I have a simple test application where I'm trying to get the Ext.device.filesystem.Cordova API to work. I'm using the Sencha architect simulate on IOS to preview the application. I keep getting the following error :

Code:
[Error] TypeError: 'undefined' is not a function (evaluating 'b.download({source:a,success:function(c){console.log(c)},failure:function(c){console.log(c)}})')
    downloadFile (app.js, line 1)
    onButtonTap (app.js, line 1)
    doFire (app.js, line 1)
    fire (app.js, line 1)
    doDispatchEvent (app.js, line 1)
    dispatch (app.js, line 1)
    publish (app.js, line 1)
    doFire (app.js, line 1)
    fire (app.js, line 1)
    doDispatchEvent (app.js, line 1)
    dispatchEvent (app.js, line 1)
    doFireEvent (app.js, line 1)
    fireAction (app.js, line 1)
    onTap (app.js, line 1)
    doFire (app.js, line 1)
    fire (app.js, line 1)
    doDispatchEvent (app.js, line 1)
    dispatch (app.js, line 1)
    callParent (app.js, line 1)
    dispatch (app.js, line 1)
    doPublish (app.js, line 1)
    publish (app.js, line 1)
    callSuper (app.js, line 1)
    publish (app.js, line 1)
    onRecognized (app.js, line 1)
    fire (app.js, line 1)
    onTouchEnd (app.js, line 1)
    invokeRecognizers (app.js, line 1)
    onTouchEnd (app.js, line 1)
    onEvent (app.js, line 1)
    (anonymous function) (app.js, line 1)
Controller:

Code:
Ext.define('cordovatest.controller.DeviceFileSystemController', {
    extend: 'Ext.app.Controller',

    requires: [
        'Ext.device.filesystem.Cordova',
        'Ext.device.FileSystem'
    ],

    config: {
        control: {
            "button#mybutton": {
                tap: 'onButtonTap'
            }
        }
    },

    onButtonTap: function(button, e, eOpts) {
        this.downloadFile("http://my/url");
    },

    downloadFile: function(url) {
        var fsys = new Ext.device.filesystem.Cordova();

        fsys.download({
            source: url,
            success: function(entry){
                console.log(entry);
            },
            failure: function(error){
                console.log(error);
            }
        });

    }

});
Any advice?