小型低成本上網本、超便攜 PC (UMPC) 和移動互聯網設備 (MID) 正變得越來越流行，并得到了用戶的廣泛認可。這些便攜設備中使用的鋰離子 (Li-Ion) 電池充電系統比移動電話中使用的鋰離子電池充電系統要復雜得多。理解其電池充電器的諸多要求成為提高系統安全性的關鍵。本文將討論鋰離子電池充電的許多要求，如：充電系統安全性和充電器與系統之間的性能優化等，還介紹了一個同步開關獨立電池充電器IC控制器設計實例，它擁有動態電源管理功能，用于優化上網本應用的適配器額定功率和對電池快速充電。

　　上網本是小型、輕便和低價筆記本電腦的一種快速衍生品，主要用于一般計算和訪問網絡應用。大多數上網本均使用Intel Atom 微處理器以及2～3塊串聯鋰離子電池組。

　　超便攜PC (UMPC) 擁(yong)有(you)一個(ge)功能(neng)強大的(de)處理(li)器，擁(yong)有(you)一個(ge) 具(ju)有(you)觸摸功能(neng)的(de)4～7英(ying)寸的(de)顯示屏，可以運行與Windows Vista兼容的(de)軟件。超便攜 PC 還擁(yong)有(you)全球定位系統 (GPS) 設備、指紋識別器、TV 調諧(xie)器以及(ji)存儲卡讀卡器等。它由2～3 塊串(chuan)聯鋰離子電(dian)池組供電(dian)。

　　移動互聯網(wang)設備 (MID) 是一種具(ju)有(you)多媒體功(gong)能的(de)手持式電(dian)(dian)(dian)腦，可以提(ti)(ti)供無線網(wang)絡訪問，具(ju)有(you)雙向通(tong)信和(he)實時共享功(gong)能，專為向個人（非企業用(yong)戶）提(ti)(ti)供娛樂(le)、資(zi)訊(xun)和(he)定位服務而設計。MID 的(de)外(wai)形尺寸(cun)比智能電(dian)(dian)(dian)話(hua)大，但比 UMPC 小，通(tong)常使用(yong)一個鋰離子電(dian)(dian)(dian)池組供電(dian)(dian)(dian)。

　　動態電源管理

　　電池充電電壓和(he)電(dian)(dian)(dian)(dian)流對電(dian)(dian)(dian)(dian)池使用壽命和(he)電(dian)(dian)(dian)(dian)池容(rong)量至關重要(yao)。電(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓越高(gao)，電(dian)(dian)(dian)(dian)池容(rong)量也就越高(gao)。這些便攜設備因其(qi)微處(chu)理(li)器(qi)(qi)(qi)功(gong)(gong)耗很(hen)低，需要(yao)的(de)(de)總功(gong)(gong)耗低于筆記(ji)本電(dian)(dian)(dian)(dian)腦(nao)，所用的(de)(de)電(dian)(dian)(dian)(dian)源適(shi)配(pei)器(qi)(qi)(qi)功(gong)(gong)率(lv)一般在 40 瓦(wa)以下，而筆記(ji)本電(dian)(dian)(dian)(dian)腦(nao)通常(chang)使用 60 瓦(wa)和(he) 90 瓦(wa)的(de)(de)適(shi)配(pei)器(qi)(qi)(qi)。但是(shi)，仍然要(yao)求這種適(shi)配(pei)器(qi)(qi)(qi)在給電(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)(de)同(tong)時為系統供電(dian)(dian)(dian)(dian)，從(cong)而最小(xiao)化(hua)適(shi)配(pei)器(qi)(qi)(qi)額定(ding)功(gong)(gong)率(lv)。由于微處(chu)理(li)器(qi)(qi)(qi)的(de)(de)高(gao)脈動(dong)功(gong)(gong)率(lv)特性，電(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)以及為微處(chu)理(li)器(qi)(qi)(qi)提供最大功(gong)(gong)率(lv)所要(yao)求的(de)(de)總功(gong)(gong)率(lv)輕易便超出了適(shi)配(pei)器(qi)(qi)(qi)的(de)(de)最大可用功(gong)(gong)率(lv)。

　　為了優化系統和電池充電器，我(wo)們通過引入(ru)最大適配器(qi)電(dian)(dian)流(liu)(liu)(liu)調節(jie)環路(lu)使用(yong)了動態電(dian)(dian)源(yuan)管理 (DPM) 功能。如果輸(shu)入(ru)適配器(qi)電(dian)(dian)流(liu)(liu)(liu)達到了調節(jie)閾值(zhi)，則電(dian)(dian)池(chi)充(chong)電(dian)(dian)器(qi)自動降(jiang)低有(you)效充(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)(liu)，同(tong)時優先為系統供電(dian)(dian)，以(yi)使其不(bu)超出(chu)適配器(qi)的最大功率極限。在為系統供電(dian)(dian)以(yi)后(hou)，剩余(yu)功率用(yong)于對電(dian)(dian)池(chi)充(chong)電(dian)(dian)。一(yi)旦脈沖功率終止，充(chong)電(dian)(dian)器(qi)便自動恢復最快充(chong)電(dian)(dian)模式，以(yi)縮短充(chong)電(dian)(dian)時間（圖1）。一(yi)種重要的規范是輸(shu)入(ru)電(dian)(dian)流(liu)(liu)(liu)調節(jie)精度。輸(shu)入(ru)電(dian)(dian)流(liu)(liu)(liu)調節(jie)精度越高(gao)，適配器(qi)提(ti)供的功率越多，同(tong)時電(dian)(dian)池(chi)充(chong)電(dian)(dian)的速度也(ye)就(jiu)越快。

圖 1  動態電源管理的電池充電結構圖

　　計算系統和電池充電器安全性

　　a、適配器輸入和電池過壓保護 (OVP)

　　就筆記本電腦而言，一般使用19-V和16-V的適配器，而5-V 適配器則普遍用于智能電話。上網本、UMPC和MID通常使用這些適配器來節省開發成本，但其往往不要求19V 適配器對1到3節串聯電池組充電。此外，IEEE P1725 要求系統包括輸入適配器和電池 OVP。如果這些便攜式設備遇到過輸入電壓，則其會阻止您開啟系統。如果電池過充，則立即關閉電池充電器。如(ru)果(guo)出現逆向(xiang)適配器電壓，也不能(neng)開啟系(xi)統。

　　b、電池充電安全性

　　在極(ji)(ji)低或極(ji)(ji)高電(dian)(dian)池溫(wen)度條(tiao)件下(xia)對鋰離子電(dian)(dian)池充電(dian)(dian)是(shi)很(hen)危險的。當(dang)電(dian)(dian)池在4.3V溫(wen)度達到 175oC 時，LiCoO2 負極(ji)(ji)材料的鋰離子電(dian)(dian)池可(ke)能會(hui)爆(bao)炸。已發布的許(xu)多工(gong)業電(dian)(dian)池充電(dian)(dian)器安全規(gui)定（例如(ru)：日本電(dian)(dian)子和(he)信息技術行業協會(hui) (JEITA) 等）通(tong)過減(jian)少(shao)低或高電(dian)(dian)池溫(wen)度下(xia)的電(dian)(dian)池充電(dian)(dian)電(dian)(dian)流(liu)和(he)電(dian)(dian)壓來達到電(dian)(dian)池安全充電(dian)(dian)的目的。

　　要開始充(chong)電(dian)過程(cheng)，一(yi)般電(dian)池(chi)(chi)充(chong)電(dian)溫度范(fan)圍在 0oC ～40oC 之間。因此，必(bi)須通過電(dian)量監(jian)測計或(huo)充(chong)電(dian)器來監(jian)測電(dian)池(chi)(chi)溫度。電(dian)池(chi)(chi)充(chong)電(dian)系(xi)統失效時(shi)，安全(quan)定時(shi)器是另一(yi)層(ceng)保(bao)護。當(dang)安全(quan)定時(shi)器終止(zhi)時(shi)，電(dian)池(chi)(chi)便停(ting)止(zhi)充(chong)電(dian)。

　　c、電池充電器輸出短路和過充電流保護

　　對于一(yi)些計算(suan)應用來(lai)說，最(zui)為(wei)常(chang)用的鋰離子電(dian)(dian)(dian)池是具有(you) 2200-2600mAh 容量的 18650 鋰離子電(dian)(dian)(dian)池。12-V 或(huo) 19-V 適配器(qi)在 0.7oC 充電(dian)(dian)(dian)率情況下(xia)，充電(dian)(dian)(dian)電(dian)(dian)(dian)流約(yue)為(wei) 2-4A。高效充電(dian)(dian)(dian)要(yao)求同步(bu)開(kai)關降壓型拓撲。其還要(yao)求在出現元件故障或(huo)非正常(chang)運行狀態(tai)（例如(ru)：充電(dian)(dian)(dian)器(qi)輸出短路或(huo)電(dian)(dian)(dian)感(gan)短路等(deng)）時有(you)一(yi)個無煙(yan)(yan)充電(dian)(dian)(dian)系統(tong)。充電(dian)(dian)(dian)器(qi)需要(yao)有(you)此類保護機制來(lai)防止起火或(huo)冒煙(yan)(yan)。

　　上網本、UMPC 和 MID 的電池充電器解決方案

　　根據系統(tong)優(you)化和安(an)全要(yao)求，圖(tu)2顯示(shi)了(le)一款適用于(yu)上網本應用且具有動態電(dian)(dian)(dian)(dian)(dian)源管理功能(neng)的(de)(de)獨立型高效同步開關(guan)鋰(li)離子電(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)。這種(zhong)設計示(shi)例使用200mA預(yu)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流和2A快速充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流以及(ji) 3 小時(shi)安(an)全定(ding)時(shi)器(qi)(qi)來對2節(jie)鋰(li)離子電(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)。通過(guo)監測輸入電(dian)(dian)(dian)(dian)(dian)流感應電(dian)(dian)(dian)(dian)(dian)阻R1兩端的(de)(de)壓(ya)降實現DPM功能(neng)。同步開關(guan)充電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)以600kHz 的(de)(de)開關(guan)頻率(lv)工作，以優(you)化效率(lv)和解決方案尺寸。外部電(dian)(dian)(dian)(dian)(dian)阻分壓(ya)器(qi)(qi)R11和R12用于(yu)設置理想的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓(ya)。要(yao)想獲得(de)最大的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)容量，請將(jiang)外部電(dian)(dian)(dian)(dian)(dian)阻分壓(ya)器(qi)(qi)設置為每節(jie)電(dian)(dian)(dian)(dian)(dian)池(chi) 4.2V 的(de)(de)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓(ya)。

　　如欲獲(huo)得最長電(dian)(dian)(dian)(dian)池(chi)(chi)使用(yong)壽命，請將(jiang)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓設置為每節電(dian)(dian)(dian)(dian)池(chi)(chi)4.1V。通過讓外部功率 MOSFET 適合于(yu)許多沒有(you)主控制器的不(bu)同(tong)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)應用(yong)，這種情況(kuang)可以將(jiang)1到(dao)6節鋰(li)離子串聯電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)至10A。其還擁有(you)其他保護功能，例如：輸入過壓、電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)過壓、電(dian)(dian)(dian)(dian)池(chi)(chi)短(duan)路、過充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流保護等(deng)，并自(zi)動監測電(dian)(dian)(dian)(dian)池(chi)(chi)溫(wen)度，以達到(dao)安全充(chong)(chong)電(dian)(dian)(dian)(dian)的目的。

圖(tu)2 上網本(ben)充(chong)電器設計實(shi)例(li)

　　隨(sui)著便(bian)攜式計算設(she)備的發展，其(qi)擁有了更(geng)多的特(te)性，這時(shi)電池(chi)充電和系(xi)統(tong)設(she)計便(bian)成為獲(huo)得高(gao)安全和高(gao)性能系(xi)統(tong)最重要的設(she)計因(yin)素(su)。