一、概述

LDO，全稱為(wei)“Low Dropout Regulator”，是一種(zhong)低壓(ya)(ya)(ya)差(cha)線性(xing)穩壓(ya)(ya)(ya)元(yuan)(yuan)器(qi)(qi)件。其(qi)工作原理為(wei)，使用在其(qi)飽和區域內運行的(de)(de)晶體管或場(chang)效應管（FET），從應用的(de)(de)輸(shu)入(ru)電(dian)(dian)(dian)壓(ya)(ya)(ya)中(zhong)減去超額(e)的(de)(de)電(dian)(dian)(dian)壓(ya)(ya)(ya)，產生經(jing)過調節的(de)(de)輸(shu)出(chu)電(dian)(dian)(dian)壓(ya)(ya)(ya)。相比于傳統的(de)(de)DC-DC變換器(qi)(qi)，LDO具有成本低，噪音低，靜態電(dian)(dian)(dian)流小的(de)(de)特點，需要的(de)(de)外(wai)接元(yuan)(yuan)件也很少，因此,LDO廣(guang)泛(fan)應用于需要穩壓(ya)(ya)(ya)輸(shu)出(chu)的(de)(de)場(chang)景。

（UTC78XX系(xi)列(lie)LDO封裝以及內部電路示意圖）

（普賽斯(si)S系列源表）                              （UTC7805 LDO電參(can)數規格書(shu)）

源(yuan)(yuan)(yuan)(yuan)表(biao)(biao)(biao)(biao)，SMU(Source Measure Unit)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)/測(ce)量(liang)(liang)單(dan)元，“源(yuan)(yuan)(yuan)(yuan)”為電(dian)(dian)(dian)壓(ya)源(yuan)(yuan)(yuan)(yuan)和電(dian)(dian)(dian)流(liu)(liu)源(yuan)(yuan)(yuan)(yuan)，“表(biao)(biao)(biao)(biao)”為測(ce)量(liang)(liang)表(biao)(biao)(biao)(biao)，“源(yuan)(yuan)(yuan)(yuan)表(biao)(biao)(biao)(biao)”即指一種可(ke)(ke)作(zuo)為四(si)象限的電(dian)(dian)(dian)壓(ya)源(yuan)(yuan)(yuan)(yuan)或電(dian)(dian)(dian)流(liu)(liu)源(yuan)(yuan)(yuan)(yuan)提供(gong)精確的電(dian)(dian)(dian)壓(ya)或電(dian)(dian)(dian)流(liu)(liu)，同時可(ke)(ke)同步測(ce)量(liang)(liang)電(dian)(dian)(dian)流(liu)(liu)值或電(dian)(dian)(dian)壓(ya)值的測(ce)量(liang)(liang)儀表(biao)(biao)(biao)(biao)。普賽斯S系列(lie)高精度(du)源(yuan)(yuan)(yuan)(yuan)表(biao)(biao)(biao)(biao)，集電(dian)(dian)(dian)壓(ya)、電(dian)(dian)(dian)流(liu)(liu)輸(shu)(shu)入輸(shu)(shu)出及測(ce)量(liang)(liang)等多種功(gong)能(neng)于一體。產品(pin)更(geng)(geng)大輸(shu)(shu)出電(dian)(dian)(dian)壓(ya)達300V，更(geng)(geng)小測(ce)試電(dian)(dian)(dian)流(liu)(liu)量(liang)(liang)程(cheng)低(di)至(zhi)100pA，支持四(si)象限工作(zuo)，因此,可(ke)(ke)廣(guang)泛應用于LDO類芯片測(ce)試。

二、常用電性能參數測試

LDO常用(yong)的電性能參數(shu)測(ce)試，主(zhu)要包(bao)括輸(shu)出電壓、輸(shu)入(ru)輸(shu)出電壓差、線(xian)性調整(zheng)率、負(fu)載調整(zheng)率、靜態(tai)電流等。由于LDO的測(ce)試需要分別采集輸(shu)入(ru)與輸(shu)出端(duan)的數(shu)據，因此一般情況下(xia)，測(ce)試系統(tong)至(zhi)少需要配置2臺SMU，并采用(yong)上位機軟件(PssSMUTools)進行控制。（以下(xia)測(ce)試均參考(kao)UTC7805規格進行）

                                                                           （二線法連接示意圖）

                                                                           （四線(xian)法連(lian)接示(shi)意(yi)圖）

三、測試方案

? Vo輸出電壓測試

Vo輸(shu)出(chu)電(dian)(dian)壓(ya)(ya)，是(shi)LDO在正常(chang)工作下的(de)穩定(ding)輸(shu)出(chu)電(dian)(dian)壓(ya)(ya)值。當加載在LDO輸(shu)入端(duan)(duan)的(de)工作電(dian)(dian)壓(ya)(ya)，在規定(ding)范(fan)圍內變動時，LDO的(de)輸(shu)出(chu)電(dian)(dian)壓(ya)(ya)Vo穩定(ding)在特定(ding)范(fan)圍內。常(chang)用測(ce)試方(fang)法(fa)為，在LDO的(de)輸(shu)入端(duan)(duan)，加載穩定(ding)變化的(de)電(dian)(dian)壓(ya)(ya)，同時測(ce)量對應的(de)輸(shu)出(chu)端(duan)(duan)電(dian)(dian)壓(ya)(ya)值。一般采用二線(xian)法(fa)連接即可。（參考UTC7805規格書，其(qi)規格參數5V左右）

操作步驟

? Voi輸入輸出電壓差，ΔVo線性調整率測試

Voi輸(shu)(shu)(shu)入輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)差，是(shi)LDO正(zheng)常工作時輸(shu)(shu)(shu)入端(duan)與輸(shu)(shu)(shu)出(chu)端(duan)的更小電(dian)(dian)(dian)(dian)壓(ya)(ya)差值(zhi)。ΔVo線性調(diao)整(zheng)率(lv)是(shi)輸(shu)(shu)(shu)入電(dian)(dian)(dian)(dian)壓(ya)(ya)變(bian)(bian)化后對輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)造成的影(ying)響。常用(yong)(yong)測(ce)(ce)試(shi)方法為(wei)(wei)，在LDO的輸(shu)(shu)(shu)入端(duan)，加(jia)載(zai)穩定變(bian)(bian)化的電(dian)(dian)(dian)(dian)壓(ya)(ya)，同時測(ce)(ce)量對應的輸(shu)(shu)(shu)出(chu)端(duan)電(dian)(dian)(dian)(dian)壓(ya)(ya)值(zhi)，并計算(suan)兩端(duan)電(dian)(dian)(dian)(dian)壓(ya)(ya)測(ce)(ce)差值(zhi)，或者輸(shu)(shu)(shu)出(chu)端(duan)的變(bian)(bian)化值(zhi)。此外，為(wei)(wei)降低測(ce)(ce)試(shi)中線材的干擾(rao)，輸(shu)(shu)(shu)入輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)差測(ce)(ce)試(shi)可采用(yong)(yong)4線連(lian)接法進行測(ce)(ce)量。（參(can)考UTC7805規格書(shu)，Voi值(zhi)為(wei)(wei)2V左(zuo)右,ΔVo值(zhi)為(wei)(wei)4mV左(zuo)右）

操作步驟

? ΔVoload負載(zai)調整率(lv)測試

ΔVoload負載(zai)調整率是輸(shu)(shu)(shu)出(chu)端(duan)接(jie)不(bu)同(tong)負載(zai)，輸(shu)(shu)(shu)出(chu)端(duan)電(dian)壓的(de)變化(hua)。由(you)于源表可以直接(jie)當電(dian)子負載(zai)，所以可以直接(jie)讓源表做負載(zai)。常用測(ce)試(shi)方法(fa)為，保持LDO輸(shu)(shu)(shu)入端(duan)電(dian)壓穩定不(bu)變，在LDO的(de)輸(shu)(shu)(shu)出(chu)端(duan)，加載(zai)不(bu)同(tong)的(de)電(dian)流值(zhi)，同(tong)時測(ce)量(liang)(liang)對應的(de)輸(shu)(shu)(shu)出(chu)端(duan)電(dian)壓值(zhi)，并計(ji)算輸(shu)(shu)(shu)出(chu)端(duan)的(de)電(dian)壓變化(hua)值(zhi)。此外，為降低測(ce)試(shi)中線材的(de)干擾(rao)，該測(ce)試(shi)可采用4線連接(jie)法(fa)進行測(ce)量(liang)(liang)。（參考(kao)UTC7805規格書，ΔVoload值(zhi)為4mV左右(you)）

操作步驟

? IQ靜態電(dian)流測(ce)試(shi)測(ce)試(shi)

IQ靜態電(dian)(dian)(dian)流(liu)，是指輸出端(duan)(duan)空載時，輸入(ru)端(duan)(duan)流(liu)進(jin)的電(dian)(dian)(dian)流(liu)。常用測(ce)試方法為，斷開LDO的輸出端(duan)(duan)的連接，加載不同的電(dian)(dian)(dian)流(liu)值(zhi)，在LDO輸入(ru)端(duan)(duan)加載電(dian)(dian)(dian)壓，并測(ce)量對應的輸入(ru)端(duan)(duan)電(dian)(dian)(dian)流(liu)值(zhi)。（參考(kao)UTC7805規格(ge)書，IQ值(zhi)為5mA左右(you)）