背景

　　便攜(xie)式電(dian)源的(de)(de)應用范圍很(hen)廣(guang)，也很(hen)多樣(yang)化。產品包括消耗(hao)uW級平均功(gong)率的(de)(de)無線傳(chuan)感器節(jie)點以及可(ke)用小車推著的(de)(de)、電(dian)池(chi)組耗(hao)電(dian)數百瓦-時(shi)的(de)(de)醫(yi)療或(huo)數據采集系統(tong)。不(bu)(bu)過，盡管應用種類很(hen)多，仍然出現了幾個趨勢，設計師日益需要(yao)給產品提供更(geng)大的(de)(de)功(gong)率，以支(zhi)持不(bu)(bu)斷增多的(de)(de)功(gong)能，同時(shi)也在(zai)考慮怎樣(yang)用任何(he)可(ke)用電(dian)源給電(dian)池(chi)充電(dian)。要(yao)滿足第一種需求(qiu)，就要(yao)提高電(dian)池(chi)容量。不(bu)(bu)幸的(de)(de)是(shi)，用戶大多比較(jiao)心急(ji)，容量提高以后，還(huan)必須在(zai)一個合理的(de)(de)時(shi)間內充滿電(dian)，這(zhe)(zhe)就導致要(yao)增大充電(dian)電(dian)流。要(yao)滿足第二種需求(qiu)，就要(yao)求(qiu)電(dian)池(chi)充電(dian)解決(jue)方(fang)案(an)提供極大的(de)(de)靈活性(xing)。本文將更(geng)詳細(xi)地討論這(zhe)(zhe)些(xie)問題(ti)。

　　更大的功率

　　考慮一(yi)下(xia)新式(shi)(shi)手持式(shi)(shi)設(she)(she)(she)(she)備(bei)，面向消(xiao)費者(zhe)的(de)設(she)(she)(she)(she)備(bei)和(he)工業設(she)(she)(she)(she)備(bei)都可能(neng)(neng)包括(kuo)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)、大尺寸(cun)背光照明(ming)顯(xian)示屏(ping)…等(deng)等(deng)。很多(duo)(duo)手持式(shi)(shi)設(she)(she)(she)(she)備(bei)的(de)電(dian)(dian)源(yuan)架(jia)構都與(yu)蜂(feng)窩(wo)電(dian)(dian)話的(de)非(fei)常(chang)相似。一(yi)般情(qing)況(kuang)下(xia)，用(yong)(yong)(yong)一(yi)個(ge)3.7V的(de)鋰離(li)子電(dian)(dian)池作為主(zhu)電(dian)(dian)源(yuan)，因為鋰離(li)子電(dian)(dian)池按(an)重量(liang)和(he)按(an)體(ti)積的(de)能(neng)(neng)量(liang)密度都很高(單位分別為Wh/kg和(he)Wh/m3)。過去，很多(duo)(duo)大功(gong)率設(she)(she)(she)(she)備(bei)都采用(yong)(yong)(yong)7.4V鋰離(li)子電(dian)(dian)池，以(yi)降低電(dian)(dian)流(liu)要求，不過低價5V電(dian)(dian)源(yuan)管(guan)理IC的(de)上(shang)市已經促使越來越多(duo)(duo)的(de)手持式(shi)(shi)設(she)(she)(she)(she)備(bei)采用(yong)(yong)(yong)了(le)電(dian)(dian)壓更低的(de)架(jia)構。平(ping)板(ban)(ban)電(dian)(dian)腦(nao)很好(hao)地(di)說明(ming)了(le)這一(yi)點：一(yi)個(ge)典(dian)型(xing)的(de)平(ping)板(ban)(ban)電(dian)(dian)腦(nao)有極多(duo)(duo)的(de)功(gong)能(neng)(neng)以(yi)及非(fei)常(chang)大的(de)顯(xian)示屏(ping)(就便攜(xie)式(shi)(shi)設(she)(she)(she)(she)備(bei)而(er)言)。用(yong)(yong)(yong)3.7V電(dian)(dian)池供電(dian)(dian)時(shi)(shi)，其容量(liang)必須以(yi)數(shu)千(qian)毫安(an)-小(xiao)時(shi)(shi)計算。為了(le)在幾(ji)個(ge)小(xiao)時(shi)(shi)內(nei)給這樣一(yi)個(ge)電(dian)(dian)池充(chong)滿電(dian)(dian)，需要數(shu)千(qian)mA的(de)充(chong)電(dian)(dian)電(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(bi)(bi)須(xu)仍(reng)能(neng)高(gao)效地(di)利用USB端口(kou)提(ti)供(gong)2.5W至4.5W功率。此外(wai)(wai)，器件必(bi)(bi)須(xu)保(bao)護(hu)敏感的下游低(di)壓組件免受可能(neng)出現過壓情況(kuang)所導致的損壞，同時必(bi)(bi)須(xu)無縫地(di)將大電(dian)流從USB輸入、交流適配器或電(dian)池(chi)傳(chuan)送到負載(zai)，并最大限度地(di)降低(di)功耗。另(ling)外(wai)(wai)，該IC還必(bi)(bi)須(xu)安(an)全地(di)管(guan)理電(dian)池(chi)充(chong)電(dian)算(suan)法，并監(jian)視關鍵的系統(tong)參數。

　　戰(zhan)勝(sheng)單節電(dian)池(chi)供電(dian)的便攜式(shi)產(chan)品在功率方面的挑戰(zhan)

　　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(zhong)(zhong)5V電(dian)(dian)源高(gao)效地傳(chuan)送高(gao)達3A的(de)電(dian)(dian)流(liu)(liu)，可(ke)(ke)產生超過3.5A的(de)可(ke)(ke)用電(dian)(dian)流(liu)(liu)，以供電(dian)(dian)池充(chong)電(dian)(dian)和系統使用(參(can)見圖1)。LTC4155的(de)效率為88%至94%，因此即使電(dian)(dian)流(liu)(liu)值這么(me)大，該IC仍然(ran)可(ke)(ke)以減輕熱量預算限制(zhi)(參(can)見圖2)。LTC4155的(de)開(kai)關式電(dian)(dian)源通路(lu)拓(tuo)撲無縫地管(guan)理從兩種(zhong)(zhong)輸(shu)入電(dian)(dian)源(例(li)如(ru)一(yi)個交流(liu)(liu)適配(pei)器和一(yi)個USB端(duan)口)到設備中可(ke)(ke)再(zai)充(chong)電(dian)(dian)鋰離(li)子電(dian)(dian)池的(de)配(pei)電(dian)(dian)，同(tong)時當輸(shu)入功率有(you)限時，優(you)先為系統負載供電(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(ke)即時(shi)接通工(gong)作，以確(que)保即使電池沒電或已深度放電，當一插上電源插頭，系統電源也立即可(ke)用。

　　盡管(guan)是(shi)以很(hen)高(gao)(gao)的(de)速率(lv)給電(dian)池(chi)充(chong)電(dian)，監視電(dian)池(chi)是(shi)否安全(quan)也是(shi)很(hen)重要的(de)。當(dang)電(dian)池(chi)溫(wen)度(du)降至低于(yu)(yu)0°C或升至高(gao)(gao)于(yu)(yu)40°C[由一個外部負溫(wen)度(du)系(xi)數(NTC)熱敏(min)電(dian)阻測量]時，LTC4155將自動停止充(chong)電(dian)。除(chu)了這種自主式功能，LTC4155還提供一個7位擴展標(biao)度(du)模數轉換器(ADC)，以大約(yue)1°C的(de)分辨率(lv)監視電(dian)池(chi)溫(wen)度(du)(參見圖3)。結合4個可用(yong)的(de)浮置電(dian)壓設定(ding)值(zhi)和15個電(dian)池(chi)充(chong)電(dian)電(dian)流設定(ding)值(zhi)，該(gai)ADC可基于(yu)(yu)電(dian)池(chi)溫(wen)度(du)來建(jian)立定(ding)制(zhi)的(de)充(chong)電(dian)算法。

　通過(guo)一(yi)個(ge)簡單的(de)兩線I2C端(duan)口(kou)可獲得NTCADC的(de)結果，從而能調節充(chong)電(dian)(dian)電(dian)(dian)流(liu)和(he)電(dian)(dian)壓(ya)的(de)設定值。該I2C端(duan)口(kou)通過(guo)控制16個(ge)輸(shu)入(ru)電(dian)(dian)流(liu)的(de)設定值(包括USB2.0和(he)3.0兼(jian)容(rong)設置)，還可提供(gong)USB兼(jian)容(rong)性。該通信總線允許LTC4155指示額(e)(e)外的(de)狀(zhuang)態(tai)信息，例如輸(shu)入(ru)電(dian)(dian)源狀(zhuang)態(tai)、充(chong)電(dian)(dian)器狀(zhuang)態(tai)和(he)故(gu)障狀(zhuang)態(tai)。由于支持(chi)USBOTG，因此無需任(ren)何額(e)(e)外的(de)組件，就可以反過(guo)來向USB端(duan)口(kou)提供(gong)5V電(dian)(dian)源。

　　LTC4155的(de)雙路輸(shu)(shu)入(ru)(ru)、優(you)(you)先(xian)級(ji)多路復用(yong)器(qi)可(ke)根據用(yong)戶定義(yi)的(de)優(you)(you)先(xian)級(ji)(默認(ren)的(de)優(you)(you)先(xian)級(ji)為(wei)適(shi)配器(qi)輸(shu)(shu)入(ru)(ru))自主地選擇最合適(shi)的(de)輸(shu)(shu)入(ru)(ru)(即墻上(shang)(shang)適(shi)配器(qi)或(huo)(huo)USB)。過壓保(bao)護(OVP)電路同(tong)時保(bao)護兩個輸(shu)(shu)入(ru)(ru)，以(yi)免這些輸(shu)(shu)入(ru)(ru)因無意間加(jia)上(shang)(shang)的(de)高壓或(huo)(huo)反向電壓而損壞。LTC4155的(de)理想二極管(guan)控制器(qi)保(bao)證即使輸(shu)(shu)入(ru)(ru)功(gong)率(lv)(lv)(lv)不足或(huo)(huo)未提供輸(shu)(shu)入(ru)(ru)功(gong)率(lv)(lv)(lv)時，也始終可(ke)向VOUT提供足夠的(de)功(gong)率(lv)(lv)(lv)。

　　就(jiu)平板電(dian)腦、工(gong)業條碼(ma)掃描器等很多便攜(xie)(xie)式應用(yong)而(er)言，能管理兩個輸(shu)入(例如USB和交流適配器)就(jiu)足(zu)夠了。不過，便攜(xie)(xie)式設(she)備的(de)設(she)計(ji)師一直在尋求(qiu)用(yong)任(ren)何可用(yong)電(dian)源都能給電(dian)池充電(dian)的(de)方法

　　多種輸入源

　　用(yong)戶要用(yong)多種(zhong)輸入源(yuan)(yuan)(yuan)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)有(you)幾個原(yuan)(yuan)因。有(you)些應(ying)(ying)用(yong)也許需要擺脫電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)網(wang)的(de)(de)(de)束(shu)縛，而(er)靠太陽(yang)能(neng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)板(ban)供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。另一些應(ying)(ying)用(yong)則可(ke)能(neng)要求能(neng)方便地用(yong)交流(liu)適配器(qi)(qi)、汽車電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)或(huo)高(gao)壓(ya)工業及電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。無論出于(yu)何(he)種(zhong)原(yuan)(yuan)因，這(zhe)要求都(dou)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)系統(tong)增加了極(ji)大的(de)(de)(de)負擔。大多數(shu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)都(dou)利用(yong)降壓(ya)型(開關或(huo)線性)架構，用(yong)高(gao)于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)最高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)源(yuan)(yuan)(yuan)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。以前的(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)產品輸入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)一般限制(zhi)為大約30V。這(zhe)樣的(de)(de)(de)限制(zhi)使(shi)設(she)計(ji)師無法(fa)將電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)或(huo)者(zhe)具42V開路(lu)(lu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)太陽(yang)能(neng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)板(ban)作(zuo)為可(ke)行的(de)(de)(de)輸入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)。在有(you)些情況下，希望使(shi)用(yong)的(de)(de)(de)輸入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)涵蓋了高(gao)于(yu)和(he)低于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)范圍(wei)。設(she)計(ji)一款應(ying)(ying)對此(ci)類(lei)難(nan)題的(de)(de)(de)解決方案(an)通(tong)常需要混合使(shi)用(yong)高(gao)精度(du)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)檢(jian)測放大器(qi)(qi)、ADC、一個用(yong)于(yu)控制(zhi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)微處(chu)理器(qi)(qi)、一個高(gao)性能(neng)DC/DC轉換器(qi)(qi)以及一個理想二極(ji)管或(huo)多路(lu)(lu)復用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。

　　強大的充電(dian)解決方案提供(gong)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(you)LTC4000驅(qu)動(dong)的典(dian)型DC/DC轉換器拓(tuo)撲包括(kuo)但不限于(yu)：降壓(ya)、升壓(ya)、降壓(ya)-升壓(ya)、SEPIC和反激(ji)式(shi)拓(tuo)撲。該(gai)器件(jian)提供精確的輸入(ru)(ru)和充電電流調(diao)節，在3V至(zhi)60V的寬輸入(ru)(ru)和輸出電壓(ya)范圍內工(gong)作，實現(xian)了與(yu)各(ge)種(zhong)不同的輸入(ru)(ru)電壓(ya)源、以(yi)及不同尺寸和化學(xue)組成的電池組的兼容性。由(you)于(yu)該(gai)器件(jian)的通用型配置(zhi)，因此其典(dian)型應用十分(fen)廣(guang)泛(fan)，包括(kuo)高(gao)功率電池充電器系(xi)統、高(gao)性能便攜式(shi)儀器、電池后(hou)備系(xi)統、配有工(gong)業電池的設備以(yi)及筆記(ji)本/小型筆記(ji)本電腦。

　　除了可以與很多不同(tong)的(de)DC/DC拓撲結合(he)，LTC4000的(de)高壓能(neng)力還(huan)允許(xu)該(gai)器(qi)件構成強大(da)和(he)幾乎可使(shi)(shi)(shi)用任(ren)何輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)源(參見圖4和(he)圖5)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)解決方案。為(wei)了確保(bao)來自這些(xie)輸(shu)(shu)入的(de)功(gong)率(lv)傳送給合(he)適的(de)負(fu)載，LTC4000采用了一種智(zhi)能(neng)電(dian)(dian)(dian)(dian)(dian)(dian)源通(tong)路拓撲，當(dang)輸(shu)(shu)入功(gong)率(lv)有限時，該(gai)拓撲可優(you)先為(wei)系統(tong)負(fu)載供(gong)(gong)電(dian)(dian)(dian)(dian)(dian)(dian)。LTC4000控制外部(bu)PFET，以提供(gong)(gong)低(di)損(sun)耗反(fan)向電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)保(bao)護、電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)低(di)損(sun)耗充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)和(he)放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)以及即時接(jie)通(tong)工作，這樣就可以確保(bao)即使(shi)(shi)(shi)在電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)沒電(dian)(dian)(dian)(dian)(dian)(dian)或深度放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)時，當(dang)一插上電(dian)(dian)(dian)(dian)(dian)(dian)源，系統(tong)電(dian)(dian)(dian)(dian)(dian)(dian)源就能(neng)立即可用。外部(bu)檢測電(dian)(dian)(dian)(dian)(dian)(dian)阻器(qi)提供(gong)(gong)輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)和(he)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)信息，從而(er)使(shi)(shi)(shi)LTC4000能(neng)與涵蓋mW至(zhi)kW功(gong)率(lv)范圍的(de)轉換器(qi)一起(qi)使(shi)(shi)(shi)用。

　　LTC4000的(de)全功(gong)能(neng)電(dian)池充電(dian)控制器(qi)可為各(ge)種化(hua)學組成(cheng)(cheng)的(de)電(dian)池充電(dian)，包括鋰離子/聚合物/磷(lin)酸(suan)、密(mi)封鉛酸(suan)(SLA)和(he)鎳化(hua)學組成(cheng)(cheng)。該(gai)電(dian)池充電(dian)器(qi)還提供(gong)精確(que)的(de)電(dian)流(liu)檢(jian)測(ce)功(gong)能(neng)，從而在大(da)電(dian)流(liu)應(ying)用情況下允許(xu)較低的(de)檢(jian)測(ce)電(dian)壓。

　　結論

　　新式便(bian)攜式產(chan)品(pin)設(she)計師的(de)(de)工(gong)作(zuo)極(ji)富(fu)挑(tiao)戰性(xing)，尤其(qi)是涉及到(dao)電(dian)(dian)源(yuan)(yuan)時(shi)。客戶不斷(duan)要求更多功(gong)能(neng)以(yi)導致需要更大的(de)(de)功(gong)率，結果(guo)是電(dian)(dian)池(chi)(chi)越來(lai)越大。同時(shi)，客戶希(xi)望可(ke)方(fang)便(bian)地(di)用(yong)(yong)幾乎任何(he)可(ke)用(yong)(yong)的(de)(de)電(dian)(dian)源(yuan)(yuan)給這些電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)。盡(jin)管便(bian)攜式電(dian)(dian)源(yuan)(yuan)領域的(de)(de)這些趨勢造成了設(she)計挑(tiao)戰，但是LTC4155和LTC4000讓設(she)計工(gong)作(zuo)變(bian)得簡單多了。在低壓(ya)系統(tong)中，LTC4155高效率地(di)提供高達3.5A的(de)(de)充(chong)電(dian)(dian)電(dian)(dian)流，而且(qie)提供很多高性(xing)能(neng)功(gong)能(neng)。LTC4000可(ke)構成強大的(de)(de)充(chong)電(dian)(dian)解決方(fang)案，而且(qie)幾乎可(ke)使用(yong)(yong)任何(he)輸入，從而提供了無與(yu)倫比(bi)的(de)(de)性(xing)能(neng)和靈(ling)活性(xing)。