I'm making a simple UHF transmitter with MICRF102 (Micrel IC). It's working ok, but the modulation need to be ASK.
Does anyone know any other IC with the same function but need to accept FSK modulation?
Have you looked up the definition of ASK? It should become very clear how to do ASK. In fact, the first page of the MICRF102 datasheet gives you a huge hint - it's also called OOK (on-off keying).