Angularjs single select on ng-dropdown-multiselect

I'm new in angularjs and trying to solve the problem. My question is how to make single select from ng-dropdown-multiselect I found some of the solutions like:

vm.dropDownAreaSelection = {
      selectionLimit: '1',
      closeOnSelect: true,
      displayProp: 'name',
      idProp : 'name',
      showCheckAll : false,
      showUncheckAll : false,
      onChange: vm.filterChangedSelection,
      smartButtonMaxItems: 1,
    };

<div ng-dropdown-multiselect
     options="vm.selectArea"
     selected-model="vm.selected.areaObj"
     extra-settings="vm.dropDownAreaSelection"></div>

it's working fine but when I select one item previously selected is not unselected. I'm using angularjs 1.5.3

Any help will be appreciated.

Thanks in advance