Random Password generator in PHP

public function generateRandomPwd($num = 7)
{
$char = "023456789abcdefghijkmnopqrstuvwxyz!@#$%^&*";
srand((double)microtime()*1000000);
$i = 0;
$pass = '' ;
while ($i <= $num) {
$num = rand() % 33;
$tmp = substr($char, $num, 1);
$pass = $pass . $tmp;
$i++;
}
return $pass;
}