Doctrine 2 / Codeigniter 2.2 - 无法捕获PDOException

I'm pretty new in Doctrine and i've a problem. I install Doctrine 2 with CodeIgniter. Here is my class to call Doctrine in CodeIgniter:

<?php

use Doctrine\Common\ClassLoader;

class Doctrine
{
    public $conn;

    public function __construct()
    {
        try 
        {
            require_once APPPATH . '/third_party/Doctrine/Common/ClassLoader.php';

            $classLoader = new ClassLoader('Doctrine', APPPATH . 'third_party' );
            $classLoader->register();

            $config = new \Doctrine\DBAL\Configuration();
            $connectionParams = array(
                'dbname' => 'mydb',
                'user' => 'user',
                'password' => 'secret',
                'host' => 'localhost',
                'driver' => 'pdo_mysql'
            );



            $this->conn = \Doctrine\DBAL\DriverManager::getConnection($connectionParams, $config);

        } catch (\PDOException $e){
            echo 'An error as ocurred...';

        } catch (Exception $ex) {
            echo 'ERROR';
        }

    }

The config parameters are wrong, with the porpose to throw an excpetion, in this case a PDOException. But to my surprise, insted I get the message

"An error as ocurred..." i get "Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000] [1045] Access denied for user 'user'(...)"

I try the catch with \PDOException or PDOException and can't catch the exception....

Can someone help me?