Hi Thiago Palmieri,
KL43 and KL27 already have the ROM bootloader, it supports USB,I2C,SPI and LPUART peripheral interfaces, you don't need to use the flash bootloader again.
When you use the ROM bootloader, just make sure your MCU is boot from ROM, You can check your flash address 0X40D(FTFA_FOPT), bit 7-6 indicator the boot source selection.
About the example and document, please refer to kinetis bootloader1.2.0, the link is: www.freescale.com/KBOOT
Wish it helps you!
If you still have question, please contact me!
Have a great day,
Jingjing
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