Hi,
I figured out to do this with the category id
in category.php template I wrote:
<?php $category_id = get_cat_ID(single_cat_title( '', false ));?>
in order to get the current category.
later on, the shortcode I used is:
<?php echo do_shortcode('[utcw post_term='.$category_id.' color=random title="TAG CLOUD" before_title="<h3>" after_title="</h3>"]'); ?>
the trick was to use post_term and the category id ??