Mengkoneksikan database postgre dengan codeigniter

ane biasa pake database phpMysql skrang lg coba koneksi dari database postgres ke Ci tapi ko gak konek, pesannya begini

Access denied for user 'postgres'@'localhost' (using password: YES), please check 'application/config/database.php'.

ini knapaya?

kode di database ane kaya gini

$active_group = 'default';
$query_builder = TRUE;

$db['default'] = array(
	'dsn'	=> '',
	'hostname' => 'localhost',
	'username' => 'nama usr',
	'password' => 'disini_passwd',
	'database' => 'db_ci',
	'dbdriver' => 'postgre',
	'dbprefix' => '',
	'pconnect' => FALSE,
	'db_debug' => (ENVIRONMENT !== 'production'),
	'cache_on' => FALSE,
	'cachedir' => '',
	'char_set' => 'utf8',
	'dbcollat' => 'utf8_general_ci',
	'swap_pre' => '',
	'encrypt' => FALSE,
	'compress' => FALSE,
	'stricton' => FALSE,
	'failover' => array(),
	'save_queries' => TRUE
);

tolong dikoreksi