548 A RANDOMIZED, DOUBLE-BLIND, DOUBLE-DUMMY, PARALLEL GROUP, ACTIVE CONTROLLED MULTI-CENTER CLINICAL TRIAL TO EVALUATE THE ADDITIONAL EFFICACY AND SAFETY OF OLMESARTAN MEDOXOMIL/AMLODIPINE 20/5 MG IN CHINESE PATIENTS WITH MILD OR MODERATE ESSENTIAL HYPERTENSION WHO FAILED TO ACHIEVE THEIR GOAL WITH AMLODIPINE 5MG MONOTHERAPY