Bootstrap switchand angular initialization

I 've a problem with bootstrap checkbox initialization

<span style="margin-right: 5px;"> </span> 
   <input   type="checkbox" name="accessory"
       data-ng-model="accessory.value" data-ng-attr-id=""
       data-ng-attr-topic="" bootstrap-switch>

ng-model doesn't initialize the status, it is always false. I've tried even with ng-checked="" but nothing is changed. If I use checked or checked="checked" all work fine. Do you have any advice?