便攜式(shi)電(dian)(dian)(dian)源的(de)(de)應(ying)(ying)用(yong)(yong)范圍很(hen)廣，也(ye)很(hen)多樣化(hua)。產品包(bao)括消耗uW級平均功(gong)率的(de)(de)無線傳感器節(jie)點以(yi)及可用(yong)(yong)小(xiao)車推著的(de)(de)、電(dian)(dian)(dian)池(chi)組耗電(dian)(dian)(dian)數百瓦(wa)-時的(de)(de)醫療(liao)或數據采集系統。不(bu)過(guo)，盡(jin)管應(ying)(ying)用(yong)(yong)種(zhong)類很(hen)多，仍(reng)然出現了幾個趨勢(shi)，設(she)計師日益需(xu)要(yao)(yao)給產品提供更大(da)(da)(da)的(de)(de)功(gong)率，以(yi)支持不(bu)斷增多的(de)(de)功(gong)能(neng)，同時也(ye)在考慮怎樣用(yong)(yong)任何可用(yong)(yong)電(dian)(dian)(dian)源給電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)。要(yao)(yao)滿(man)足(zu)第一種(zhong)需(xu)求(qiu)，就(jiu)要(yao)(yao)提高電(dian)(dian)(dian)池(chi)容(rong)量。不(bu)幸的(de)(de)是，用(yong)(yong)戶大(da)(da)(da)多比較心急(ji)，容(rong)量提高以(yi)后，還必須在一個合(he)理(li)的(de)(de)時間內充滿(man)電(dian)(dian)(dian)，這就(jiu)導致(zhi)要(yao)(yao)增大(da)(da)(da)充電(dian)(dian)(dian)電(dian)(dian)(dian)流。要(yao)(yao)滿(man)足(zu)第二種(zhong)需(xu)求(qiu)，就(jiu)要(yao)(yao)求(qiu)電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)解決方案提供極大(da)(da)(da)的(de)(de)靈活性。本文將更詳細地討論這些問題。

　　更大的功率

　　考慮一下新式手持式設(she)備(bei)(bei)(bei)，面(mian)向消費者的(de)設(she)備(bei)(bei)(bei)和工業設(she)備(bei)(bei)(bei)都可能(neng)包括蜂(feng)(feng)窩(wo)電(dian)(dian)(dian)話調制解調器、Wi-Fi模塊、藍牙(ya)模塊、大尺寸背光(guang)照明顯示屏(ping)…等等。很多手持式設(she)備(bei)(bei)(bei)的(de)電(dian)(dian)(dian)源架構都與蜂(feng)(feng)窩(wo)電(dian)(dian)(dian)話的(de)非(fei)常相似。一般情(qing)況下，用(yong)(yong)一個3.7V的(de)鋰(li)離(li)子(zi)(zi)電(dian)(dian)(dian)池(chi)作為主電(dian)(dian)(dian)源，因(yin)為鋰(li)離(li)子(zi)(zi)電(dian)(dian)(dian)池(chi)按(an)(an)重量(liang)和按(an)(an)體積(ji)的(de)能(neng)量(liang)密度(du)都很高(單位(wei)分別(bie)為Wh/kg和Wh/m3)。過去(qu)，很多大功(gong)率(lv)設(she)備(bei)(bei)(bei)都采用(yong)(yong)7.4V鋰(li)離(li)子(zi)(zi)電(dian)(dian)(dian)池(chi)，以降低電(dian)(dian)(dian)流(liu)要(yao)求，不過低價5V電(dian)(dian)(dian)源管理IC的(de)上市已經促使越來(lai)越多的(de)手持式設(she)備(bei)(bei)(bei)采用(yong)(yong)了電(dian)(dian)(dian)壓(ya)更低的(de)架構。平板電(dian)(dian)(dian)腦很好地(di)說明了這一點：一個典(dian)型的(de)平板電(dian)(dian)(dian)腦有極多的(de)功(gong)能(neng)以及(ji)非(fei)常大的(de)顯示屏(ping)(就便攜式設(she)備(bei)(bei)(bei)而言)。用(yong)(yong)3.7V電(dian)(dian)(dian)池(chi)供電(dian)(dian)(dian)時(shi)，其容量(liang)必須(xu)以數千毫安-小時(shi)計算。為了在幾(ji)個小時(shi)內給這樣一個電(dian)(dian)(dian)池(chi)充滿電(dian)(dian)(dian)，需要(yao)數千mA的(de)充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)。

　　然而，如果沒有大(da)電(dian)(dian)(dian)流(liu)交流(liu)適(shi)(shi)配(pei)(pei)(pei)器，盡管(guan)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)這(zhe)么高，也不能(neng)防止消費(fei)者用(yong)(yong)USB端口給(gei)大(da)功率(lv)設備充(chong)電(dian)(dian)(dian)的想(xiang)法(fa)。為了滿足這(zhe)種需求，當交流(liu)適(shi)(shi)配(pei)(pei)(pei)器可用(yong)(yong)時，電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)器必須能(neng)以大(da)電(dian)(dian)(dian)流(liu)(>2A)充(chong)電(dian)(dian)(dian)，而在沒有交流(liu)適(shi)(shi)配(pei)(pei)(pei)器可用(yong)(yong)時，電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)器必須仍能(neng)高效(xiao)地(di)利用(yong)(yong)USB端口提供(gong)2.5W至(zhi)4.5W功率(lv)。此外，器件必須保護敏(min)感的下游低壓組件免受可能(neng)出現過壓情況(kuang)所導致的損壞(huai)，同時必須無縫(feng)地(di)將大(da)電(dian)(dian)(dian)流(liu)從USB輸(shu)入(ru)、交流(liu)適(shi)(shi)配(pei)(pei)(pei)器或電(dian)(dian)(dian)池傳(chuan)送到負(fu)載(zai)，并最大(da)限度(du)地(di)降低功耗(hao)。另外，該IC還(huan)必須安全(quan)地(di)管(guan)理電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)算法(fa)，并監視關鍵(jian)的系(xi)統(tong)參數。

　　戰勝單節電池供電的便攜式(shi)產(chan)品(pin)在功率方面(mian)的挑戰

　　盡管看似不(bu)可能(neng)找到(dao)能(neng)滿足上述要求的(de)(de)單個IC，不(bu)過看一(yi)下LTC4155，這(zhe)(zhe)是一(yi)個大功率、I2C控制的(de)(de)高(gao)(gao)效率電(dian)(dian)(dian)源(yuan)通路(PowerPath?)管理(li)器、理(li)想二極管控制器和鋰(li)離子(zi)電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)器。該(gai)IC用來從(cong)各種(zhong)(zhong)5V電(dian)(dian)(dian)源(yuan)高(gao)(gao)效地傳送高(gao)(gao)達3A的(de)(de)電(dian)(dian)(dian)流，可產生超(chao)過3.5A的(de)(de)可用電(dian)(dian)(dian)流，以供(gong)電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)和系統使(shi)用(參(can)見(jian)圖(tu)1)。LTC4155的(de)(de)效率為(wei)88%至94%，因(yin)此即使(shi)電(dian)(dian)(dian)流值這(zhe)(zhe)么大，該(gai)IC仍然(ran)可以減輕熱(re)量(liang)預算限制(參(can)見(jian)圖(tu)2)。LTC4155的(de)(de)開(kai)關(guan)式(shi)電(dian)(dian)(dian)源(yuan)通路拓(tuo)撲無(wu)縫地管理(li)從(cong)兩種(zhong)(zhong)輸(shu)入電(dian)(dian)(dian)源(yuan)(例如(ru)一(yi)個交流適配(pei)器和一(yi)個USB端口)到(dao)設備中可再充(chong)電(dian)(dian)(dian)鋰(li)離子(zi)電(dian)(dian)(dian)池的(de)(de)配(pei)電(dian)(dian)(dian)，同時當輸(shu)入功率有限時，優先為(wei)系統負載(zai)供(gong)電(dian)(dian)(dian)。

圖1：LTC4155的典型應用電路(lu)

圖2：LTC4155的典型效率

　　與(yu)典型的(de)線性模(mo)式充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器相比，LTC4155中開關穩(wen)壓器的(de)作用就像(xiang)一個變壓器，允許VOUT上(shang)的(de)負載電(dian)(dian)(dian)(dian)(dian)流(liu)超過輸入電(dian)(dian)(dian)(dian)(dian)源吸取的(de)電(dian)(dian)(dian)(dian)(dian)流(liu)，并極(ji)大地提高電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)的(de)可(ke)用功(gong)率。前(qian)述(shu)例子說(shuo)明了(le)LTC4155怎樣(yang)才(cai)能(neng)以(yi)高達3.5A的(de)電(dian)(dian)(dian)(dian)(dian)流(liu)高效率地充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，以(yi)實現更快的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時間。與(yu)普通(tong)的(de)開關型電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器不同(tong)，LTC4155可(ke)即時接通(tong)工作，以(yi)確保即使電(dian)(dian)(dian)(dian)(dian)池(chi)沒電(dian)(dian)(dian)(dian)(dian)或已深度放電(dian)(dian)(dian)(dian)(dian)，當(dang)一插(cha)上(shang)電(dian)(dian)(dian)(dian)(dian)源插(cha)頭，系統電(dian)(dian)(dian)(dian)(dian)源也立即可(ke)用。

　　盡管(guan)是以(yi)很高的(de)(de)速率給電(dian)池充(chong)電(dian)，監(jian)(jian)視電(dian)池是否安全也是很重要的(de)(de)。當電(dian)池溫度(du)(du)(du)降至低于0°C或升至高于40°C[由一個(ge)(ge)外部負溫度(du)(du)(du)系數(NTC)熱敏電(dian)阻(zu)測量(liang)]時(shi)，LTC4155將自動停止充(chong)電(dian)。除了這種自主式功能，LTC4155還提供(gong)一個(ge)(ge)7位擴展(zhan)標度(du)(du)(du)模數轉換器(ADC)，以(yi)大約1°C的(de)(de)分辨率監(jian)(jian)視電(dian)池溫度(du)(du)(du)(參見圖3)。結合4個(ge)(ge)可用的(de)(de)浮置(zhi)電(dian)壓設定值(zhi)和15個(ge)(ge)電(dian)池充(chong)電(dian)電(dian)流(liu)設定值(zhi)，該ADC可基(ji)于電(dian)池溫度(du)(du)(du)來建立(li)定制的(de)(de)充(chong)電(dian)算法。

圖3：7位熱(re)敏電阻器ADC顯示LTC4155的預(yu)置(zhi)溫度跳變(bian)點(dian)

　　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、充電器狀態(tai)(tai)和故障狀態(tai)(tai)。由(you)于支持USBOTG，因此無需任何額外的組件，就可以反過(guo)來向USB端(duan)口提供(gong)5V電源。

　　LTC4155的雙路(lu)(lu)輸入(ru)(ru)、優(you)(you)先級(ji)多路(lu)(lu)復用器(qi)可根據用戶定義的優(you)(you)先級(ji)(默(mo)認的優(you)(you)先級(ji)為適配器(qi)輸入(ru)(ru))自主地選擇最合適的輸入(ru)(ru)(即墻上適配器(qi)或(huo)USB)。過壓保(bao)護(OVP)電路(lu)(lu)同時(shi)保(bao)護兩個輸入(ru)(ru)，以免這些(xie)輸入(ru)(ru)因無意間加上的高壓或(huo)反向電壓而損(sun)壞。LTC4155的理(li)想二極管(guan)控(kong)制器(qi)保(bao)證(zheng)即使輸入(ru)(ru)功率不足(zu)或(huo)未(wei)提供輸入(ru)(ru)功率時(shi)，也始終(zhong)可向VOUT提供足(zu)夠的功率。

　　就平板電(dian)(dian)腦、工業條碼掃描器(qi)(qi)等很多便(bian)攜式(shi)應(ying)用(yong)(yong)而言，能管理兩個輸(shu)入(ru)(例如USB和交流適配器(qi)(qi))就足夠(gou)了(le)。不過(guo)，便(bian)攜式(shi)設備的(de)設計師一直在尋求用(yong)(yong)任(ren)何可(ke)用(yong)(yong)電(dian)(dian)源(yuan)都(dou)能給電(dian)(dian)池充電(dian)(dian)的(de)方法

　　多種輸入源

　　用(yong)戶要(yao)用(yong)多種輸入(ru)源(yuan)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)有幾個原(yuan)因。有些(xie)(xie)應用(yong)也許需(xu)要(yao)擺脫電(dian)(dian)(dian)(dian)(dian)(dian)(dian)網的(de)束縛，而靠太陽(yang)能(neng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)板供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。另一(yi)些(xie)(xie)應用(yong)則可(ke)能(neng)要(yao)求能(neng)方便(bian)地用(yong)交流適配器、汽車(che)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)或(huo)(huo)高(gao)壓(ya)(ya)(ya)工業及(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。無論(lun)出(chu)于(yu)何(he)種原(yuan)因，這要(yao)求都給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)系統(tong)增(zeng)加了極大的(de)負擔。大多數電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器都利用(yong)降壓(ya)(ya)(ya)型(開關或(huo)(huo)線(xian)性)架(jia)構，用(yong)高(gao)于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)最高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)源(yuan)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。以(yi)前(qian)的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器產品(pin)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)一(yi)般限制(zhi)(zhi)為(wei)(wei)大約(yue)30V。這樣的(de)限制(zhi)(zhi)使(shi)(shi)(shi)設(she)計師(shi)無法(fa)將電(dian)(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)或(huo)(huo)者具42V開路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)太陽(yang)能(neng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)板作為(wei)(wei)可(ke)行的(de)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)。在有些(xie)(xie)情況下，希望使(shi)(shi)(shi)用(yong)的(de)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)涵蓋(gai)了高(gao)于(yu)和低于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)范圍。設(she)計一(yi)款應對此類難題的(de)解決方案通常需(xu)要(yao)混(hun)合(he)使(shi)(shi)(shi)用(yong)高(gao)精度(du)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流檢測放大器、ADC、一(yi)個用(yong)于(yu)控制(zhi)(zhi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)微處(chu)理(li)器、一(yi)個高(gao)性能(neng)DC/DC轉換器以(yi)及(ji)(ji)一(yi)個理(li)想二極管或(huo)(huo)多路(lu)復用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。

　　強大(da)的充電解決方案提供無(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(gao)性(xing)能(neng)便攜式儀器、電(dian)池(chi)后(hou)備系統(tong)、配有工業電(dian)池(chi)的(de)設備以及筆記本(ben)/小型筆記本(ben)電(dian)腦。

　　除(chu)了可以與很(hen)多(duo)不同的DC/DC拓撲(pu)結合，LTC4000的高壓能力(li)還允許該器(qi)件構成強(qiang)大和(he)幾乎可使用(yong)(yong)任何(he)輸(shu)入電(dian)(dian)源(yuan)(yuan)(參(can)見(jian)圖4和(he)圖5)的電(dian)(dian)池充(chong)電(dian)(dian)解決(jue)方案。為(wei)了確保來(lai)自這些輸(shu)入的功率(lv)傳送給合適的負載，LTC4000采(cai)用(yong)(yong)了一(yi)種智能電(dian)(dian)源(yuan)(yuan)通(tong)路拓撲(pu)，當輸(shu)入功率(lv)有(you)限(xian)時(shi)，該拓撲(pu)可優先(xian)為(wei)系統(tong)(tong)負載供電(dian)(dian)。LTC4000控制(zhi)外(wai)部PFET，以提供低(di)損耗反向電(dian)(dian)流保護(hu)、電(dian)(dian)池的低(di)損耗充(chong)電(dian)(dian)和(he)放電(dian)(dian)以及(ji)即(ji)時(shi)接通(tong)工作，這樣就可以確保即(ji)使在(zai)電(dian)(dian)池沒電(dian)(dian)或深度放電(dian)(dian)時(shi)，當一(yi)插(cha)上電(dian)(dian)源(yuan)(yuan)，系統(tong)(tong)電(dian)(dian)源(yuan)(yuan)就能立即(ji)可用(yong)(yong)。外(wai)部檢測電(dian)(dian)阻器(qi)提供輸(shu)入電(dian)(dian)流和(he)電(dian)(dian)池充(chong)電(dian)(dian)電(dian)(dian)流信息，從而使LTC4000能與涵蓋mW至kW功率(lv)范圍的轉換器(qi)一(yi)起(qi)使用(yong)(yong)。

圖4：LTC4000和LTC3789：6V至36V_IN、4節5A鋰(li)離子電(dian)池充電(dian)器

圖5：圖4電(dian)路中(zhong)系統負(fu)載為4A時效率隨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)提供精(jing)確的(de)電流檢測功能，從(cong)而在大電流應(ying)用(yong)情況下允許較(jiao)低的(de)檢測電壓。

　　結論

　　新式便攜(xie)式產(chan)品(pin)設(she)計(ji)師的工作(zuo)極富挑(tiao)戰性(xing)，尤(you)其是涉及到電(dian)(dian)源(yuan)時(shi)。客戶不斷要求(qiu)更多(duo)(duo)功能(neng)以導(dao)致需(xu)要更大(da)的功率，結果是電(dian)(dian)池越來越大(da)。同時(shi)，客戶希望可(ke)方(fang)(fang)便地(di)用幾乎任(ren)何可(ke)用的電(dian)(dian)源(yuan)給(gei)這些(xie)電(dian)(dian)池充電(dian)(dian)。盡管便攜(xie)式電(dian)(dian)源(yuan)領域的這些(xie)趨勢造成(cheng)(cheng)了(le)設(she)計(ji)挑(tiao)戰，但是LTC4155和(he)LTC4000讓設(she)計(ji)工作(zuo)變得簡(jian)單多(duo)(duo)了(le)。在低壓系統(tong)中(zhong)，LTC4155高(gao)效率地(di)提(ti)(ti)供高(gao)達3.5A的充電(dian)(dian)電(dian)(dian)流，而(er)且(qie)提(ti)(ti)供很多(duo)(duo)高(gao)性(xing)能(neng)功能(neng)。LTC4000可(ke)構成(cheng)(cheng)強大(da)的充電(dian)(dian)解決方(fang)(fang)案，而(er)且(qie)幾乎可(ke)使用任(ren)何輸(shu)入，從(cong)而(er)提(ti)(ti)供了(le)無與倫比的性(xing)能(neng)和(he)靈活性(xing)。