背景

　　便攜式電(dian)(dian)源(yuan)的(de)(de)應用(yong)范(fan)圍很廣，也很多樣化。產品包括消(xiao)耗uW級平均功(gong)率的(de)(de)無線傳感器(qi)節點(dian)以及可用(yong)小車推著的(de)(de)、電(dian)(dian)池(chi)組耗電(dian)(dian)數百瓦-時(shi)的(de)(de)醫(yi)療或數據采集系(xi)統。不(bu)過，盡管應用(yong)種類(lei)很多，仍然(ran)出現了幾個趨(qu)勢，設計師日益需(xu)要給產品提(ti)供更大(da)的(de)(de)功(gong)率，以支持(chi)不(bu)斷增多的(de)(de)功(gong)能，同時(shi)也在考慮怎樣用(yong)任何可用(yong)電(dian)(dian)源(yuan)給電(dian)(dian)池(chi)充電(dian)(dian)。要滿(man)足第(di)一種需(xu)求(qiu)，就要提(ti)高(gao)電(dian)(dian)池(chi)容量。不(bu)幸的(de)(de)是，用(yong)戶(hu)大(da)多比較心急，容量提(ti)高(gao)以后(hou)，還必(bi)須(xu)在一個合理的(de)(de)時(shi)間內充滿(man)電(dian)(dian)，這就導致要增大(da)充電(dian)(dian)電(dian)(dian)流。要滿(man)足第(di)二(er)種需(xu)求(qiu)，就要求(qiu)電(dian)(dian)池(chi)充電(dian)(dian)解決(jue)方案提(ti)供極大(da)的(de)(de)靈活性。本文將更詳(xiang)細(xi)地討論這些問題。

　　更大的功率

　　考慮(lv)一(yi)(yi)(yi)下新式(shi)手持式(shi)設(she)(she)(she)備(bei)，面向消費者的(de)(de)(de)設(she)(she)(she)備(bei)和(he)工業設(she)(she)(she)備(bei)都(dou)可(ke)能(neng)包括(kuo)蜂窩(wo)(wo)電(dian)(dian)話(hua)調制解調器、Wi-Fi模(mo)塊(kuai)、藍牙模(mo)塊(kuai)、大(da)尺寸背(bei)光照明(ming)顯示屏…等等。很(hen)(hen)(hen)多手持式(shi)設(she)(she)(she)備(bei)的(de)(de)(de)電(dian)(dian)源(yuan)架構都(dou)與(yu)蜂窩(wo)(wo)電(dian)(dian)話(hua)的(de)(de)(de)非(fei)常相(xiang)似。一(yi)(yi)(yi)般情況(kuang)下，用(yong)一(yi)(yi)(yi)個(ge)(ge)3.7V的(de)(de)(de)鋰離(li)子(zi)電(dian)(dian)池作為主電(dian)(dian)源(yuan)，因(yin)為鋰離(li)子(zi)電(dian)(dian)池按(an)重量(liang)和(he)按(an)體積的(de)(de)(de)能(neng)量(liang)密度(du)都(dou)很(hen)(hen)(hen)高(單(dan)位分別為Wh/kg和(he)Wh/m3)。過去，很(hen)(hen)(hen)多大(da)功率(lv)設(she)(she)(she)備(bei)都(dou)采用(yong)7.4V鋰離(li)子(zi)電(dian)(dian)池，以降(jiang)低電(dian)(dian)流要求，不過低價5V電(dian)(dian)源(yuan)管理IC的(de)(de)(de)上(shang)市已(yi)經促使越(yue)來越(yue)多的(de)(de)(de)手持式(shi)設(she)(she)(she)備(bei)采用(yong)了電(dian)(dian)壓(ya)更低的(de)(de)(de)架構。平板電(dian)(dian)腦很(hen)(hen)(hen)好地(di)說明(ming)了這一(yi)(yi)(yi)點(dian)：一(yi)(yi)(yi)個(ge)(ge)典型(xing)的(de)(de)(de)平板電(dian)(dian)腦有極(ji)多的(de)(de)(de)功能(neng)以及非(fei)常大(da)的(de)(de)(de)顯示屏(就便攜(xie)式(shi)設(she)(she)(she)備(bei)而言)。用(yong)3.7V電(dian)(dian)池供電(dian)(dian)時(shi)，其容量(liang)必(bi)須以數千毫安-小時(shi)計(ji)算。為了在(zai)幾個(ge)(ge)小時(shi)內(nei)給這樣(yang)一(yi)(yi)(yi)個(ge)(ge)電(dian)(dian)池充(chong)滿(man)電(dian)(dian)，需要數千mA的(de)(de)(de)充(chong)電(dian)(dian)電(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)(bi)須仍能高(gao)效地(di)利(li)用USB端口提供2.5W至4.5W功率(lv)。此外，器(qi)件必(bi)(bi)須保護(hu)敏感的(de)下游低壓(ya)(ya)組件免受可(ke)能出現(xian)過壓(ya)(ya)情(qing)況所(suo)導致的(de)損壞，同時必(bi)(bi)須無縫(feng)地(di)將大電(dian)流從USB輸入、交流適(shi)配器(qi)或電(dian)池(chi)傳送到負載(zai)，并(bing)最大限度地(di)降低功耗(hao)。另外，該IC還必(bi)(bi)須安全地(di)管理電(dian)池(chi)充電(dian)算(suan)法，并(bing)監視關(guan)鍵的(de)系統參(can)數。

　　戰勝單節電池供電的便攜式(shi)產品在功率方面(mian)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(yong)(yong)來從各種(zhong)5V電(dian)(dian)源高效地(di)(di)傳送(song)高達(da)3A的電(dian)(dian)流(liu)，可產生超過3.5A的可用(yong)(yong)電(dian)(dian)流(liu)，以供(gong)電(dian)(dian)池充(chong)(chong)電(dian)(dian)和(he)系(xi)(xi)統使(shi)用(yong)(yong)(參見圖1)。LTC4155的效率(lv)為88%至94%，因此即使(shi)電(dian)(dian)流(liu)值(zhi)這(zhe)么大，該IC仍然可以減輕熱(re)量預算(suan)限(xian)制(zhi)(參見圖2)。LTC4155的開關式(shi)電(dian)(dian)源通(tong)路拓撲無縫地(di)(di)管理從兩種(zhong)輸入電(dian)(dian)源(例(li)如一(yi)個(ge)交流(liu)適配器和(he)一(yi)個(ge)USB端口(kou))到設備中可再充(chong)(chong)電(dian)(dian)鋰離子(zi)電(dian)(dian)池的配電(dian)(dian)，同(tong)時(shi)當輸入功率(lv)有限(xian)時(shi)，優先為系(xi)(xi)統負載供(gong)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同，LTC4155可即(ji)時接通工作，以(yi)確保即(ji)使(shi)電(dian)池沒電(dian)或已深度放電(dian)，當一插上(shang)電(dian)源(yuan)插頭(tou)，系統電(dian)源(yuan)也立即(ji)可用。

　　盡(jin)管是以很高(gao)的(de)速(su)率(lv)給電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)，監視(shi)(shi)電(dian)(dian)(dian)(dian)池是否安全也是很重要的(de)。當電(dian)(dian)(dian)(dian)池溫(wen)(wen)度(du)(du)降至低于0°C或升(sheng)至高(gao)于40°C[由一個(ge)外部負(fu)溫(wen)(wen)度(du)(du)系(xi)數(NTC)熱敏電(dian)(dian)(dian)(dian)阻測量]時，LTC4155將自動停止充(chong)電(dian)(dian)(dian)(dian)。除了這種(zhong)自主式功能，LTC4155還提供(gong)一個(ge)7位擴展標(biao)度(du)(du)模(mo)數轉換器(ADC)，以大約(yue)1°C的(de)分辨率(lv)監視(shi)(shi)電(dian)(dian)(dian)(dian)池溫(wen)(wen)度(du)(du)(參(can)見圖3)。結(jie)合(he)4個(ge)可用的(de)浮(fu)置電(dian)(dian)(dian)(dian)壓設(she)定值和(he)15個(ge)電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)設(she)定值，該ADC可基(ji)于電(dian)(dian)(dian)(dian)池溫(wen)(wen)度(du)(du)來建立(li)定制(zhi)的(de)充(chong)電(dian)(dian)(dian)(dian)算法。

　通過(guo)一(yi)個簡(jian)單的(de)(de)(de)兩線I2C端口可獲得NTCADC的(de)(de)(de)結果，從(cong)而能(neng)調(diao)節充(chong)電(dian)(dian)電(dian)(dian)流(liu)和(he)(he)電(dian)(dian)壓的(de)(de)(de)設定值。該I2C端口通過(guo)控制(zhi)16個輸(shu)入電(dian)(dian)流(liu)的(de)(de)(de)設定值(包括USB2.0和(he)(he)3.0兼容設置)，還(huan)可提供USB兼容性。該通信(xin)總線允許LTC4155指示額外的(de)(de)(de)狀(zhuang)態(tai)(tai)信(xin)息，例如輸(shu)入電(dian)(dian)源狀(zhuang)態(tai)(tai)、充(chong)電(dian)(dian)器狀(zhuang)態(tai)(tai)和(he)(he)故障狀(zhuang)態(tai)(tai)。由于支持USBOTG，因此(ci)無(wu)需任(ren)何(he)額外的(de)(de)(de)組件，就可以反過(guo)來向USB端口提供5V電(dian)(dian)源。

　　LTC4155的(de)(de)雙路輸入(ru)(ru)、優(you)(you)先級多路復用器(qi)可根據用戶定義的(de)(de)優(you)(you)先級(默認(ren)的(de)(de)優(you)(you)先級為適(shi)配器(qi)輸入(ru)(ru))自主地選擇(ze)最合適(shi)的(de)(de)輸入(ru)(ru)(即墻上(shang)適(shi)配器(qi)或USB)。過壓保(bao)(bao)護(OVP)電路同時保(bao)(bao)護兩個輸入(ru)(ru)，以免(mian)這些輸入(ru)(ru)因無意間加(jia)上(shang)的(de)(de)高壓或反向電壓而(er)損(sun)壞。LTC4155的(de)(de)理想二極管控(kong)制器(qi)保(bao)(bao)證即使輸入(ru)(ru)功(gong)(gong)(gong)率(lv)不足(zu)或未提供輸入(ru)(ru)功(gong)(gong)(gong)率(lv)時，也(ye)始(shi)終可向VOUT提供足(zu)夠的(de)(de)功(gong)(gong)(gong)率(lv)。

　　就平板電(dian)腦、工業條碼掃描器(qi)等很多(duo)便攜(xie)式(shi)應用(yong)而言，能管理兩(liang)個輸入(例如USB和交流適(shi)配器(qi))就足(zu)夠了(le)。不(bu)過，便攜(xie)式(shi)設備的設計師一直在尋求用(yong)任何可用(yong)電(dian)源(yuan)都能給電(dian)池充電(dian)的方法(fa)

　　多種輸入源

　　用戶要(yao)(yao)用多種輸(shu)(shu)入(ru)(ru)源給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)有(you)幾個原(yuan)因(yin)。有(you)些(xie)應(ying)(ying)用也許需要(yao)(yao)擺脫(tuo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)網的(de)束縛，而(er)靠太陽能(neng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池板(ban)供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。另(ling)一(yi)些(xie)應(ying)(ying)用則(ze)可(ke)能(neng)要(yao)(yao)求能(neng)方(fang)便(bian)地用交流適配器(qi)、汽車電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池或(huo)高壓工業及電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。無論出于(yu)(yu)(yu)何(he)種原(yuan)因(yin)，這要(yao)(yao)求都(dou)(dou)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)系統增加(jia)了極大(da)的(de)負擔。大(da)多數(shu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)都(dou)(dou)利用降(jiang)壓型(開關或(huo)線性)架構(gou)，用高于(yu)(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池最(zui)高電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓源給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。以(yi)前的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)產品(pin)輸(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓一(yi)般限制為大(da)約30V。這樣的(de)限制使設計師無法將電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源或(huo)者具42V開路電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)太陽能(neng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池板(ban)作為可(ke)行的(de)輸(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源。在有(you)些(xie)情(qing)況下，希望使用的(de)輸(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓涵蓋(gai)了高于(yu)(yu)(yu)和低于(yu)(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)范圍。設計一(yi)款應(ying)(ying)對此類難題的(de)解決方(fang)案通(tong)常需要(yao)(yao)混(hun)合使用高精度的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流檢測放(fang)大(da)器(qi)、ADC、一(yi)個用于(yu)(yu)(yu)控制充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)微處理器(qi)、一(yi)個高性能(neng)DC/DC轉換器(qi)以(yi)及一(yi)個理想二極管或(huo)多路復(fu)用電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路。

　　強大(da)的充電解決(jue)方案提供無(wu)與倫比的靈活性(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(de)典型DC/DC轉換器(qi)拓撲包括但不(bu)限于：降(jiang)壓、升壓、降(jiang)壓-升壓、SEPIC和(he)反(fan)激式拓撲。該(gai)器(qi)件提供精確的(de)輸(shu)(shu)入和(he)充電(dian)電(dian)流調節，在3V至(zhi)60V的(de)寬(kuan)輸(shu)(shu)入和(he)輸(shu)(shu)出(chu)電(dian)壓范(fan)圍內工作，實現了與各種不(bu)同的(de)輸(shu)(shu)入電(dian)壓源、以(yi)及不(bu)同尺寸和(he)化(hua)學組成的(de)電(dian)池(chi)組的(de)兼容性。由于該(gai)器(qi)件的(de)通用(yong)型配置，因此其(qi)典型應用(yong)十分(fen)廣泛，包括高(gao)功率(lv)電(dian)池(chi)充電(dian)器(qi)系統(tong)(tong)、高(gao)性能便攜式儀(yi)器(qi)、電(dian)池(chi)后備(bei)系統(tong)(tong)、配有(you)工業電(dian)池(chi)的(de)設備(bei)以(yi)及筆(bi)(bi)記(ji)本/小(xiao)型筆(bi)(bi)記(ji)本電(dian)腦(nao)。

　　除(chu)了可(ke)(ke)以(yi)(yi)與很(hen)多不同的DC/DC拓撲(pu)(pu)結(jie)合，LTC4000的高壓(ya)能(neng)力還允許該(gai)(gai)器件構成強大和幾乎可(ke)(ke)使(shi)用(yong)任何輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)源(參見圖4和圖5)的電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)解決(jue)方案。為(wei)了確保來(lai)自這(zhe)些輸(shu)入(ru)(ru)的功率傳(chuan)送給合適的負(fu)載，LTC4000采(cai)用(yong)了一(yi)種(zhong)智(zhi)能(neng)電(dian)(dian)(dian)(dian)源通路拓撲(pu)(pu)，當輸(shu)入(ru)(ru)功率有限時(shi)，該(gai)(gai)拓撲(pu)(pu)可(ke)(ke)優先為(wei)系(xi)統(tong)負(fu)載供電(dian)(dian)(dian)(dian)。LTC4000控制(zhi)外(wai)(wai)部PFET，以(yi)(yi)提(ti)供低損耗反向電(dian)(dian)(dian)(dian)流保護、電(dian)(dian)(dian)(dian)池的低損耗充(chong)電(dian)(dian)(dian)(dian)和放(fang)電(dian)(dian)(dian)(dian)以(yi)(yi)及即(ji)時(shi)接通工作，這(zhe)樣(yang)就可(ke)(ke)以(yi)(yi)確保即(ji)使(shi)在電(dian)(dian)(dian)(dian)池沒電(dian)(dian)(dian)(dian)或深度放(fang)電(dian)(dian)(dian)(dian)時(shi)，當一(yi)插上電(dian)(dian)(dian)(dian)源，系(xi)統(tong)電(dian)(dian)(dian)(dian)源就能(neng)立即(ji)可(ke)(ke)用(yong)。外(wai)(wai)部檢測電(dian)(dian)(dian)(dian)阻器提(ti)供輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)流和電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流信息，從而使(shi)LTC4000能(neng)與涵蓋mW至kW功率范圍的轉換器一(yi)起使(shi)用(yong)。

　　LTC4000的(de)全功能電(dian)(dian)池充電(dian)(dian)控制(zhi)器可為(wei)各(ge)種化(hua)學組成的(de)電(dian)(dian)池充電(dian)(dian)，包括鋰離子/聚合物/磷(lin)酸(suan)、密封鉛酸(suan)(SLA)和鎳化(hua)學組成。該(gai)電(dian)(dian)池充電(dian)(dian)器還提(ti)供精(jing)確的(de)電(dian)(dian)流(liu)檢(jian)測功能，從而在大電(dian)(dian)流(liu)應用情況下允許較(jiao)低的(de)檢(jian)測電(dian)(dian)壓。

　　結論

　　新式便(bian)攜式產(chan)品設計師的(de)(de)(de)工(gong)作極富挑戰性(xing)，尤其是涉及(ji)到電(dian)(dian)源(yuan)(yuan)時。客戶不斷(duan)要求更(geng)多(duo)(duo)功(gong)能(neng)以導(dao)致需要更(geng)大(da)的(de)(de)(de)功(gong)率，結(jie)果是電(dian)(dian)池越來越大(da)。同時，客戶希望(wang)可(ke)方便(bian)地用(yong)(yong)(yong)幾(ji)乎任(ren)(ren)何可(ke)用(yong)(yong)(yong)的(de)(de)(de)電(dian)(dian)源(yuan)(yuan)給這些電(dian)(dian)池充(chong)電(dian)(dian)。盡(jin)管便(bian)攜式電(dian)(dian)源(yuan)(yuan)領(ling)域的(de)(de)(de)這些趨勢(shi)造成了設計挑戰，但是LTC4155和LTC4000讓設計工(gong)作變(bian)得(de)簡單多(duo)(duo)了。在低(di)壓(ya)系統(tong)中，LTC4155高(gao)(gao)效率地提供高(gao)(gao)達3.5A的(de)(de)(de)充(chong)電(dian)(dian)電(dian)(dian)流(liu)，而(er)且提供很多(duo)(duo)高(gao)(gao)性(xing)能(neng)功(gong)能(neng)。LTC4000可(ke)構成強大(da)的(de)(de)(de)充(chong)電(dian)(dian)解決方案，而(er)且幾(ji)乎可(ke)使(shi)用(yong)(yong)(yong)任(ren)(ren)何輸入，從而(er)提供了無與倫比的(de)(de)(de)性(xing)能(neng)和靈(ling)活性(xing)。