Hello @emb02,
As you point out, the actual size of the on-chip Flash is 512KB. This is mentioned in LPC546xx Product data sheet. Section 7.8. On-chip flash: "The LPC546xx supports up to 512 kB of on-chip flash memory."
We will let the team in charge to know about LPC546xx Product data sheet. Fig. 4. LPC546xx Block diagram for upcoming updates.
Is LPC546 Internal Flash sharing memory with EEPROM or it is having separate memory allocation?
Could you please take a look to LPC546xx Product data sheet. Section 7.11. Memory mapping. Fig 9. LPC546xx Memory mapping? There you might find their memory allocation.
Best regards, Raul.