SQL & PL/SQL

I want to put case statement in an update statement using Oracle 10g

I'm getting a syntax error on the last line Ora-00933: SQL command not properly ended

Help please

UPDATE EMP a
SET EMP.TYPE = CASE
WHEN 'Y' = 'A' THEN 'DIV'
WHEN 'Y' = '1' THEN 'DEF'
END CASE;