5 Replies Latest reply on Jun 10, 2020 9:40 AM by SananyaM_56

    FX2LP18 hardware PCB recommandation



      The FX2LP18 is definitiely choosen for our board.

      I read the AN15456 application note to write my specifications.


      Is there any others recommandation for FX2LP18 with 1.8 VIO ?

      Concerning the 1.8V LDO which one is recommanded ?

      Is there any schematics to be shared ?



        • 1. Re: FX2LP18 hardware PCB recommandation



          Please refer to the schematics from the FX2LP18 DVK. Most of the hardware guidelines can be followed from AN15456 for FX2LP18 as well.


          Best Regards,


          1 of 1 people found this helpful
          • 2. Re: FX2LP18 hardware PCB recommandation

            OK. I used it.


            Concerning I2C, i see that the FX2LP18 board uses 3.3V Pull-up.


            I would prefer use VCCIO (1.8V) pullup to use a ST 1.8C I2C EEPROM. Is it possible ?


            Is the M24256 compatible with the FX2LP18 ?

            This is a 2 bytes adressable EEPROM due to its size.


            Furthermore we want to use 2 EEPROM.

            Which I2C address the FX2LP18 will search first ? 0xA0 ?



            • 3. Re: FX2LP18 hardware PCB recommandation



              Yes, you could pull up to 1.8V as well since your EEPROM supports a supply of 1.8V. However, please ensure the pull up values are adjusted to meet the VIL specification when the lines are pulled low

              The M24256 is compatible as a large EEPROM for FX2LP since it is two-byte addressable and has a capacity of 256KB.

              No, FX2LP18 will not search for 0xA0 during bootup since it does not support 0xC0 EEPROM load. Please refer to the KBA for the differences.


              Best Regards,


              • 4. Re: FX2LP18 hardware PCB recommandation



                OK thanks.


                But Something is not clear enought for me.


                I know that FX2LP18 need 0xC2 boot.

                What is not clear, is WHy you say FX2LP18 does not search for 0xA0 adress EEPROM (small one) ?


                For me a 0xC2 loading is not necessary linked to the size of EEPROM. Where it is written ?

                A small EEPROM can be 256 bytes, rigth ? (2kbits). So large enought for a 0xC2 loading for a FX2LP18 in case we only do what is proposed : reset the DISCON bit and set the RENUM bit.


                Concerning I2C :

                I see in the FX2LP18 schematics that I2C pull-up is set to FIXED 3.3V even if VCCIO can be 1.8V.

                Do you confirm it is possible ? (Different POWER for I2C I/Os and Others I/Os)

                • 5. Re: FX2LP18 hardware PCB recommandation



                  The 0xC2 boot is going to search for an EEPROM with the address of 0xA2 since the bootloader is programmed to link the EEPROM size with a pre-defined address. This is because the EEPROM size defines its addressing method so in 0xC2 boot, it will not search for a small EEPROM which is single-byte addressable and will expect the complete firmware to be present in the EEPROM to enumerate with after the disconnect. Please refer to the KBA for more details- FX2LP Failed EEPROM Boot - KBA225241


                  On the board, VCCIO can be changed to 1.8V, so pull up resistors of 10K were added which will ensure SDA is pulled low enough when operating with 3.3V EEPROM. Since you will be connecting to a 1.8V EEPROM with VCCIO as 1.8V as well, you could connect a stronger pull up such as 2.2K resistor.


                  Best Regards,