便攜式電(dian)(dian)源(yuan)的(de)(de)應用(yong)范圍很廣，也很多(duo)樣(yang)化。產(chan)品包括(kuo)消耗uW級平(ping)均功率的(de)(de)無線(xian)傳感器節點(dian)以及可(ke)用(yong)小車推著的(de)(de)、電(dian)(dian)池(chi)組(zu)耗電(dian)(dian)數(shu)百瓦-時(shi)的(de)(de)醫療或(huo)數(shu)據(ju)采(cai)集系統。不(bu)過，盡管應用(yong)種(zhong)(zhong)類很多(duo)，仍(reng)然出現(xian)了幾(ji)個趨勢，設計(ji)師日益需(xu)(xu)要給產(chan)品提(ti)(ti)供更大的(de)(de)功率，以支持不(bu)斷增多(duo)的(de)(de)功能，同(tong)時(shi)也在考慮怎樣(yang)用(yong)任何可(ke)用(yong)電(dian)(dian)源(yuan)給電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)。要滿(man)(man)足(zu)第一(yi)種(zhong)(zhong)需(xu)(xu)求(qiu)，就要提(ti)(ti)高電(dian)(dian)池(chi)容量。不(bu)幸的(de)(de)是，用(yong)戶大多(duo)比較(jiao)心急，容量提(ti)(ti)高以后，還必須在一(yi)個合理(li)的(de)(de)時(shi)間內(nei)充(chong)(chong)滿(man)(man)電(dian)(dian)，這就導致要增大充(chong)(chong)電(dian)(dian)電(dian)(dian)流。要滿(man)(man)足(zu)第二種(zhong)(zhong)需(xu)(xu)求(qiu)，就要求(qiu)電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)解(jie)決方案(an)提(ti)(ti)供極大的(de)(de)靈(ling)活性。本文(wen)將更詳(xiang)細地討論這些問(wen)題。

　　更大的功率

　　考(kao)慮(lv)一(yi)(yi)(yi)下新式(shi)手(shou)持式(shi)設(she)備(bei)，面向消費(fei)者(zhe)的(de)(de)(de)(de)(de)設(she)備(bei)和(he)工業設(she)備(bei)都(dou)可能包(bao)括蜂(feng)窩(wo)電(dian)(dian)話調(diao)制解調(diao)器、Wi-Fi模塊(kuai)、藍牙模塊(kuai)、大(da)(da)尺寸背光照明顯(xian)示屏(ping)…等等。很(hen)多(duo)手(shou)持式(shi)設(she)備(bei)的(de)(de)(de)(de)(de)電(dian)(dian)源架(jia)構都(dou)與蜂(feng)窩(wo)電(dian)(dian)話的(de)(de)(de)(de)(de)非常相似。一(yi)(yi)(yi)般情況下，用(yong)(yong)一(yi)(yi)(yi)個3.7V的(de)(de)(de)(de)(de)鋰離子(zi)電(dian)(dian)池(chi)作為(wei)(wei)主電(dian)(dian)源，因為(wei)(wei)鋰離子(zi)電(dian)(dian)池(chi)按重(zhong)量和(he)按體積的(de)(de)(de)(de)(de)能量密度都(dou)很(hen)高(單位分(fen)別(bie)為(wei)(wei)Wh/kg和(he)Wh/m3)。過(guo)去，很(hen)多(duo)大(da)(da)功率設(she)備(bei)都(dou)采用(yong)(yong)7.4V鋰離子(zi)電(dian)(dian)池(chi)，以降低(di)電(dian)(dian)流要求，不過(guo)低(di)價5V電(dian)(dian)源管理IC的(de)(de)(de)(de)(de)上(shang)市已經促使(shi)越(yue)來越(yue)多(duo)的(de)(de)(de)(de)(de)手(shou)持式(shi)設(she)備(bei)采用(yong)(yong)了(le)電(dian)(dian)壓更(geng)低(di)的(de)(de)(de)(de)(de)架(jia)構。平板(ban)電(dian)(dian)腦很(hen)好地說明了(le)這一(yi)(yi)(yi)點：一(yi)(yi)(yi)個典型的(de)(de)(de)(de)(de)平板(ban)電(dian)(dian)腦有極多(duo)的(de)(de)(de)(de)(de)功能以及非常大(da)(da)的(de)(de)(de)(de)(de)顯(xian)示屏(ping)(就便攜式(shi)設(she)備(bei)而言)。用(yong)(yong)3.7V電(dian)(dian)池(chi)供電(dian)(dian)時，其容量必(bi)須以數千(qian)毫(hao)安-小(xiao)時計算。為(wei)(wei)了(le)在幾個小(xiao)時內給(gei)這樣一(yi)(yi)(yi)個電(dian)(dian)池(chi)充(chong)滿電(dian)(dian)，需要數千(qian)mA的(de)(de)(de)(de)(de)充(chong)電(dian)(dian)電(dian)(dian)流。

　　然而，如果(guo)沒有大(da)電(dian)(dian)流(liu)(liu)交流(liu)(liu)適(shi)配(pei)器(qi)，盡管(guan)充(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)這(zhe)么高，也不能(neng)(neng)(neng)防止(zhi)消費者用USB端口給(gei)大(da)功率設備(bei)充(chong)電(dian)(dian)的(de)想法。為了滿(man)足這(zhe)種(zhong)需求(qiu)，當交流(liu)(liu)適(shi)配(pei)器(qi)可用時，電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)器(qi)必(bi)(bi)須(xu)能(neng)(neng)(neng)以大(da)電(dian)(dian)流(liu)(liu)(>2A)充(chong)電(dian)(dian)，而在沒有交流(liu)(liu)適(shi)配(pei)器(qi)可用時，電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)器(qi)必(bi)(bi)須(xu)仍能(neng)(neng)(neng)高效地(di)利用USB端口提供2.5W至(zhi)4.5W功率。此外，器(qi)件必(bi)(bi)須(xu)保護敏(min)感(gan)的(de)下游低(di)(di)壓(ya)組件免受可能(neng)(neng)(neng)出現過壓(ya)情況所導致的(de)損壞，同時必(bi)(bi)須(xu)無縫地(di)將大(da)電(dian)(dian)流(liu)(liu)從(cong)USB輸入、交流(liu)(liu)適(shi)配(pei)器(qi)或電(dian)(dian)池(chi)(chi)傳送(song)到負(fu)載(zai)，并(bing)最大(da)限度地(di)降低(di)(di)功耗。另(ling)外，該IC還必(bi)(bi)須(xu)安(an)全(quan)地(di)管(guan)理(li)電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)算法，并(bing)監(jian)視關鍵的(de)系統(tong)參數。

　　戰(zhan)勝單節電池供(gong)電的便(bian)攜(xie)式產品在功率方(fang)面的挑戰(zhan)

　　盡管看似(si)不(bu)(bu)可能找到能滿足上述要求的(de)單個IC，不(bu)(bu)過看一(yi)下LTC4155，這(zhe)是一(yi)個大功(gong)率(lv)(lv)、I2C控制的(de)高效(xiao)率(lv)(lv)電源(yuan)通路(lu)(PowerPath?)管理器(qi)(qi)、理想二(er)極管控制器(qi)(qi)和(he)鋰離(li)子電池充(chong)電器(qi)(qi)。該(gai)IC用(yong)來(lai)從各種(zhong)5V電源(yuan)高效(xiao)地傳送(song)高達3A的(de)電流，可產生超過3.5A的(de)可用(yong)電流，以(yi)供(gong)電池充(chong)電和(he)系統使(shi)用(yong)(參(can)見圖1)。LTC4155的(de)效(xiao)率(lv)(lv)為88%至94%，因此即(ji)使(shi)電流值這(zhe)么大，該(gai)IC仍然可以(yi)減輕熱(re)量預算限制(參(can)見圖2)。LTC4155的(de)開關式電源(yuan)通路(lu)拓撲(pu)無縫地管理從兩種(zhong)輸入電源(yuan)(例如一(yi)個交(jiao)流適配器(qi)(qi)和(he)一(yi)個USB端(duan)口(kou))到設備中可再充(chong)電鋰離(li)子電池的(de)配電，同時當(dang)輸入功(gong)率(lv)(lv)有限時，優先為系統負載(zai)供(gong)電。

圖1：LTC4155的典型應(ying)用電路(lu)

圖(tu)2：LTC4155的(de)典型效(xiao)率(lv)

　　與典型的(de)線(xian)性模式充電(dian)(dian)(dian)器相(xiang)比(bi)，LTC4155中開(kai)關穩壓器的(de)作用(yong)就像(xiang)一(yi)個變壓器，允許VOUT上(shang)的(de)負載(zai)電(dian)(dian)(dian)流(liu)超(chao)過輸(shu)入電(dian)(dian)(dian)源吸(xi)取的(de)電(dian)(dian)(dian)流(liu)，并極大地(di)提高(gao)電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)的(de)可用(yong)功率。前述例(li)子說明了LTC4155怎樣才能以高(gao)達3.5A的(de)電(dian)(dian)(dian)流(liu)高(gao)效(xiao)率地(di)充電(dian)(dian)(dian)，以實現更快的(de)充電(dian)(dian)(dian)時間。與普通的(de)開(kai)關型電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)器不同(tong)，LTC4155可即時接通工作，以確保即使電(dian)(dian)(dian)池(chi)沒電(dian)(dian)(dian)或已深度放電(dian)(dian)(dian)，當一(yi)插上(shang)電(dian)(dian)(dian)源插頭，系(xi)統電(dian)(dian)(dian)源也立即可用(yong)。

　　盡管是以(yi)很高的(de)(de)(de)速(su)率給電(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)，監視(shi)電(dian)(dian)(dian)池(chi)(chi)是否安(an)全也是很重要的(de)(de)(de)。當電(dian)(dian)(dian)池(chi)(chi)溫度降至低于0°C或升至高于40°C[由一(yi)個(ge)外(wai)部(bu)負(fu)溫度系數(NTC)熱敏電(dian)(dian)(dian)阻測量]時，LTC4155將自(zi)動停(ting)止充(chong)(chong)(chong)電(dian)(dian)(dian)。除(chu)了這種自(zi)主式功(gong)能，LTC4155還提供一(yi)個(ge)7位擴展標度模數轉換器(ADC)，以(yi)大約1°C的(de)(de)(de)分辨率監視(shi)電(dian)(dian)(dian)池(chi)(chi)溫度(參(can)見圖(tu)3)。結(jie)合(he)4個(ge)可用(yong)的(de)(de)(de)浮置電(dian)(dian)(dian)壓設定(ding)值和15個(ge)電(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流設定(ding)值，該ADC可基于電(dian)(dian)(dian)池(chi)(chi)溫度來建立定(ding)制的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)算法。

圖(tu)3：7位熱(re)敏電阻(zu)器ADC顯示(shi)LTC4155的預置(zhi)溫度(du)跳(tiao)變點

　　通過一個簡單的兩線I2C端口可獲得NTCADC的結果，從而能調節充電電流和電壓的設定值。該I2C端口通過控制16個輸入電流的設定值(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指示額外的狀態信息，例如輸入電源狀態、充電器狀(zhuang)態和故障狀(zhuang)態。由于(yu)支持USBOTG，因此無需任(ren)何額外的組件，就(jiu)可以反過來向USB端口提供5V電源。

　　LTC4155的(de)雙(shuang)路(lu)輸(shu)(shu)入(ru)(ru)、優先(xian)級多(duo)路(lu)復用器可根據用戶定義的(de)優先(xian)級(默認的(de)優先(xian)級為適(shi)配器輸(shu)(shu)入(ru)(ru))自主地(di)選擇最合適(shi)的(de)輸(shu)(shu)入(ru)(ru)(即墻上適(shi)配器或USB)。過壓(ya)保護(hu)(OVP)電路(lu)同時保護(hu)兩個輸(shu)(shu)入(ru)(ru)，以(yi)免這些(xie)輸(shu)(shu)入(ru)(ru)因(yin)無意(yi)間加上的(de)高壓(ya)或反向(xiang)電壓(ya)而(er)損壞。LTC4155的(de)理想二極管控制器保證即使輸(shu)(shu)入(ru)(ru)功率(lv)不足或未提供輸(shu)(shu)入(ru)(ru)功率(lv)時，也始終可向(xiang)VOUT提供足夠的(de)功率(lv)。

　　就平板電(dian)腦、工業條(tiao)碼掃(sao)描器(qi)等很多便(bian)攜(xie)式應用(yong)(yong)而(er)言，能(neng)管理兩個輸入(例(li)如USB和交流(liu)適配器(qi))就足夠了。不(bu)過，便(bian)攜(xie)式設備的(de)(de)設計(ji)師一直在尋求用(yong)(yong)任(ren)何可(ke)用(yong)(yong)電(dian)源都能(neng)給電(dian)池充(chong)電(dian)的(de)(de)方法

　　多種輸入源

　　用(yong)(yong)(yong)戶要用(yong)(yong)(yong)多種輸(shu)(shu)入源給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)有幾個原(yuan)因。有些(xie)應(ying)用(yong)(yong)(yong)也許需要擺(bai)脫電(dian)(dian)(dian)(dian)(dian)(dian)網的(de)(de)(de)(de)(de)(de)束(shu)縛，而靠太(tai)陽能電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)板(ban)供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)。另一(yi)(yi)(yi)些(xie)應(ying)用(yong)(yong)(yong)則(ze)可能要求(qiu)能方(fang)便地用(yong)(yong)(yong)交流適(shi)配器(qi)(qi)(qi)、汽車電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)或(huo)高(gao)(gao)壓(ya)工(gong)業及(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)源充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。無論出于(yu)(yu)何種原(yuan)因，這要求(qiu)都給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)系統增(zeng)加了極大(da)(da)的(de)(de)(de)(de)(de)(de)負(fu)擔。大(da)(da)多數電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)都利用(yong)(yong)(yong)降壓(ya)型(開關或(huo)線性)架構，用(yong)(yong)(yong)高(gao)(gao)于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)最高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)源給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。以(yi)前的(de)(de)(de)(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)產品輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)一(yi)(yi)(yi)般限制(zhi)為大(da)(da)約30V。這樣的(de)(de)(de)(de)(de)(de)限制(zhi)使設計師無法將電(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)源或(huo)者具42V開路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)(de)(de)(de)太(tai)陽能電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)板(ban)作(zuo)為可行的(de)(de)(de)(de)(de)(de)輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)源。在有些(xie)情況下，希望使用(yong)(yong)(yong)的(de)(de)(de)(de)(de)(de)輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)涵蓋了高(gao)(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)(de)(de)(de)(de)(de)范(fan)圍。設計一(yi)(yi)(yi)款應(ying)對此類(lei)難題的(de)(de)(de)(de)(de)(de)解決方(fang)案通常需要混合使用(yong)(yong)(yong)高(gao)(gao)精度的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流檢測(ce)放大(da)(da)器(qi)(qi)(qi)、ADC、一(yi)(yi)(yi)個用(yong)(yong)(yong)于(yu)(yu)控制(zhi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)(de)(de)微處(chu)理(li)器(qi)(qi)(qi)、一(yi)(yi)(yi)個高(gao)(gao)性能DC/DC轉(zhuan)換器(qi)(qi)(qi)以(yi)及(ji)(ji)一(yi)(yi)(yi)個理(li)想二極管或(huo)多路(lu)復用(yong)(yong)(yong)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。

　　強大的充電解(jie)決方案提(ti)供無與倫比的靈(ling)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驅動的典型DC/DC轉換器拓撲包括但不限于：降壓、升壓、降壓-升壓、SEPIC和反激式拓撲。該器件提供精確的輸入和充電電流調節，在3V至60V的寬輸入和輸出電壓范圍內工作，實現了與各種不同的輸入電壓源、以及不同尺寸和化學組成的電池組的兼容性。由于該器件的通用型配置，因此其典型應用十分廣泛，包括高功率電池充電器系統(tong)、高性能便攜式儀(yi)器(qi)、電池(chi)后備系統(tong)、配有工業電池(chi)的設備以(yi)及筆(bi)(bi)記本/小(xiao)型筆(bi)(bi)記本電腦(nao)。

　　除了可以(yi)(yi)與(yu)很多不同的(de)DC/DC拓撲(pu)結合(he)，LTC4000的(de)高壓能(neng)力還允許該器件構成強大和幾乎可使(shi)用(yong)(yong)任何輸(shu)入電(dian)源(yuan)(yuan)(參見圖4和圖5)的(de)電(dian)池(chi)充電(dian)解決方(fang)案。為了確(que)保來自(zi)這些輸(shu)入的(de)功率傳送給合(he)適的(de)負(fu)載，LTC4000采用(yong)(yong)了一種(zhong)智能(neng)電(dian)源(yuan)(yuan)通路(lu)拓撲(pu)，當(dang)輸(shu)入功率有(you)限時，該拓撲(pu)可優先為系統(tong)負(fu)載供電(dian)。LTC4000控制外(wai)(wai)部PFET，以(yi)(yi)提(ti)供低(di)損耗反向電(dian)流(liu)保護、電(dian)池(chi)的(de)低(di)損耗充電(dian)和放電(dian)以(yi)(yi)及即時接(jie)通工作，這樣就(jiu)可以(yi)(yi)確(que)保即使(shi)在電(dian)池(chi)沒電(dian)或(huo)深度放電(dian)時，當(dang)一插上電(dian)源(yuan)(yuan)，系統(tong)電(dian)源(yuan)(yuan)就(jiu)能(neng)立(li)即可用(yong)(yong)。外(wai)(wai)部檢(jian)測電(dian)阻器提(ti)供輸(shu)入電(dian)流(liu)和電(dian)池(chi)充電(dian)電(dian)流(liu)信(xin)息，從而使(shi)LTC4000能(neng)與(yu)涵蓋mW至kW功率范圍的(de)轉換(huan)器一起使(shi)用(yong)(yong)。

圖4：LTC4000和LTC3789：6V至36V_IN、4節5A鋰離子電池充電器

圖(tu)5：圖(tu)4電路中系統負載為4A時效(xiao)率隨VIN的變化

　　LTC4000的全功能電池充電控制器可為各種化學組成的電池充電，包括鋰離子/聚合物/磷酸、密封鉛酸(SLA)和鎳化學組成。該電池充電器還(huan)提(ti)供精確的電(dian)流檢(jian)測(ce)功能，從而(er)在大(da)電(dian)流應用情況下允(yun)許(xu)較低的檢(jian)測(ce)電(dian)壓(ya)。

　　結論

　　新式(shi)便攜(xie)式(shi)產品設計(ji)師(shi)的工作(zuo)極(ji)富挑戰(zhan)性，尤其是(shi)涉(she)及到電(dian)(dian)(dian)(dian)源(yuan)時(shi)。客戶不斷要(yao)求更多(duo)功能(neng)以導致需(xu)要(yao)更大的功率，結果是(shi)電(dian)(dian)(dian)(dian)池越來越大。同(tong)時(shi)，客戶希望可方便地(di)用幾乎(hu)任何(he)可用的電(dian)(dian)(dian)(dian)源(yuan)給這些(xie)電(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)。盡管(guan)便攜(xie)式(shi)電(dian)(dian)(dian)(dian)源(yuan)領域(yu)的這些(xie)趨勢造成了設計(ji)挑戰(zhan)，但是(shi)LTC4155和LTC4000讓設計(ji)工作(zuo)變得簡單多(duo)了。在低壓系統(tong)中，LTC4155高效(xiao)率地(di)提(ti)供(gong)(gong)高達(da)3.5A的充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流，而且提(ti)供(gong)(gong)很(hen)多(duo)高性能(neng)功能(neng)。LTC4000可構成強大的充電(dian)(dian)(dian)(dian)解決方案，而且幾乎(hu)可使(shi)用任何(he)輸入，從而提(ti)供(gong)(gong)了無與倫(lun)比的性能(neng)和靈(ling)活(huo)性。