<?php

$str = 'A ju kaskdn kskj pstru askdol l asjndk;llll masd masdmasdoa sd as mmm.';
// simple, also need with charsLimit
function trimWords($str, $wordsLimit, $endCharacter) {
  $strPieces = explode(' ', $str);

  $neededPices = array_slice($strPieces, 0, $wordsLimit);
  $result = implode(' ', $neededPices) . $endCharacter;

  return $result;
}

var_dump(trimWords($str, 5, '...'));