overviewMap = new esri.dijit.OverviewMap({ map: _map, expandFactor: 1, maximizeButton:true}, dojo.byId("overviewDiv"));
overviewMap.startup();<div id="ovWin" class="shadow" style="position:absolute; right:3px; bottom:3px; z-Index:998; width:150px;height:150px; "> <div id="overviewDiv" style="width:100%;height:100%;"></div> </div>
//add the overview map
var overviewMapDijit = new esri.dijit.OverviewMap({
map: map,
visible:false,
maximizeButton:true
});
overviewMapDijit.startup();