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(chao)便攜PC (UMPC) 擁有(you)(you)一(yi)個功能(neng)(neng)強大(da)的處理器(qi)(qi)，擁有(you)(you)一(yi)個 具有(you)(you)觸摸功能(neng)(neng)的4～7英寸(cun)的顯示屏，可以運行與Windows Vista兼容的軟件。超(chao)便攜 PC 還擁有(you)(you)全球定位系統 (GPS) 設備、指紋(wen)識別器(qi)(qi)、TV 調諧(xie)器(qi)(qi)以及(ji)存(cun)儲卡讀卡器(qi)(qi)等(deng)。它由2～3 塊串聯鋰(li)離子(zi)電池組供電。

　　移動互聯(lian)網(wang)設(she)備 (MID) 是一種具有多媒體(ti)功能的(de)手持式(shi)電(dian)(dian)腦，可以(yi)提供無(wu)線網(wang)絡(luo)訪問，具有雙向通(tong)信和實(shi)時共享功能，專為向個(ge)人(ren)（非企業用戶）提供娛樂、資訊和定位服務而(er)設(she)計。MID 的(de)外(wai)形尺寸(cun)比智能電(dian)(dian)話大(da)，但比 UMPC 小，通(tong)常使(shi)用一個(ge)鋰(li)離子電(dian)(dian)池(chi)組供電(dian)(dian)。

　　動態電源管理

　　電池充電電壓和電(dian)流對電(dian)池使用(yong)壽命和電(dian)池容量至關重要(yao)。電(dian)池充電(dian)電(dian)壓越(yue)高，電(dian)池容量也就越(yue)高。這些便攜設備因(yin)其微處(chu)理(li)器(qi)功(gong)耗(hao)很低，需要(yao)的(de)總功(gong)耗(hao)低于(yu)筆記本電(dian)腦，所用(yong)的(de)電(dian)源適(shi)配器(qi)功(gong)率一般在(zai) 40 瓦以下，而筆記本電(dian)腦通常使用(yong) 60 瓦和 90 瓦的(de)適(shi)配器(qi)。但是，仍然要(yao)求(qiu)這種適(shi)配器(qi)在(zai)給電(dian)池充電(dian)的(de)同時為系統供(gong)電(dian)，從而最(zui)小(xiao)化適(shi)配器(qi)額定功(gong)率。由(you)于(yu)微處(chu)理(li)器(qi)的(de)高脈動功(gong)率特性，電(dian)池充電(dian)以及(ji)為微處(chu)理(li)器(qi)提供(gong)最(zui)大功(gong)率所要(yao)求(qiu)的(de)總功(gong)率輕易便超(chao)出了適(shi)配器(qi)的(de)最(zui)大可用(yong)功(gong)率。

　　為了優化系統和電池充電器，我(wo)們通過引(yin)入(ru)(ru)最大(da)適配(pei)器(qi)電(dian)(dian)(dian)(dian)(dian)流(liu)調(diao)節(jie)環路使用(yong)了動(dong)態電(dian)(dian)(dian)(dian)(dian)源(yuan)管(guan)理(li) (DPM) 功能(neng)。如果輸(shu)(shu)入(ru)(ru)適配(pei)器(qi)電(dian)(dian)(dian)(dian)(dian)流(liu)達(da)到了調(diao)節(jie)閾值，則電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)自(zi)(zi)動(dong)降低有效充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)，同(tong)時(shi)優先為系統供電(dian)(dian)(dian)(dian)(dian)，以使其不超出適配(pei)器(qi)的最大(da)功率極限。在為系統供電(dian)(dian)(dian)(dian)(dian)以后，剩余功率用(yong)于對電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)。一(yi)旦脈沖功率終(zhong)止(zhi)，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)便自(zi)(zi)動(dong)恢復最快充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)模(mo)式，以縮短(duan)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)間（圖1）。一(yi)種重(zhong)要的規(gui)范是輸(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)流(liu)調(diao)節(jie)精度。輸(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)流(liu)調(diao)節(jie)精度越高，適配(pei)器(qi)提供的功率越多，同(tong)時(shi)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)的速度也就越快。

圖 1  動態電(dian)源管理的電(dian)池充電(dian)結構(gou)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。如果出現(xian)逆向適配器電壓，也(ye)不(bu)能開(kai)啟系(xi)統。

　　b、電池充電安全性

　　在(zai)極(ji)(ji)低或極(ji)(ji)高(gao)電(dian)(dian)池(chi)(chi)(chi)溫(wen)度條(tiao)件下對鋰(li)離子電(dian)(dian)池(chi)(chi)(chi)充電(dian)(dian)是很危(wei)險的。當電(dian)(dian)池(chi)(chi)(chi)在(zai)4.3V溫(wen)度達到 175oC 時，LiCoO2 負(fu)極(ji)(ji)材料的鋰(li)離子電(dian)(dian)池(chi)(chi)(chi)可能會(hui)(hui)爆(bao)炸。已發(fa)布的許(xu)多工業(ye)電(dian)(dian)池(chi)(chi)(chi)充電(dian)(dian)器(qi)安全(quan)規定（例如：日本電(dian)(dian)子和信息技術行業(ye)協會(hui)(hui) (JEITA) 等）通(tong)過(guo)減(jian)少低或高(gao)電(dian)(dian)池(chi)(chi)(chi)溫(wen)度下的電(dian)(dian)池(chi)(chi)(chi)充電(dian)(dian)電(dian)(dian)流和電(dian)(dian)壓來達到電(dian)(dian)池(chi)(chi)(chi)安全(quan)充電(dian)(dian)的目的。

　　要開始充(chong)電(dian)(dian)(dian)過程，一(yi)(yi)般電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)溫度(du)范圍在 0oC ～40oC 之間。因此，必須通過電(dian)(dian)(dian)量監測計或(huo)充(chong)電(dian)(dian)(dian)器(qi)來(lai)監測電(dian)(dian)(dian)池溫度(du)。電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)系(xi)統失效(xiao)時(shi)，安全(quan)定(ding)時(shi)器(qi)是(shi)另一(yi)(yi)層保護。當安全(quan)定(ding)時(shi)器(qi)終止時(shi)，電(dian)(dian)(dian)池便停止充(chong)電(dian)(dian)(dian)。

　　c、電池充電器輸出短路和過充電流保護

　　對于一些計算應用來(lai)說，最為常(chang)用的鋰離子(zi)電(dian)池是(shi)具有(you)(you) 2200-2600mAh 容量的 18650 鋰離子(zi)電(dian)池。12-V 或 19-V 適(shi)配器(qi)在 0.7oC 充(chong)(chong)電(dian)率情況下，充(chong)(chong)電(dian)電(dian)流約為 2-4A。高效充(chong)(chong)電(dian)要求(qiu)同步開關(guan)降壓型拓撲。其還要求(qiu)在出現元件故(gu)障(zhang)或非正常(chang)運行(xing)狀態（例(li)如：充(chong)(chong)電(dian)器(qi)輸出短路或電(dian)感短路等(deng)）時有(you)(you)一個無煙充(chong)(chong)電(dian)系統。充(chong)(chong)電(dian)器(qi)需要有(you)(you)此類保護機制來(lai)防止起火(huo)或冒(mao)煙。

　　上網本、UMPC 和 MID 的電池充電器解決方案

　　根據系統優(you)化和安全(quan)(quan)要求(qiu)，圖2顯(xian)示(shi)了一款適用(yong)于(yu)上(shang)網本應用(yong)且(qie)具有動(dong)態電(dian)(dian)(dian)源管理功能的(de)(de)獨立型高效(xiao)同步開(kai)關(guan)鋰離子(zi)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)器(qi)(qi)。這種(zhong)設(she)計示(shi)例(li)使用(yong)200mA預充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流和2A快速充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流以(yi)及 3 小時(shi)安全(quan)(quan)定時(shi)器(qi)(qi)來對2節鋰離子(zi)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)。通過(guo)監測輸入電(dian)(dian)(dian)流感應電(dian)(dian)(dian)阻R1兩端的(de)(de)壓(ya)(ya)降(jiang)實(shi)現DPM功能。同步開(kai)關(guan)充(chong)電(dian)(dian)(dian)器(qi)(qi)以(yi)600kHz 的(de)(de)開(kai)關(guan)頻率(lv)工作，以(yi)優(you)化效(xiao)率(lv)和解決(jue)方案尺寸。外部(bu)電(dian)(dian)(dian)阻分壓(ya)(ya)器(qi)(qi)R11和R12用(yong)于(yu)設(she)置理想的(de)(de)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)(ya)。要想獲得最大的(de)(de)電(dian)(dian)(dian)池(chi)容量，請將外部(bu)電(dian)(dian)(dian)阻分壓(ya)(ya)器(qi)(qi)設(she)置為每節電(dian)(dian)(dian)池(chi) 4.2V 的(de)(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)(ya)。

　　如(ru)欲獲得最長電池(chi)(chi)使用壽命，請將(jiang)(jiang)電池(chi)(chi)充(chong)電電壓設置(zhi)為每節電池(chi)(chi)4.1V。通過讓外部功率 MOSFET 適合于許多沒(mei)有主控制器的不同電池(chi)(chi)充(chong)電應用，這種(zhong)情(qing)況(kuang)可以(yi)將(jiang)(jiang)1到6節鋰(li)離子串聯電池(chi)(chi)充(chong)至10A。其(qi)還擁(yong)有其(qi)他保護功能，例如(ru)：輸入(ru)過壓、電池(chi)(chi)充(chong)電過壓、電池(chi)(chi)短路、過充(chong)電電流保護等(deng)，并自(zi)動監測電池(chi)(chi)溫(wen)度，以(yi)達到安全充(chong)電的目(mu)的。

圖2 上網本充(chong)電器設計(ji)實例

　　隨著便攜式計(ji)算設備的(de)(de)發展，其擁有(you)了更(geng)多(duo)的(de)(de)特性，這(zhe)時電池(chi)充(chong)電和系統設計(ji)便成為獲得高(gao)安全和高(gao)性能系統最(zui)重要(yao)的(de)(de)設計(ji)因素(su)。