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Thread: Rigid-Flex Custom Teensy 3.2 not loading the firmware

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  1. #1
    Junior Member
    Join Date
    Feb 2017

    Rigid-Flex Custom Teensy 3.2 not loading the firmware

    Dear PJRC Community,

    We have a prototype project that require a rigid flex PCB design. It implies a custom Teensy 3.2 board. We have already some experience with rigid Custom Teensy 3.2 with success in two previous projects.

    Our first units are not loading the firmware, we have been investigating about the problem, and particularly have been checking the different ideas found on:

    Items we have checked:
    • VBAT is connected with the external 3.3V supply.
    • VREGOUT is connected with the 3.3V supply trough a BAT54C diode.
    • Pin 33 PTA4 is floating
    • D+ and D- are not swapped
    • Differential Pair was certified and measured by PCB manufacturer at 85 ohms.
    • PROGRAM signal when the pushbutton is not pressed is at: 3.289V
    • RESET signal while holding the pushbutton down is: 0.002V

    I have measured the signal on MK20 RESETB using the oscilloscope:

    Click image for larger version. 

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    Click image for larger version. 

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    Here I attach the schematics and layouts of the project, please check the attached file "STX_Rigid_Flex_Design.pdf". While the PCB Stack is rigid-flex, the Teensy 3.2 components are all located in a rigid part, the flexible parts are only used for buses.

    Can you please give an advice or idea on things we might also review? In the meanwhile we will continue looking for the issue and double-checking everything.

    Attached Files Attached Files
    Last edited by ElkinDiaz; 07-28-2020 at 11:24 AM.

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