流。要(yao)滿(man)足(zu)第二種需求，就要(yao)求電(dian)池充(chong)(chong)電(dian)解決方案提(ti)供極大(da)的(de)靈活(huo)性。本文將更詳細地討論這些問題。

　　更大的功率

　　考慮一下新式(shi)(shi)手(shou)持式(shi)(shi)設(she)(she)備(bei)(bei)，面(mian)向消費(fei)者的(de)(de)設(she)(she)備(bei)(bei)和(he)工業(ye)設(she)(she)備(bei)(bei)都可(ke)能(neng)(neng)包括蜂窩(wo)電(dian)(dian)(dian)話(hua)調制解調器、Wi-Fi模塊、藍牙模塊、大尺寸(cun)背光(guang)照(zhao)明顯示(shi)(shi)屏…等等。很多(duo)手(shou)持式(shi)(shi)設(she)(she)備(bei)(bei)的(de)(de)電(dian)(dian)(dian)源(yuan)架(jia)構都與蜂窩(wo)電(dian)(dian)(dian)話(hua)的(de)(de)非常(chang)相(xiang)似。一般情況下，用一個(ge)(ge)3.7V的(de)(de)鋰(li)離子(zi)電(dian)(dian)(dian)池(chi)(chi)作為主電(dian)(dian)(dian)源(yuan)，因(yin)為鋰(li)離子(zi)電(dian)(dian)(dian)池(chi)(chi)按重(zhong)量(liang)和(he)按體積的(de)(de)能(neng)(neng)量(liang)密度都很高(gao)(單位分別為Wh/kg和(he)Wh/m3)。過去，很多(duo)大功率(lv)設(she)(she)備(bei)(bei)都采用7.4V鋰(li)離子(zi)電(dian)(dian)(dian)池(chi)(chi)，以降(jiang)低電(dian)(dian)(dian)流要求，不過低價(jia)5V電(dian)(dian)(dian)源(yuan)管理IC的(de)(de)上(shang)市已經促使(shi)越來越多(duo)的(de)(de)手(shou)持式(shi)(shi)設(she)(she)備(bei)(bei)采用了(le)電(dian)(dian)(dian)壓(ya)更低的(de)(de)架(jia)構。平板電(dian)(dian)(dian)腦很好地說(shuo)明了(le)這(zhe)一點：一個(ge)(ge)典型的(de)(de)平板電(dian)(dian)(dian)腦有極多(duo)的(de)(de)功能(neng)(neng)以及非常(chang)大的(de)(de)顯示(shi)(shi)屏(就便攜式(shi)(shi)設(she)(she)備(bei)(bei)而言(yan))。用3.7V電(dian)(dian)(dian)池(chi)(chi)供電(dian)(dian)(dian)時(shi)，其容量(liang)必須(xu)以數千毫(hao)安-小時(shi)計算。為了(le)在幾個(ge)(ge)小時(shi)內(nei)給這(zhe)樣一個(ge)(ge)電(dian)(dian)(dian)池(chi)(chi)充滿(man)電(dian)(dian)(dian)，需要數千mA的(de)(de)充電(dian)(dian)(dian)電(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，電池充電器必須(xu)(xu)(xu)仍能高效地(di)(di)(di)利用USB端口提供2.5W至4.5W功(gong)率(lv)。此(ci)外，器件必須(xu)(xu)(xu)保護敏感的下(xia)游低壓組件免受可能出現過壓情況所導致的損壞，同(tong)時必須(xu)(xu)(xu)無縫地(di)(di)(di)將大(da)電流從USB輸(shu)入(ru)、交(jiao)流適配器或(huo)電池傳送到負(fu)載，并最(zui)大(da)限度地(di)(di)(di)降低功(gong)耗。另外，該(gai)IC還必須(xu)(xu)(xu)安全地(di)(di)(di)管理電池充(chong)電算法，并監視(shi)關鍵的系統參(can)數。

　　戰勝單(dan)節(jie)電池供電的便(bian)攜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)源高效地傳送(song)高達(da)3A的(de)電(dian)流(liu)，可產生(sheng)超過3.5A的(de)可用電(dian)流(liu)，以(yi)供(gong)電(dian)池充電(dian)和系(xi)統使(shi)(shi)用(參(can)見圖1)。LTC4155的(de)效率為(wei)88%至94%，因此即使(shi)(shi)電(dian)流(liu)值這么大，該IC仍然(ran)可以(yi)減輕熱量預算限制(參(can)見圖2)。LTC4155的(de)開(kai)關式電(dian)源通路拓(tuo)撲無縫地管理從兩(liang)種輸(shu)入(ru)電(dian)源(例(li)如一個交流(liu)適配器和一個USB端口)到設備中可再充電(dian)鋰(li)離子電(dian)池的(de)配電(dian)，同時當輸(shu)入(ru)功率有限時，優先(xian)為(wei)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，LTC4155可即時(shi)接通工作(zuo)，以確保即使電(dian)池(chi)沒電(dian)或已深度放電(dian)，當一插上電(dian)源(yuan)插頭，系統電(dian)源(yuan)也立即可用。

　　盡管是以很高的(de)速率(lv)給電(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)，監視(shi)電(dian)(dian)(dian)(dian)池(chi)是否安全也(ye)是很重要的(de)。當電(dian)(dian)(dian)(dian)池(chi)溫度(du)降至(zhi)低(di)于0°C或升(sheng)至(zhi)高于40°C[由(you)一(yi)個外部負溫度(du)系(xi)數(NTC)熱敏電(dian)(dian)(dian)(dian)阻測量]時，LTC4155將自動停止充電(dian)(dian)(dian)(dian)。除(chu)了(le)這種自主式功能，LTC4155還提供一(yi)個7位擴(kuo)展(zhan)標度(du)模數轉換器(ADC)，以大約1°C的(de)分辨率(lv)監視(shi)電(dian)(dian)(dian)(dian)池(chi)溫度(du)(參見圖3)。結合4個可(ke)用(yong)的(de)浮(fu)置電(dian)(dian)(dian)(dian)壓設定(ding)值和15個電(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流設定(ding)值，該ADC可(ke)基于電(dian)(dian)(dian)(dian)池(chi)溫度(du)來建立(li)定(ding)制(zhi)的(de)充電(dian)(dian)(dian)(dian)算(suan)法。

　通過一個簡單(dan)的(de)兩線(xian)(xian)I2C端(duan)口(kou)可(ke)獲得(de)NTCADC的(de)結果，從(cong)而(er)能(neng)調節充(chong)電(dian)(dian)電(dian)(dian)流和電(dian)(dian)壓的(de)設(she)定(ding)值。該I2C端(duan)口(kou)通過控制16個輸入電(dian)(dian)流的(de)設(she)定(ding)值(包(bao)括(kuo)USB2.0和3.0兼容設(she)置)，還可(ke)提供(gong)USB兼容性。該通信總線(xian)(xian)允許LTC4155指示額(e)外(wai)的(de)狀(zhuang)(zhuang)態(tai)信息(xi)，例如輸入電(dian)(dian)源狀(zhuang)(zhuang)態(tai)、充(chong)電(dian)(dian)器狀(zhuang)(zhuang)態(tai)和故障狀(zhuang)(zhuang)態(tai)。由(you)于支持USBOTG，因(yin)此(ci)無需任何(he)額(e)外(wai)的(de)組件，就可(ke)以反過來向(xiang)USB端(duan)口(kou)提供(gong)5V電(dian)(dian)源。

　　LTC4155的(de)(de)雙路(lu)輸(shu)(shu)入、優(you)先級多路(lu)復用(yong)器(qi)可根據(ju)用(yong)戶定(ding)義的(de)(de)優(you)先級(默(mo)認的(de)(de)優(you)先級為適(shi)配器(qi)輸(shu)(shu)入)自主地選(xuan)擇(ze)最合適(shi)的(de)(de)輸(shu)(shu)入(即(ji)墻上(shang)適(shi)配器(qi)或(huo)USB)。過壓(ya)保護(OVP)電路(lu)同時保護兩個輸(shu)(shu)入，以(yi)免這些輸(shu)(shu)入因無意間(jian)加上(shang)的(de)(de)高(gao)壓(ya)或(huo)反向電壓(ya)而損壞(huai)。LTC4155的(de)(de)理想二極管控制器(qi)保證(zheng)即(ji)使輸(shu)(shu)入功率不足(zu)或(huo)未提(ti)供輸(shu)(shu)入功率時，也始(shi)終可向VOUT提(ti)供足(zu)夠的(de)(de)功率。

　　就平(ping)板電腦、工(gong)業條碼掃描(miao)器等很多(duo)便攜式應用而言(yan)，能(neng)管理兩個輸(shu)入(例(li)如USB和(he)交流適配器)就足夠(gou)了。不過，便攜式設備的(de)設計(ji)師一直在(zai)尋求用任(ren)何(he)可用電源都能(neng)給電池(chi)充電的(de)方法

　　多種輸入源

　　用(yong)(yong)(yong)(yong)戶要用(yong)(yong)(yong)(yong)多種(zhong)輸(shu)入(ru)源(yuan)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)有(you)幾個(ge)原因。有(you)些應用(yong)(yong)(yong)(yong)也許需要擺脫電(dian)(dian)(dian)(dian)(dian)(dian)(dian)網的(de)(de)束縛，而(er)靠太陽能(neng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池板供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。另一些應用(yong)(yong)(yong)(yong)則可(ke)能(neng)要求(qiu)能(neng)方便地(di)用(yong)(yong)(yong)(yong)交流(liu)適(shi)配器(qi)(qi)(qi)、汽車電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池或高壓工(gong)業及(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。無論出于何(he)種(zhong)原因，這(zhe)要求(qiu)都給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)系統增加(jia)了(le)極大的(de)(de)負擔。大多數電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)都利用(yong)(yong)(yong)(yong)降(jiang)壓型(開(kai)關(guan)或線性)架構，用(yong)(yong)(yong)(yong)高于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池最(zui)高電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓源(yuan)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。以前的(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)產品輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓一般限制(zhi)為大約30V。這(zhe)樣的(de)(de)限制(zhi)使(shi)設(she)(she)計(ji)師(shi)無法將(jiang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)或者具(ju)42V開(kai)路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)(de)太陽能(neng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池板作為可(ke)行的(de)(de)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)。在有(you)些情況下，希望使(shi)用(yong)(yong)(yong)(yong)的(de)(de)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓涵蓋了(le)高于和低于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)(de)范(fan)圍。設(she)(she)計(ji)一款應對此類難題的(de)(de)解決方案通常需要混合使(shi)用(yong)(yong)(yong)(yong)高精度的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)檢測放(fang)大器(qi)(qi)(qi)、ADC、一個(ge)用(yong)(yong)(yong)(yong)于控制(zhi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)微(wei)處理器(qi)(qi)(qi)、一個(ge)高性能(neng)DC/DC轉換器(qi)(qi)(qi)以及(ji)一個(ge)理想二(er)極管或多路(lu)復用(yong)(yong)(yong)(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。

　　強大的充電解決(jue)方案提供無(wu)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(ke)由LTC4000驅動(dong)的(de)典(dian)型(xing)DC/DC轉換器(qi)拓撲包括(kuo)但不限于(yu)：降壓(ya)、升壓(ya)、降壓(ya)-升壓(ya)、SEPIC和(he)反激式拓撲。該器(qi)件提供(gong)精確的(de)輸入(ru)和(he)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)調節，在3V至60V的(de)寬(kuan)輸入(ru)和(he)輸出電(dian)(dian)(dian)(dian)壓(ya)范圍內工作，實現(xian)了與各種不同(tong)(tong)的(de)輸入(ru)電(dian)(dian)(dian)(dian)壓(ya)源、以及不同(tong)(tong)尺寸和(he)化學(xue)組(zu)(zu)成的(de)電(dian)(dian)(dian)(dian)池(chi)組(zu)(zu)的(de)兼容(rong)性(xing)。由于(yu)該器(qi)件的(de)通用型(xing)配(pei)置，因此其典(dian)型(xing)應(ying)用十分廣泛，包括(kuo)高(gao)功(gong)率電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)器(qi)系統、高(gao)性(xing)能便(bian)攜式儀器(qi)、電(dian)(dian)(dian)(dian)池(chi)后備系統、配(pei)有工業電(dian)(dian)(dian)(dian)池(chi)的(de)設備以及筆記(ji)本(ben)/小型(xing)筆記(ji)本(ben)電(dian)(dian)(dian)(dian)腦(nao)。

　　除了可(ke)(ke)(ke)以與很多不同的DC/DC拓(tuo)撲結(jie)合，LTC4000的高(gao)壓(ya)能力還允許該器(qi)件構成強(qiang)大和幾乎(hu)可(ke)(ke)(ke)使(shi)用(yong)任何輸(shu)入(ru)電(dian)(dian)(dian)源(參見圖4和圖5)的電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)解決方(fang)案。為了確保來自這(zhe)些(xie)輸(shu)入(ru)的功率傳送(song)給(gei)合適的負載，LTC4000采用(yong)了一(yi)種(zhong)智(zhi)能電(dian)(dian)(dian)源通路拓(tuo)撲，當輸(shu)入(ru)功率有(you)限時(shi)，該拓(tuo)撲可(ke)(ke)(ke)優(you)先為系(xi)統負載供電(dian)(dian)(dian)。LTC4000控制外部PFET，以提供低(di)損耗反向(xiang)電(dian)(dian)(dian)流(liu)保護、電(dian)(dian)(dian)池(chi)的低(di)損耗充電(dian)(dian)(dian)和放電(dian)(dian)(dian)以及即(ji)時(shi)接通工作，這(zhe)樣就可(ke)(ke)(ke)以確保即(ji)使(shi)在電(dian)(dian)(dian)池(chi)沒(mei)電(dian)(dian)(dian)或(huo)深度放電(dian)(dian)(dian)時(shi)，當一(yi)插(cha)上電(dian)(dian)(dian)源，系(xi)統電(dian)(dian)(dian)源就能立即(ji)可(ke)(ke)(ke)用(yong)。外部檢測電(dian)(dian)(dian)阻器(qi)提供輸(shu)入(ru)電(dian)(dian)(dian)流(liu)和電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)信息(xi)，從而使(shi)LTC4000能與涵蓋mW至kW功率范(fan)圍的轉換器(qi)一(yi)起(qi)使(shi)用(yong)。

　　LTC4000的(de)全(quan)功能(neng)電(dian)(dian)池(chi)充電(dian)(dian)控(kong)制器可為各種化學組成的(de)電(dian)(dian)池(chi)充電(dian)(dian)，包括鋰離子(zi)/聚合物/磷酸、密(mi)封鉛(qian)酸(SLA)和鎳(nie)化學組成。該電(dian)(dian)池(chi)充電(dian)(dian)器還(huan)提供精確的(de)電(dian)(dian)流檢測(ce)(ce)功能(neng)，從而在大電(dian)(dian)流應(ying)用情(qing)況下允許(xu)較低(di)的(de)檢測(ce)(ce)電(dian)(dian)壓。

　　結論

　　新式(shi)便攜式(shi)產(chan)品(pin)設計(ji)師的(de)(de)工作極富(fu)挑戰性，尤其是(shi)涉及(ji)到電(dian)(dian)(dian)源時。客戶不斷(duan)要求更(geng)多功能(neng)(neng)以導致需要更(geng)大(da)的(de)(de)功率，結果是(shi)電(dian)(dian)(dian)池越(yue)來越(yue)大(da)。同時，客戶希望可(ke)方便地(di)(di)用(yong)幾乎任何可(ke)用(yong)的(de)(de)電(dian)(dian)(dian)源給這些電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)。盡(jin)管便攜式(shi)電(dian)(dian)(dian)源領域(yu)的(de)(de)這些趨勢(shi)造(zao)成(cheng)了(le)設計(ji)挑戰，但是(shi)LTC4155和LTC4000讓(rang)設計(ji)工作變得簡單多了(le)。在低(di)壓系統中(zhong)，LTC4155高(gao)效率地(di)(di)提(ti)供高(gao)達3.5A的(de)(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)，而且提(ti)供很多高(gao)性能(neng)(neng)功能(neng)(neng)。LTC4000可(ke)構成(cheng)強大(da)的(de)(de)充(chong)電(dian)(dian)(dian)解決方案，而且幾乎可(ke)使用(yong)任何輸入，從而提(ti)供了(le)無與倫(lun)比的(de)(de)性能(neng)(neng)和靈活性。