Simply add the ng-required directive to all fields in myForm.
E.g. <input type="text" name="myInput" ng-required="isRequired()" />.
The isRequired function should then simply return true if at least one of the form fields contains a value, otherwise false.
If this doesn't work, then there's information you've left out - so in that case please provide more information about your HTML and JS code (I'm only mentioning this because I see you've tagged the question with ng-repeat, which might make the scenario slightly different than the vanilla one you've described in your question).