Recursively convert PHP Array into XML?

I am working on a RESTful API serving content in three modes viz., JSON [most of the times], HTML [when non-api calls are made] and XML [legacy support].

My controllers return PHP arrays and then in the Views, I convert them into the desired output. PHP to JSON is done via json_encode, PHP to HTML is done via message passing between Views and Template Engine. Now, I am writing a recursive function to handle multi-dimensional PHP arrays and convert them into well formatted XML.

Following is my function:

function recursive_xml($array, \SimpleXMLElement $xmlObj){
    foreach($array as $key=>$value){
        $xmlObj->addChild($key);
        if(!is_array($value)){
            $xmlObj->$key = $value;
        }
        else { //Value is array
            recursive_xml($value, $xmlObj->$key);
        }
    }
    header('Content-type: text/xml');
    echo $xmlObj->asXML();
} //End recursive_xml

This is working almost 80% as expected, going through arrays and creating the XML output. But the funny problem is that in the second call of the recursive_xml and there after, it appends the output in the XML and ALSO before the XML decalaration. Let's take a test case:

$obj = new \SimpleXMLElement("<root />");
$array = array("a"=>"b", "c"=>"d", "e"=>array("x"=>"z", "y"=>"v")); 
recursive_xml($array, $obj);

Now the output:

 `<e><x>z</x><y>v</y></e><?xml version="1.0"?>
 <root><a>b</a><c>d</c><e><x>z</x><y>v</y></e></root>`

The second line of the output along with the XML declaration is what I would be ideally looking for. Any help will be deeply appreciated!