window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, function (fs) {

    //var absPath = "file:///storage/emulated/0/";
    var absPath = cordova.file.externalRootDirectory;
    var fileDir = cordova.file.externalDataDirectory.replace(cordova.file.externalRootDirectory, '');
    var fileName = "somename.txt";
    var filePath = fileDir + fileName;

    fs.root.getFile(filePath, { create: true, exclusive: false }, function (fileEntry) {
        writeFile(fileEntry, BINARY_ARR).then(function(){
          //do something here
        });
    }, function(err) {});
}, function(err) {});

function writeFile(fileEntry, dataObj) {
    return $q(function (resolve, reject) {
        fileEntry.createWriter(function (fileWriter) {
            fileWriter.onwriteend = function () {
                resolve();
            };
            fileWriter.onerror = function (e) {
                reject(e);
            };
            fileWriter.write(dataObj);
        });
    });
}