Angular CheckBox JS Questions

I have a small catch in my application, I have a Grid with check-box and a check-box to mark all . I want a function that unchecks the check-box that marks all when you do not have all grid check boxes checked.

<table>
    <thead>
        <tr>
            <th><input type="checkBox" ng-model="chkMarcaTodos"/></th>
            <th>Nome</th>
            <th>Telefone</th>
        </tr>
    </thead>
    <tbody>
        <tr ng-repeat="cad in cadastros track by $index">
            <td><input type="checkBox" ng-model="cad.selecionado"/></td>
            <td>{{cad.nome}}</td>
            <td>{{cad.telefone}}</td>
        </tr>
    </tbody>
</table>

  

Completing [...]

I want the chkMarcaTodos to be marked if all the selected chars are checked and the chkMarcaTodos is cleared if any selected chars are deselected.