Hi
I am afraid we don't have secondary bootloader for LPC546xx.
LPC546xx has on chip USB bootloader. for detail, see
Chapter 3: LPC546xx Boot process
This is the list of boot source:
Have a nice day
Jun Zhang
Hi 寶凱 李
We don't have exact USB CDC secondary bootloader demo code.
But you can refer SDK USB CDC demo code to develop your secondary bootloader CDC driver .
usb cdc demo is included in MCUXpresso SDK package.
Welcome | MCUXpresso SDK Builder
Have a nice day,
Jun Zhang