Transact SQL :: CASE - Maximum Number Of WHEN / THEN Conditions

I need to update many rows in some table.  I've made such SQL query:

UPDATE [%TableName%]
SET [%FieldName%] = CASE
            WHEN ID = 1 THEN '1'
            WHEN ID =2 THEN '2'
            ....
       END;
       [%FieldName2%] = CASE
            WHEN ID = 1 THEN '1'
            WHEN ID = 2 THEN '2'
            ....
       END;
WHERE ID IN {1, 2, ...}

Are there some limitations for CASE operator? How many "when - then" conditions can I include in query?