ng-required validation not working on daterange picker

i’m using daterange picker to take date input in ng-repeat but somehow ng-required on picker is not working. form gets submitted without field input

<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.4.7/angular.min.js"></script>
<div class="input-group date-picker input-daterange"data-date-format="yyyy-mm-dd">
   <input type="text" ng-change="onValidateSaleDate(temp_loop.season_fromdate,temp_loop.season_todate,temp_loop.stop_sale)"
                                                id="stop_sale" datepicker readonly autocomplete="off"
                                                class="form-control input-lg date-bg" name="stop_sale_{{season_index}}"
                                                ng-required="true" ng-model="temp_loop.stop_sale" placeholder="Date">
                                            <span class="input-group-btn" ng-click="openDatePicker('stop_sale')">
                                                <button class="btn default btn-lg" type="button">
                                                    <i class="fa fa-calendar"></i>
                                                </button>
                                            </span>
                                        </div>

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Source Url ng-required validation not working on daterange picker