背景

　　便攜式(shi)電(dian)源的(de)(de)(de)應(ying)用范圍很(hen)廣，也很(hen)多樣(yang)化。產品包括(kuo)消耗uW級(ji)平均功(gong)(gong)率(lv)的(de)(de)(de)無線傳感器(qi)節點以及可用小車(che)推著的(de)(de)(de)、電(dian)池(chi)組耗電(dian)數(shu)(shu)百(bai)瓦(wa)-時(shi)的(de)(de)(de)醫療或數(shu)(shu)據采集系(xi)統。不(bu)過(guo)，盡(jin)管應(ying)用種(zhong)類很(hen)多，仍(reng)然出現了幾個(ge)趨勢，設計師(shi)日益需(xu)要給(gei)產品提供更大(da)的(de)(de)(de)功(gong)(gong)率(lv)，以支持不(bu)斷增(zeng)多的(de)(de)(de)功(gong)(gong)能，同時(shi)也在(zai)考慮(lv)怎樣(yang)用任何可用電(dian)源給(gei)電(dian)池(chi)充電(dian)。要滿足第(di)一(yi)種(zhong)需(xu)求(qiu)，就要提高電(dian)池(chi)容量。不(bu)幸(xing)的(de)(de)(de)是，用戶大(da)多比(bi)較心急，容量提高以后，還必(bi)須在(zai)一(yi)個(ge)合理的(de)(de)(de)時(shi)間(jian)內充滿電(dian)，這就導致(zhi)要增(zeng)大(da)充電(dian)電(dian)流。要滿足第(di)二種(zhong)需(xu)求(qiu)，就要求(qiu)電(dian)池(chi)充電(dian)解決方(fang)案提供極大(da)的(de)(de)(de)靈活性。本文將更詳細地(di)討論這些問題。

　　更大的功率

　　考慮一(yi)下新式手(shou)持式設(she)(she)(she)備(bei)(bei)(bei)(bei)(bei)，面向消費者的(de)(de)(de)(de)設(she)(she)(she)備(bei)(bei)(bei)(bei)(bei)和(he)工業設(she)(she)(she)備(bei)(bei)(bei)(bei)(bei)都可(ke)能包(bao)括蜂窩(wo)電(dian)(dian)(dian)(dian)話(hua)調(diao)制解(jie)調(diao)器(qi)、Wi-Fi模(mo)塊、藍(lan)牙模(mo)塊、大尺寸(cun)背光照(zhao)明(ming)顯示(shi)屏…等等。很多(duo)手(shou)持式設(she)(she)(she)備(bei)(bei)(bei)(bei)(bei)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)源架構都與(yu)蜂窩(wo)電(dian)(dian)(dian)(dian)話(hua)的(de)(de)(de)(de)非(fei)(fei)常相似。一(yi)般(ban)情況下，用(yong)一(yi)個3.7V的(de)(de)(de)(de)鋰(li)離子電(dian)(dian)(dian)(dian)池(chi)作為(wei)主電(dian)(dian)(dian)(dian)源，因(yin)為(wei)鋰(li)離子電(dian)(dian)(dian)(dian)池(chi)按重量(liang)和(he)按體積的(de)(de)(de)(de)能量(liang)密度都很高(單位分別為(wei)Wh/kg和(he)Wh/m3)。過去(qu)，很多(duo)大功(gong)率設(she)(she)(she)備(bei)(bei)(bei)(bei)(bei)都采(cai)用(yong)7.4V鋰(li)離子電(dian)(dian)(dian)(dian)池(chi)，以降(jiang)低(di)電(dian)(dian)(dian)(dian)流(liu)要求(qiu)，不過低(di)價5V電(dian)(dian)(dian)(dian)源管理IC的(de)(de)(de)(de)上市已經促使(shi)越(yue)來越(yue)多(duo)的(de)(de)(de)(de)手(shou)持式設(she)(she)(she)備(bei)(bei)(bei)(bei)(bei)采(cai)用(yong)了電(dian)(dian)(dian)(dian)壓更低(di)的(de)(de)(de)(de)架構。平板電(dian)(dian)(dian)(dian)腦很好地說明(ming)了這(zhe)一(yi)點(dian)：一(yi)個典型的(de)(de)(de)(de)平板電(dian)(dian)(dian)(dian)腦有極多(duo)的(de)(de)(de)(de)功(gong)能以及(ji)非(fei)(fei)常大的(de)(de)(de)(de)顯示(shi)屏(就便攜式設(she)(she)(she)備(bei)(bei)(bei)(bei)(bei)而(er)言(yan))。用(yong)3.7V電(dian)(dian)(dian)(dian)池(chi)供電(dian)(dian)(dian)(dian)時，其(qi)容量(liang)必須(xu)以數千毫(hao)安-小時計(ji)算。為(wei)了在(zai)幾個小時內給這(zhe)樣一(yi)個電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)滿電(dian)(dian)(dian)(dian)，需(xu)要數千mA的(de)(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(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)須仍能高效地(di)(di)利用USB端口提供(gong)2.5W至(zhi)4.5W功率。此外，器(qi)件必(bi)須保(bao)護敏(min)感的下游低壓組件免(mian)受可能出現過壓情況所導致的損壞(huai)，同時必(bi)須無縫地(di)(di)將大電(dian)流(liu)從USB輸入、交流(liu)適配器(qi)或電(dian)池(chi)傳送到負載，并最大限度地(di)(di)降(jiang)低功耗。另外，該IC還必(bi)須安全地(di)(di)管理電(dian)池(chi)充(chong)電(dian)算法，并監視關鍵的系統參數。

　　戰勝單節電池供電的(de)便攜(xie)式(shi)產品(pin)在功率(lv)方面的(de)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電源(yuan)高效地傳送(song)高達3A的(de)(de)電流，可(ke)產生(sheng)超過3.5A的(de)(de)可(ke)用電流，以(yi)供電池充電和系統使用(參見(jian)圖1)。LTC4155的(de)(de)效率為(wei)88%至94%，因此即(ji)使電流值(zhi)這么大，該IC仍然(ran)可(ke)以(yi)減(jian)輕熱(re)量預算限(xian)制(參見(jian)圖2)。LTC4155的(de)(de)開關(guan)式電源(yuan)通路(lu)拓撲(pu)無縫地管理從兩種輸(shu)入電源(yuan)(例如一個(ge)交流適配器和一個(ge)USB端口)到設備中可(ke)再(zai)充電鋰(li)離子電池的(de)(de)配電，同時(shi)當輸(shu)入功(gong)率有限(xian)時(shi)，優(you)先為(wei)系統負載供電。

　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)(ji)時(shi)接通工作，以(yi)確保(bao)即(ji)(ji)使電池(chi)沒電或已(yi)深(shen)度(du)放電，當一(yi)插上電源(yuan)插頭(tou)，系(xi)統電源(yuan)也立即(ji)(ji)可用。

　　盡管是(shi)以很高(gao)的(de)速率(lv)給電(dian)(dian)(dian)池充電(dian)(dian)(dian)，監視電(dian)(dian)(dian)池是(shi)否(fou)安全也是(shi)很重要的(de)。當電(dian)(dian)(dian)池溫度降至低(di)于0°C或升(sheng)至高(gao)于40°C[由一個外部負溫度系數(NTC)熱敏電(dian)(dian)(dian)阻測量]時，LTC4155將自動停止充電(dian)(dian)(dian)。除了這種(zhong)自主式功能，LTC4155還提(ti)供一個7位擴展標度模數轉換器(ADC)，以大(da)約1°C的(de)分辨率(lv)監視電(dian)(dian)(dian)池溫度(參見圖3)。結(jie)合4個可用的(de)浮置電(dian)(dian)(dian)壓設定(ding)(ding)值(zhi)和15個電(dian)(dian)(dian)池充電(dian)(dian)(dian)電(dian)(dian)(dian)流設定(ding)(ding)值(zhi)，該ADC可基于電(dian)(dian)(dian)池溫度來建立定(ding)(ding)制的(de)充電(dian)(dian)(dian)算法。

　通過一個(ge)簡單的(de)兩線(xian)I2C端口可(ke)(ke)獲得NTCADC的(de)結果，從而能(neng)調節充(chong)電(dian)(dian)電(dian)(dian)流和電(dian)(dian)壓的(de)設定(ding)值。該I2C端口通過控制16個(ge)輸入電(dian)(dian)流的(de)設定(ding)值(包括USB2.0和3.0兼容設置)，還(huan)可(ke)(ke)提供USB兼容性。該通信總線(xian)允許LTC4155指示(shi)額外(wai)的(de)狀(zhuang)態信息(xi)，例如(ru)輸入電(dian)(dian)源(yuan)狀(zhuang)態、充(chong)電(dian)(dian)器(qi)狀(zhuang)態和故障狀(zhuang)態。由于支(zhi)持(chi)USBOTG，因此無需任何(he)額外(wai)的(de)組件(jian)，就可(ke)(ke)以反過來(lai)向(xiang)USB端口提供5V電(dian)(dian)源(yuan)。

　　LTC4155的(de)雙路(lu)輸(shu)(shu)入(ru)、優(you)先級多(duo)路(lu)復用器可根據(ju)用戶定義的(de)優(you)先級(默認(ren)的(de)優(you)先級為適(shi)配器輸(shu)(shu)入(ru))自主地選擇最合適(shi)的(de)輸(shu)(shu)入(ru)(即墻(qiang)上適(shi)配器或USB)。過壓(ya)(ya)保(bao)護(OVP)電路(lu)同時保(bao)護兩個輸(shu)(shu)入(ru)，以(yi)免(mian)這些輸(shu)(shu)入(ru)因無意間加上的(de)高(gao)壓(ya)(ya)或反(fan)向(xiang)電壓(ya)(ya)而(er)損壞(huai)。LTC4155的(de)理想(xiang)二極管控制器保(bao)證即使(shi)輸(shu)(shu)入(ru)功(gong)率(lv)(lv)不足或未(wei)提供(gong)輸(shu)(shu)入(ru)功(gong)率(lv)(lv)時，也始終可向(xiang)VOUT提供(gong)足夠的(de)功(gong)率(lv)(lv)。

　　就平(ping)板電腦(nao)、工業(ye)條碼掃描器等很多(duo)便攜式應用而言，能(neng)管(guan)理(li)兩個輸(shu)入(例如(ru)USB和交流適(shi)配器)就足(zu)夠了。不過(guo)，便攜式設備的設計師一直在尋求(qiu)用任何可用電源都能(neng)給電池充電的方法

　　多種輸入源

　　用(yong)(yong)(yong)(yong)(yong)戶要(yao)用(yong)(yong)(yong)(yong)(yong)多種輸(shu)入(ru)(ru)(ru)源給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)有幾個原因(yin)。有些應(ying)用(yong)(yong)(yong)(yong)(yong)也許需要(yao)擺脫電(dian)(dian)(dian)(dian)(dian)(dian)(dian)網的束縛，而靠太陽能電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)板供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。另一(yi)(yi)些應(ying)用(yong)(yong)(yong)(yong)(yong)則可能要(yao)求(qiu)能方便地用(yong)(yong)(yong)(yong)(yong)交流適配器(qi)(qi)、汽車電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)或(huo)高(gao)(gao)壓(ya)(ya)工業及電(dian)(dian)(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。無論出于(yu)何種原因(yin)，這(zhe)要(yao)求(qiu)都(dou)給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)系統增(zeng)加了極(ji)大的負擔。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(qi)(qi)都(dou)利用(yong)(yong)(yong)(yong)(yong)降(jiang)壓(ya)(ya)型(開關或(huo)線性(xing)(xing))架構，用(yong)(yong)(yong)(yong)(yong)高(gao)(gao)于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)最高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)源給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。以前的充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)產品輸(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)一(yi)(yi)般限制(zhi)為大約30V。這(zhe)樣(yang)的限制(zhi)使(shi)(shi)設計(ji)師無法(fa)將電(dian)(dian)(dian)(dian)(dian)(dian)(dian)信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源或(huo)者具(ju)42V開路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)的太陽能電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)板作為可行的輸(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源。在(zai)有些情況下，希望使(shi)(shi)用(yong)(yong)(yong)(yong)(yong)的輸(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)涵蓋(gai)了高(gao)(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)的范圍(wei)。設計(ji)一(yi)(yi)款(kuan)應(ying)對此類難題的解(jie)決(jue)方案通常需要(yao)混合使(shi)(shi)用(yong)(yong)(yong)(yong)(yong)高(gao)(gao)精(jing)度的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流檢測放大器(qi)(qi)、ADC、一(yi)(yi)個用(yong)(yong)(yong)(yong)(yong)于(yu)控制(zhi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的微處理器(qi)(qi)、一(yi)(yi)個高(gao)(gao)性(xing)(xing)能DC/DC轉換器(qi)(qi)以及一(yi)(yi)個理想二極(ji)管或(huo)多路(lu)復用(yong)(yong)(yong)(yong)(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。

　　強大的(de)充電解決方案提供無(wu)與倫比的(de)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(dian)型(xing)(xing)DC/DC轉(zhuan)換器拓撲包括(kuo)但不(bu)限于(yu)：降壓(ya)(ya)、升(sheng)壓(ya)(ya)、降壓(ya)(ya)-升(sheng)壓(ya)(ya)、SEPIC和(he)反激式拓撲。該(gai)器件提供精確(que)的輸入和(he)充電(dian)(dian)(dian)電(dian)(dian)(dian)流調(diao)節，在(zai)3V至60V的寬輸入和(he)輸出電(dian)(dian)(dian)壓(ya)(ya)范圍內工作，實現了(le)與各(ge)種(zhong)不(bu)同的輸入電(dian)(dian)(dian)壓(ya)(ya)源(yuan)、以及不(bu)同尺寸和(he)化(hua)學組(zu)成(cheng)的電(dian)(dian)(dian)池(chi)組(zu)的兼容性(xing)。由于(yu)該(gai)器件的通用型(xing)(xing)配置(zhi)，因此其典(dian)型(xing)(xing)應用十分廣泛，包括(kuo)高功(gong)率電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)器系統(tong)、高性(xing)能便攜式儀器、電(dian)(dian)(dian)池(chi)后備系統(tong)、配有工業電(dian)(dian)(dian)池(chi)的設(she)備以及筆記(ji)本/小型(xing)(xing)筆記(ji)本電(dian)(dian)(dian)腦(nao)。

　　除了可(ke)(ke)以(yi)與很多(duo)不同的(de)(de)DC/DC拓(tuo)撲結合，LTC4000的(de)(de)高壓能(neng)力(li)還允許該(gai)器(qi)件構(gou)成(cheng)強大和幾乎可(ke)(ke)使用(yong)任何(he)輸入電(dian)(dian)(dian)(dian)源(yuan)(參(can)見圖(tu)4和圖(tu)5)的(de)(de)電(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)解決方(fang)案。為了確(que)保(bao)來自(zi)這些(xie)輸入的(de)(de)功率傳送給合適的(de)(de)負載(zai)(zai)，LTC4000采用(yong)了一(yi)種智能(neng)電(dian)(dian)(dian)(dian)源(yuan)通(tong)路拓(tuo)撲，當輸入功率有限時(shi)，該(gai)拓(tuo)撲可(ke)(ke)優先為系(xi)統負載(zai)(zai)供電(dian)(dian)(dian)(dian)。LTC4000控制外部PFET，以(yi)提供低損(sun)耗(hao)反向電(dian)(dian)(dian)(dian)流(liu)(liu)保(bao)護、電(dian)(dian)(dian)(dian)池(chi)的(de)(de)低損(sun)耗(hao)充電(dian)(dian)(dian)(dian)和放電(dian)(dian)(dian)(dian)以(yi)及即(ji)時(shi)接通(tong)工作(zuo)，這樣就(jiu)可(ke)(ke)以(yi)確(que)保(bao)即(ji)使在電(dian)(dian)(dian)(dian)池(chi)沒電(dian)(dian)(dian)(dian)或深度放電(dian)(dian)(dian)(dian)時(shi)，當一(yi)插上電(dian)(dian)(dian)(dian)源(yuan)，系(xi)統電(dian)(dian)(dian)(dian)源(yuan)就(jiu)能(neng)立(li)即(ji)可(ke)(ke)用(yong)。外部檢(jian)測電(dian)(dian)(dian)(dian)阻器(qi)提供輸入電(dian)(dian)(dian)(dian)流(liu)(liu)和電(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)信息，從而使LTC4000能(neng)與涵蓋(gai)mW至kW功率范圍的(de)(de)轉(zhuan)換(huan)器(qi)一(yi)起使用(yong)。

　　LTC4000的(de)全功能電(dian)(dian)池(chi)充電(dian)(dian)控制器可為各種(zhong)化學組成(cheng)(cheng)的(de)電(dian)(dian)池(chi)充電(dian)(dian)，包括鋰(li)離子/聚合物/磷(lin)酸、密封鉛酸(SLA)和(he)鎳化學組成(cheng)(cheng)。該電(dian)(dian)池(chi)充電(dian)(dian)器還提供精確的(de)電(dian)(dian)流檢(jian)測功能，從而在大電(dian)(dian)流應用情(qing)況下允許較低的(de)檢(jian)測電(dian)(dian)壓。

　　結論

　　新式(shi)(shi)便(bian)攜式(shi)(shi)產品設(she)(she)計(ji)師的(de)(de)(de)(de)工作極富挑戰性(xing)(xing)，尤(you)其是涉及到電(dian)(dian)源(yuan)時。客戶不斷要求更多(duo)功(gong)(gong)能以導(dao)致(zhi)需要更大(da)的(de)(de)(de)(de)功(gong)(gong)率，結果(guo)是電(dian)(dian)池(chi)(chi)越來越大(da)。同時，客戶希望(wang)可(ke)方便(bian)地用(yong)幾(ji)乎任何(he)可(ke)用(yong)的(de)(de)(de)(de)電(dian)(dian)源(yuan)給這(zhe)些電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)。盡管便(bian)攜式(shi)(shi)電(dian)(dian)源(yuan)領(ling)域的(de)(de)(de)(de)這(zhe)些趨勢造(zao)成(cheng)(cheng)了(le)設(she)(she)計(ji)挑戰，但是LTC4155和LTC4000讓(rang)設(she)(she)計(ji)工作變得簡單多(duo)了(le)。在低壓系統中(zhong)，LTC4155高(gao)效(xiao)率地提供(gong)高(gao)達3.5A的(de)(de)(de)(de)充(chong)電(dian)(dian)電(dian)(dian)流，而且提供(gong)很多(duo)高(gao)性(xing)(xing)能功(gong)(gong)能。LTC4000可(ke)構成(cheng)(cheng)強大(da)的(de)(de)(de)(de)充(chong)電(dian)(dian)解(jie)決方案，而且幾(ji)乎可(ke)使用(yong)任何(he)輸入，從而提供(gong)了(le)無與倫比的(de)(de)(de)(de)性(xing)(xing)能和靈活性(xing)(xing)。