The most obvious case regarding this has been California's Prop 8 which revealed a large push of donor money fueled anti-gay sentiment in the largest state of the union. The Mormon Church was largely to blame, which led to a lawsuit to overturn Prop 8 in the court system. At issue--do civil rights of a class of people negate the will of the referendum? In this case, both constitutional rights are in conflict which means the court system should decide the matter unless a different referendum is voted upon that obviates the controversy.
Courts have the job to administer the law. Both "ordinary" and constitutional law. A constitutional court can decide on matters of constitutional law. This function can be exercised for both representative (indirect) and direct democracy. Thus if an "ordinary" law has been passed by referendum then the courts may be asked to decide if the law, for instance, introducing a minimum wage or abolishing corporal punishment, accords with the constitution or not. If the constitution is amended by correct democratic process (direct or indirect democracy) then the (constitutional) court may not block such a reform but must administer the new law.
Dr. M. For
No matter what is written in constitutional law, non-elected judges should never have the power to declare a law invalid by reason of it being unconstitutional. This is because judges are not elected therefore the process is undemocratic. There is nothing in the constitution that should be considered more or equally important to the decisions of voters and their leaders. Direct democracy is not significantly different from representative democracy in this argument. Tyranny of the majority is preferable to "judicial review"