Unable to use Memcached in PHP Fat free framework

I have been trying to implement memcached in my application built in fat free framework. I have read that it should be explicitly defined as "memcached=192.168.--.---:11211" but no matter how I implement it, it uses "folder=tmp/cache/"

Tried and failed approaches

1. 
   config.ini
   CACHE="memcached=192.168.--.---:11211"
   

   index.php
   $f3->config('config/config.ini');
   $f3->run();

   code
   $cache = \Cache::instance();
   var_dump($cache);
   

   Output
   Object(Cache)#7 (3) {
   ["dsn":protected] => string(17)"folder=tmp/cache/"
   ["prefix":protected] => string(12)"randomString"
   ["ref":protected] => NULL
   }

2. 
   code
   $cache = \Cache::instance();
   $cache->load("memcached=192.168.--.---:11211");
   var_dump($cache);

   Output
   Object(Cache)#7 (3) {
   ["dsn":protected] => string(17)"folder=tmp/cache/"
   ["prefix":protected] => string(12)"randomString"
   ["ref":protected] => NULL
   }

3. 
   code
   $cache = new Cache("memcached=192.168.--.---:11211");
   var_dump($cache);
   

   Output
   Object(Cache)#7 (3) {
   ["dsn":protected] => string(17)"folder=tmp/cache/"
   ["prefix":protected] => string(12)"randomString"
   ["ref":protected] => NULL
   }

4. 
   index.php
   $f3->config('config/config.ini');
   $f3->set('CACHE',"memcached=192.168.--.---:11211");
   var_dump($f3->get('CACHE'));

   Output
   string(17)"folder=tmp/cache/"

What am I missing?

Do you have installed the proper php extension? Or is the connection secured? Because when there’s an error, the cache engine will just fall back to folder mode.