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AM2434: USB-DFU Boot Mode Power Supply Restriction 3.3V

Mari Tsunoda
Expert 3850 points
Part Number: AM2434

Tool/software:

Hi Team

My customer has a question about USB boot mode. 

It says in the schematic review checklist that: 

6.1.5.2.1 Notes for USB Boot Mode
USB0 interface supports boot. When the USB0 is configured for DFU boot mode, 3.3 V supply (permanent or
switched) is not recommended to be connected to the USB0_VBUS pin. No permanent supply (equivalent to the
divider value) is allowed to be connected to the USB0_VBUS.

What is the reason that a 3.3V supply is not recommended?

Best regards,

Mari Tsunoda

  • 0
    TI__Guru**** 151189 points

    Hello Mari Tsunoda

    Thank you for the query.

    The USB0..1 interface needs a voltage divider to be connected to the input VBUS voltage and the divided output connects to the SOC USBx_VBUS.

    Refer below 

    9.2.4 USB VBUS Design Guidelines

    The divider is a requirement that comes from the IP and we recommend customers to follow these recommendations. 

    Customers tend to connect 3.3V directly to the USBx_VBUS based on previous design use case familiarity and this note is to caution customers from connecting the 3.3V supply directly to the USBx_VBUS assuming the input is in the allowed range. 

    Note that the USBx_VBUS is a fail-safe pin only when the USB VBUS design guidelines are followed.

    Regards,

    Sreenivasa