針對手機應用改良電池充電器IC的設計原理
我(wo)們現(xian)在處于(yu)(yu)一個(ge)全球無線互聯的時代,幾乎(hu)沒(mei)有什么比時刻保(bao)持手機(ji)或移動上網(wang)設(she)(she)備處于(yu)(yu)通電(dian)(dian)(dian)狀(zhuang)態來(lai)的重要。隨著便(bian)攜式(shi)和手持式(shi)設(she)(she)備上的功(gong)(gong)能不(bu)斷擴展,電(dian)(dian)(dian)池(chi)(chi)充電(dian)(dian)(dian)器IC的設(she)(she)計人員也(ye)面臨(lin)嚴峻的考驗。高分辨率(lv)屏幕,更大的存儲能力以及設(she)(she)備上的新(xin)功(gong)(gong)能都(dou)增加了電(dian)(dian)(dian)池(chi)(chi)的負荷,這不(bu)僅僅需要更好(hao)的電(dian)(dian)(dian)池(chi)(chi)充電(dian)(dian)(dian)技術,而且還需具備高效的電(dian)(dian)(dian)源管理能力。
降低功耗以延長電池壽命,這一直是手持式電源管理的源動力。然而,現在消費者對充電器的充電效率也有所期待,希望能夠縮短設備的充電時間,新一代的充電器設計采用開關充電器替代傳統的線形充電器,除了(le)提供傳(chuan)統線(xian)形(xing)充電(dian)器所(suo)擁有的(de)(de)高(gao)效率之(zhi)外(wai),最大(da)的(de)(de)優勢(shi)就是能(neng)提高(gao)由電(dian)源提供的(de)(de)充電(dian)電(dian)流(liu)。當USB端口斷(duan)電(dian)時(shi),可(ke)用的(de)(de)電(dian)流(liu)被限制在可(ke)能(neng)不到500mA,而此時(shi),這個優勢(shi)就顯得尤為重(zhong)要。更(geng)高(gao)的(de)(de)電(dian)流(liu)意味(wei)著更(geng)短(duan)的(de)(de)充電(dian)時(shi)間,這完全(quan)符合消費者(zhe)的(de)(de)需求。
現在,大多數手持式設備都采用了兩種電池充電器,一種是線性充電器,另一種是開關充電器。線(xian)(xian)性充(chong)(chong)(chong)電(dian)(dian)器(qi)已(yi)有較(jiao)長的(de)(de)歷史,充(chong)(chong)(chong)電(dian)(dian)方式(shi)比較(jiao)簡單有效,噪聲很小,且沒有太多外部元件。但是(shi),隨(sui)著(zhu)便攜式(shi)設備越來越復雜(za),新功能(neng)層出不窮(qiong),高容量電(dian)(dian)池的(de)(de)需(xu)求(qiu)就更加強烈。線(xian)(xian)形充(chong)(chong)(chong)電(dian)(dian)器(qi)的(de)(de)缺點是(shi)功耗太大(da),特別(bie)是(shi)在設備邊充(chong)(chong)(chong)電(dian)(dian)邊使用的(de)(de)時候(hou)尤為明顯,此時產生的(de)(de)熱(re)量可能(neng)損壞系(xi)統或電(dian)(dian)池。
可供選擇的有開關充電器或開關模式電池充電器IC,它(ta)可(ke)以使用盡(jin)可(ke)能少的(de)電(dian)量,為電(dian)池(chi)提供更(geng)高的(de)電(dian)流。從過往經驗來看,這類IC一般會(hui)存(cun)在一些(xie)噪聲問題(ti)。此外,前幾代的(de)開關(guan)式充電(dian)器(qi)還需(xu)要(yao)一些(xie)外部(bu)元件。
然而,開關(guan)式(shi)電(dian)池拓撲結構的(de)(de)優勢(shi)也(ye)是顯(xian)而易見。這些優勢(shi)包括更高(gao)的(de)(de)效率和(he)更低(di)的(de)(de)功耗,還有更短(duan)的(de)(de)充電(dian)時間(jian)。此類(lei)裝(zhuang)置還能利用較高(gao)的(de)(de)輸(shu)入電(dian)壓充電(dian),使用成(cheng)本較低(di)的(de)(de)非穩壓適配器。還可以提高(gao)來自(zi)限流(liu)電(dian)流(liu)源的(de)(de)充電(dian)電(dian)流(liu)。
開關充電器通常在輕負載運行時會產生噪聲,特別是在預處理過程中。隨著噪聲的減少,開關充電器會進入脈沖跳躍(pulse skipping)模式運行。在脈沖跳躍模式中,PWM頻率異步變化。目前開發的電池充電器IC,可(ke)以(yi)在(zai)使用開(kai)(kai)關(guan)充(chong)電(dian)器(qi)(qi)(qi)時(shi)(shi)提供高充(chong)電(dian)電(dian)流(liu),且對(dui)系統(tong)的(de)熱影(ying)響非(fei)常小,而在(zai)低電(dian)流(liu)充(chong)電(dian)模(mo)(mo)式(shi)(shi)(shi)下切換(huan)到線(xian)性(xing)充(chong)電(dian)器(qi)(qi)(qi),以(yi)減(jian)少噪聲(sheng)。這種(zhong)可(ke)提供線(xian)性(xing)模(mo)(mo)式(shi)(shi)(shi)的(de)PWM開(kai)(kai)關(guan)模(mo)(mo)式(shi)(shi)(shi)充(chong)電(dian)器(qi)(qi)(qi)可(ke)以(yi)在(zai)全恒(heng)流(liu)(快(kuai)(kuai)速充(chong)電(dian))條件下實現(xian)高效率。開(kai)(kai)關(guan)充(chong)電(dian)器(qi)(qi)(qi)可(ke)利用PWM開(kai)(kai)關(guan)穩(wen)壓器(qi)(qi)(qi)控制(zhi)高達2A的(de)恒(heng)流(liu)充(chong)電(dian)。當電(dian)池處于(yu)預處理(li)過程以(yi)及恒(heng)壓尖峰(taper)充(chong)電(dian)模(mo)(mo)式(shi)(shi)(shi)快(kuai)(kuai)結(jie)束時(shi)(shi),設備會自動(dong)轉換(huan)到線(xian)形模(mo)(mo)式(shi)(shi)(shi),以(yi)降低噪聲(sheng),并利用開(kai)(kai)關(guan)模(mo)(mo)式(shi)(shi)(shi)加快(kuai)(kuai)充(chong)電(dian)。一(yi)旦(dan)充(chong)電(dian)電(dian)流(liu)值(zhi)低于(yu)300mA,線(xian)性(xing)模(mo)(mo)式(shi)(shi)(shi)會完(wan)全啟動(dong),開(kai)(kai)關(guan)轉換(huan)器(qi)(qi)(qi)產生(sheng)的(de)噪聲(sheng)就(jiu)會消(xiao)除。
但是(shi),現在充(chong)電(dian)(dian)(dian)技術有了進一步的(de)(de)發展。例(li)如,一種用于新型手(shou)持式(shi)設備的(de)(de)單節鋰離子(zi)/聚合物電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)器解決(jue)方案,它的(de)(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流高達1A,具備先進的(de)(de)電(dian)(dian)(dian)充(chong)滿顯示功(gong)能,可以(yi)實現全(quan)程(cheng)(cheng)充(chong)電(dian)(dian)(dian)系統(tong)監(jian)控。符合USB標準的(de)(de)100mA/500mA充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流設置有助于實現可編程(cheng)(cheng)預充(chong)電(dian)(dian)(dian)和快(kuai)速充(chong)電(dian)(dian)(dian)。許多(duo)產品(pin)還(huan)具備電(dian)(dian)(dian)池溫(wen)度監(jian)測(ce)功(gong)能,以(yi)確保安全(quan)充(chong)電(dian)(dian)(dian)。
Intersil等公司正(zheng)在開發新(xin)一代充電(dian)(dian)(dian)器IC技術。這些完全集成的解決方案非常適合緊湊型應用(yong),還能為高(gao)(gao)功率應用(yong)提(ti)供(gong)(gong)充電(dian)(dian)(dian)控制(zhi)功能。目(mu)前(qian),充電(dian)(dian)(dian)電(dian)(dian)(dian)壓精度能達到(dao)0.5%,較前(qian)幾(ji)年的1%有很(hen)大改(gai)善。開關頻率可達3MHz,而且新(xin)型開關充電(dian)(dian)(dian)器可提(ti)供(gong)(gong)高(gao)(gao)達2A的充電(dian)(dian)(dian)電(dian)(dian)(dian)流,最新(xin)的一個應用(yong)實例(li)是ISL9220,它適用(yong)于一節(jie)和兩節(jie)鋰離(li)子電(dian)(dian)(dian)池(chi)應用(yong)。
另外,新設(she)計還可以限制泄漏,目前在沒有加上輸入(ru)功率時,典型的泄漏電(dian)流已低于0.5uA。而且這(zhe)些(xie)改進還可以用于更小(xiao)的封裝,如4mm×4mm QFN或(huo)2mm×2mm CSP,以節省手持式設(she)備的設(she)計空間(jian)。
最新的電池充電器IC還能夠監視(shi)輸(shu)入電(dian)(dian)壓(ya)、電(dian)(dian)池(chi)(chi)電(dian)(dian)壓(ya)和充電(dian)(dian)電(dian)(dian)流。當三個(ge)參數(shu)中任意(yi)一個(ge)超出特定(ding)限額時,該IC就會關(guan)閉內(nei)部N溝(gou)道MOSFET,使充電(dian)(dian)系(xi)統停止(zhi)對電(dian)(dian)池(chi)(chi)充電(dian)(dian)。利用(yong)這(zhe)些重要(yao)(yao)的(de)器件可以靈活(huo)地(di)提高(gao)效率(lv),這(zhe)對持(chi)續增長(chang)、功能不斷(duan)擴充的(de)移動、手持(chi)式產品(pin)是(shi)至關(guan)重要(yao)(yao)的(de)。