背景

　　便攜式電(dian)源(yuan)的(de)應(ying)用(yong)范圍很(hen)(hen)廣，也(ye)很(hen)(hen)多(duo)樣化。產品包括消耗uW級平均功率(lv)的(de)無線傳(chuan)感(gan)器節(jie)點以(yi)及可用(yong)小車推著的(de)、電(dian)池(chi)組耗電(dian)數(shu)百瓦-時的(de)醫療或(huo)數(shu)據(ju)采集系(xi)統。不(bu)過，盡管應(ying)用(yong)種類很(hen)(hen)多(duo)，仍然出現了幾個(ge)趨勢，設計師(shi)日(ri)益需要(yao)(yao)(yao)給(gei)產品提供更大(da)的(de)功率(lv)，以(yi)支持不(bu)斷增多(duo)的(de)功能，同時也(ye)在(zai)考慮(lv)怎樣用(yong)任何可用(yong)電(dian)源(yuan)給(gei)電(dian)池(chi)充電(dian)。要(yao)(yao)(yao)滿足第一種需求(qiu)，就要(yao)(yao)(yao)提高(gao)電(dian)池(chi)容(rong)量。不(bu)幸的(de)是，用(yong)戶(hu)大(da)多(duo)比(bi)較心急(ji)，容(rong)量提高(gao)以(yi)后(hou)，還必須在(zai)一個(ge)合(he)理的(de)時間內充滿電(dian)，這就導致(zhi)要(yao)(yao)(yao)增大(da)充電(dian)電(dian)流(liu)。要(yao)(yao)(yao)滿足第二種需求(qiu)，就要(yao)(yao)(yao)求(qiu)電(dian)池(chi)充電(dian)解決方案提供極(ji)大(da)的(de)靈活性(xing)。本文將更詳細地討(tao)論這些問題。

　　更大的功率

　　考慮一(yi)下新式(shi)(shi)(shi)手持式(shi)(shi)(shi)設(she)(she)備(bei)(bei)(bei)(bei)(bei)，面向(xiang)消費者的(de)(de)(de)(de)設(she)(she)備(bei)(bei)(bei)(bei)(bei)和工業設(she)(she)備(bei)(bei)(bei)(bei)(bei)都(dou)可(ke)能(neng)包括(kuo)蜂(feng)窩電(dian)(dian)(dian)(dian)(dian)話調制解調器、Wi-Fi模塊(kuai)、藍牙模塊(kuai)、大(da)尺(chi)寸背(bei)光照明(ming)顯(xian)示(shi)屏…等等。很(hen)多(duo)(duo)手持式(shi)(shi)(shi)設(she)(she)備(bei)(bei)(bei)(bei)(bei)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)源架構都(dou)與蜂(feng)窩電(dian)(dian)(dian)(dian)(dian)話的(de)(de)(de)(de)非(fei)常(chang)相似(si)。一(yi)般情況下，用一(yi)個(ge)3.7V的(de)(de)(de)(de)鋰離子電(dian)(dian)(dian)(dian)(dian)池作為(wei)主(zhu)電(dian)(dian)(dian)(dian)(dian)源，因為(wei)鋰離子電(dian)(dian)(dian)(dian)(dian)池按重量和按體(ti)積的(de)(de)(de)(de)能(neng)量密度都(dou)很(hen)高(gao)(單位分別為(wei)Wh/kg和Wh/m3)。過(guo)去，很(hen)多(duo)(duo)大(da)功率設(she)(she)備(bei)(bei)(bei)(bei)(bei)都(dou)采用7.4V鋰離子電(dian)(dian)(dian)(dian)(dian)池，以降低電(dian)(dian)(dian)(dian)(dian)流(liu)要求，不過(guo)低價5V電(dian)(dian)(dian)(dian)(dian)源管理IC的(de)(de)(de)(de)上市已經促使越(yue)(yue)來越(yue)(yue)多(duo)(duo)的(de)(de)(de)(de)手持式(shi)(shi)(shi)設(she)(she)備(bei)(bei)(bei)(bei)(bei)采用了電(dian)(dian)(dian)(dian)(dian)壓更低的(de)(de)(de)(de)架構。平(ping)板(ban)電(dian)(dian)(dian)(dian)(dian)腦很(hen)好地說明(ming)了這一(yi)點(dian)：一(yi)個(ge)典(dian)型的(de)(de)(de)(de)平(ping)板(ban)電(dian)(dian)(dian)(dian)(dian)腦有(you)極多(duo)(duo)的(de)(de)(de)(de)功能(neng)以及非(fei)常(chang)大(da)的(de)(de)(de)(de)顯(xian)示(shi)屏(就便攜式(shi)(shi)(shi)設(she)(she)備(bei)(bei)(bei)(bei)(bei)而言)。用3.7V電(dian)(dian)(dian)(dian)(dian)池供電(dian)(dian)(dian)(dian)(dian)時，其容量必須以數千毫安-小時計算。為(wei)了在(zai)幾個(ge)小時內給這樣(yang)一(yi)個(ge)電(dian)(dian)(dian)(dian)(dian)池充滿電(dian)(dian)(dian)(dian)(dian)，需要數千mA的(de)(de)(de)(de)充電(dian)(dian)(dian)(dian)(dian)電(dian)(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，電池充電器必須仍能高(gao)效地(di)利用USB端口(kou)提供2.5W至4.5W功(gong)率。此外，器件必須保護敏感的(de)(de)下游低壓組件免受可(ke)能出現過壓情況所導致的(de)(de)損(sun)壞(huai)，同時必須無縫地(di)將大(da)電(dian)流從USB輸入、交流適(shi)配(pei)器或電(dian)池(chi)(chi)傳送到(dao)負載，并最大(da)限度地(di)降低功(gong)耗。另(ling)外，該IC還必須安全(quan)地(di)管理電(dian)池(chi)(chi)充電(dian)算(suan)法，并監視(shi)關鍵的(de)(de)系(xi)統(tong)參(can)數。

　　戰(zhan)勝單節電(dian)池供電(dian)的便(bian)攜式(shi)產品在功率方面的挑(tiao)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(lai)從各(ge)種(zhong)5V電(dian)(dian)(dian)源(yuan)高效地傳(chuan)送高達3A的(de)電(dian)(dian)(dian)流(liu)，可產生超過3.5A的(de)可用電(dian)(dian)(dian)流(liu)，以供電(dian)(dian)(dian)池充電(dian)(dian)(dian)和系統(tong)使用(參見(jian)圖1)。LTC4155的(de)效率為(wei)88%至(zhi)94%，因此即(ji)使電(dian)(dian)(dian)流(liu)值這么大，該IC仍然可以減輕熱量預算限(xian)制(zhi)(參見(jian)圖2)。LTC4155的(de)開關式電(dian)(dian)(dian)源(yuan)通路(lu)拓撲無縫(feng)地管理從兩種(zhong)輸(shu)入(ru)電(dian)(dian)(dian)源(yuan)(例如一個交流(liu)適配(pei)器和一個USB端口)到(dao)設備中可再充電(dian)(dian)(dian)鋰離子電(dian)(dian)(dian)池的(de)配(pei)電(dian)(dian)(dian)，同時(shi)當輸(shu)入(ru)功率有限(xian)時(shi)，優(you)先為(wei)系統(tong)負載供電(dian)(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(zuo)，以(yi)確保即(ji)使電池沒電或已深(shen)度放電，當一插(cha)上電源(yuan)插(cha)頭(tou)，系(xi)統電源(yuan)也立即(ji)可用(yong)。

　　盡管是(shi)以(yi)很高的(de)速(su)率(lv)給(gei)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)，監視電(dian)(dian)(dian)池(chi)是(shi)否安全也(ye)是(shi)很重要的(de)。當電(dian)(dian)(dian)池(chi)溫度降至(zhi)低于0°C或(huo)升至(zhi)高于40°C[由一個(ge)外部負(fu)溫度系數(NTC)熱敏電(dian)(dian)(dian)阻測量]時，LTC4155將自(zi)動停(ting)止(zhi)充(chong)電(dian)(dian)(dian)。除了這種自(zi)主式(shi)功能，LTC4155還提供(gong)一個(ge)7位擴展標度模數轉(zhuan)換器(qi)(ADC)，以(yi)大(da)約(yue)1°C的(de)分辨率(lv)監視電(dian)(dian)(dian)池(chi)溫度(參見圖3)。結合(he)4個(ge)可用的(de)浮置(zhi)電(dian)(dian)(dian)壓設定(ding)值和15個(ge)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流設定(ding)值，該(gai)ADC可基于電(dian)(dian)(dian)池(chi)溫度來建立定(ding)制的(de)充(chong)電(dian)(dian)(dian)算法(fa)。

　通(tong)(tong)過一個簡單的兩線(xian)I2C端口可獲得NTCADC的結果，從而能(neng)調節充電電流和(he)電壓(ya)的設定(ding)值。該I2C端口通(tong)(tong)過控制16個輸入電流的設定(ding)值(包括(kuo)USB2.0和(he)3.0兼(jian)容設置)，還可提供USB兼(jian)容性。該通(tong)(tong)信總線(xian)允許LTC4155指示(shi)額(e)(e)外(wai)的狀(zhuang)態(tai)信息，例如輸入電源狀(zhuang)態(tai)、充電器狀(zhuang)態(tai)和(he)故障狀(zhuang)態(tai)。由于支持USBOTG，因此(ci)無需任何額(e)(e)外(wai)的組件，就可以反過來向(xiang)USB端口提供5V電源。

　　LTC4155的(de)(de)(de)雙路輸(shu)入(ru)、優(you)先級多(duo)路復(fu)用器可根據用戶定義的(de)(de)(de)優(you)先級(默(mo)認的(de)(de)(de)優(you)先級為適(shi)配器輸(shu)入(ru))自主(zhu)地選擇最合適(shi)的(de)(de)(de)輸(shu)入(ru)(即墻(qiang)上(shang)適(shi)配器或(huo)USB)。過壓(ya)保(bao)護(hu)(OVP)電路同(tong)時保(bao)護(hu)兩個輸(shu)入(ru)，以免這些輸(shu)入(ru)因(yin)無意間加(jia)上(shang)的(de)(de)(de)高壓(ya)或(huo)反向電壓(ya)而損(sun)壞。LTC4155的(de)(de)(de)理想二極管控(kong)制器保(bao)證即使輸(shu)入(ru)功(gong)率不足或(huo)未提(ti)供(gong)輸(shu)入(ru)功(gong)率時，也始終可向VOUT提(ti)供(gong)足夠的(de)(de)(de)功(gong)率。

　　就平板電(dian)(dian)腦、工業條碼掃(sao)描器(qi)等很(hen)多便攜(xie)式應用而言(yan)，能管理(li)兩(liang)個輸入(ru)(例如USB和交流適配器(qi))就足(zu)夠了。不(bu)過，便攜(xie)式設(she)備的設(she)計師一直在尋求用任何(he)可用電(dian)(dian)源都能給電(dian)(dian)池充(chong)電(dian)(dian)的方法

　　多種輸入源

　　用(yong)(yong)(yong)戶(hu)要用(yong)(yong)(yong)多種輸入源(yuan)給電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)有(you)(you)幾個(ge)原(yuan)(yuan)因(yin)。有(you)(you)些應用(yong)(yong)(yong)也許需(xu)要擺(bai)脫電(dian)(dian)(dian)(dian)(dian)(dian)網(wang)的(de)束縛(fu)，而(er)靠(kao)太(tai)陽(yang)能電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)板(ban)供電(dian)(dian)(dian)(dian)(dian)(dian)。另(ling)一(yi)些應用(yong)(yong)(yong)則(ze)可能要求(qiu)能方便(bian)地用(yong)(yong)(yong)交流適配(pei)器(qi)(qi)、汽車電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)或高(gao)壓(ya)工業及電(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。無(wu)論(lun)出于何(he)種原(yuan)(yuan)因(yin)，這要求(qiu)都(dou)(dou)給電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)系統增(zeng)加了極(ji)大的(de)負擔。大多數(shu)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)都(dou)(dou)利(li)用(yong)(yong)(yong)降壓(ya)型(開關或線(xian)性)架構，用(yong)(yong)(yong)高(gao)于電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)最高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)源(yuan)給電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。以(yi)前(qian)的(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)產(chan)品輸入電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)一(yi)般限制(zhi)(zhi)為(wei)大約30V。這樣的(de)限制(zhi)(zhi)使(shi)(shi)設計師無(wu)法(fa)將電(dian)(dian)(dian)(dian)(dian)(dian)信電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)或者具(ju)42V開路電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)太(tai)陽(yang)能電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)板(ban)作為(wei)可行的(de)輸入電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)。在有(you)(you)些情(qing)況下，希(xi)望使(shi)(shi)用(yong)(yong)(yong)的(de)輸入電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)涵蓋了高(gao)于和低于電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)范圍(wei)。設計一(yi)款應對(dui)此類難(nan)題的(de)解(jie)決方案通常(chang)需(xu)要混合使(shi)(shi)用(yong)(yong)(yong)高(gao)精度的(de)電(dian)(dian)(dian)(dian)(dian)(dian)流檢測放大器(qi)(qi)、ADC、一(yi)個(ge)用(yong)(yong)(yong)于控制(zhi)(zhi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)微處理器(qi)(qi)、一(yi)個(ge)高(gao)性能DC/DC轉換器(qi)(qi)以(yi)及一(yi)個(ge)理想二(er)極(ji)管或多路復用(yong)(yong)(yong)電(dian)(dian)(dian)(dian)(dian)(dian)路。

　　強大的(de)充(chong)電解決方案提供(gong)無與倫比的(de)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LTC4000驅動的(de)(de)(de)典型(xing)(xing)DC/DC轉換(huan)器(qi)拓(tuo)撲包(bao)括(kuo)但不(bu)限于(yu)：降壓、升(sheng)壓、降壓-升(sheng)壓、SEPIC和反(fan)激式拓(tuo)撲。該器(qi)件(jian)提供精(jing)確(que)的(de)(de)(de)輸(shu)(shu)入和充電(dian)(dian)電(dian)(dian)流調節，在3V至60V的(de)(de)(de)寬輸(shu)(shu)入和輸(shu)(shu)出(chu)電(dian)(dian)壓范圍內工(gong)作，實現(xian)了與各種不(bu)同的(de)(de)(de)輸(shu)(shu)入電(dian)(dian)壓源、以及(ji)不(bu)同尺寸和化(hua)學(xue)組成的(de)(de)(de)電(dian)(dian)池(chi)(chi)組的(de)(de)(de)兼容性。由于(yu)該器(qi)件(jian)的(de)(de)(de)通用型(xing)(xing)配置，因此(ci)其典型(xing)(xing)應用十分廣泛，包(bao)括(kuo)高(gao)功率(lv)電(dian)(dian)池(chi)(chi)充電(dian)(dian)器(qi)系(xi)統、高(gao)性能便攜式儀器(qi)、電(dian)(dian)池(chi)(chi)后備系(xi)統、配有工(gong)業電(dian)(dian)池(chi)(chi)的(de)(de)(de)設備以及(ji)筆記(ji)本/小型(xing)(xing)筆記(ji)本電(dian)(dian)腦。

　　除了(le)(le)可(ke)以與(yu)(yu)很多不同的(de)DC/DC拓(tuo)撲(pu)結合(he)，LTC4000的(de)高壓能力還允許(xu)該(gai)器件構(gou)成強大(da)和(he)幾乎可(ke)使用(yong)任何(he)輸(shu)入電(dian)(dian)(dian)源(參(can)見圖(tu)4和(he)圖(tu)5)的(de)電(dian)(dian)(dian)池充電(dian)(dian)(dian)解決方案。為了(le)(le)確(que)保(bao)(bao)來自這些輸(shu)入的(de)功率(lv)傳送(song)給合(he)適(shi)的(de)負(fu)載，LTC4000采用(yong)了(le)(le)一種智能電(dian)(dian)(dian)源通路(lu)拓(tuo)撲(pu)，當輸(shu)入功率(lv)有限時(shi)，該(gai)拓(tuo)撲(pu)可(ke)優(you)先為系(xi)統(tong)負(fu)載供電(dian)(dian)(dian)。LTC4000控制外(wai)部(bu)PFET，以提供低(di)損(sun)耗反向電(dian)(dian)(dian)流(liu)(liu)保(bao)(bao)護、電(dian)(dian)(dian)池的(de)低(di)損(sun)耗充電(dian)(dian)(dian)和(he)放(fang)電(dian)(dian)(dian)以及即(ji)(ji)時(shi)接通工(gong)作，這樣(yang)就可(ke)以確(que)保(bao)(bao)即(ji)(ji)使在電(dian)(dian)(dian)池沒電(dian)(dian)(dian)或(huo)深度放(fang)電(dian)(dian)(dian)時(shi)，當一插上電(dian)(dian)(dian)源，系(xi)統(tong)電(dian)(dian)(dian)源就能立(li)即(ji)(ji)可(ke)用(yong)。外(wai)部(bu)檢測電(dian)(dian)(dian)阻器提供輸(shu)入電(dian)(dian)(dian)流(liu)(liu)和(he)電(dian)(dian)(dian)池充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)信息(xi)，從而使LTC4000能與(yu)(yu)涵蓋mW至kW功率(lv)范圍的(de)轉換(huan)器一起使用(yong)。

　　LTC4000的(de)全功能電(dian)(dian)(dian)池(chi)(chi)充電(dian)(dian)(dian)控制器可為各種化學組成的(de)電(dian)(dian)(dian)池(chi)(chi)充電(dian)(dian)(dian)，包括鋰(li)離子/聚(ju)合物/磷酸(suan)、密封鉛酸(suan)(SLA)和鎳化學組成。該(gai)電(dian)(dian)(dian)池(chi)(chi)充電(dian)(dian)(dian)器還(huan)提供(gong)精確的(de)電(dian)(dian)(dian)流(liu)檢(jian)測功能，從而在(zai)大(da)電(dian)(dian)(dian)流(liu)應用情況下允(yun)許較低的(de)檢(jian)測電(dian)(dian)(dian)壓。

　　結論

　　新式(shi)便(bian)攜(xie)式(shi)產品設(she)(she)計師的(de)(de)工(gong)作極富(fu)挑戰性(xing)(xing)，尤其是(shi)涉(she)及到電源(yuan)(yuan)時(shi)。客戶不斷(duan)要(yao)求更多(duo)功能(neng)以導致(zhi)需要(yao)更大(da)的(de)(de)功率，結(jie)果是(shi)電池(chi)(chi)越來越大(da)。同時(shi)，客戶希望可(ke)(ke)方(fang)便(bian)地(di)用幾乎任何可(ke)(ke)用的(de)(de)電源(yuan)(yuan)給這些電池(chi)(chi)充電。盡(jin)管便(bian)攜(xie)式(shi)電源(yuan)(yuan)領(ling)域的(de)(de)這些趨勢造成了設(she)(she)計挑戰，但是(shi)LTC4155和LTC4000讓(rang)設(she)(she)計工(gong)作變得簡單多(duo)了。在低壓系統(tong)中，LTC4155高效率地(di)提供高達3.5A的(de)(de)充電電流，而且提供很多(duo)高性(xing)(xing)能(neng)功能(neng)。LTC4000可(ke)(ke)構成強大(da)的(de)(de)充電解決方(fang)案，而且幾乎可(ke)(ke)使用任何輸入，從而提供了無與(yu)倫比的(de)(de)性(xing)(xing)能(neng)和靈活性(xing)(xing)。