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TMS320F28P550SJ: 3.3V considerations when binging out J102 of LAUNCHXL-F28P55X

Wayne Huang
Genius 16665 points
Part Number: TMS320F28P550SJ


Tool/software:

Hi champs

I am asking this for our customer. 
The users wants to bring out J102 connector for XDS110 of F28P550x launchpad to the target board. 
Except TMS/TCK/TDO/TDI/GND, the user is confused if 3.3 V is needed in the cases below.
1. If the user already supply 3.3V from the target board, is it still needed to connect 3.3V from J102 to the target board?

2. if 1. is NOT. What if the user already connects 3.3V from J102 to the 3.3V of the target board, which has 3.3V supply?
3. if the user isolates 3.3V/5V JP1, is it required to connect 3.3V from the target board to supply XDS110?

That is, 3.3V of XDS110 is from the target board rather than from the USB.

  • 0
    TI__Genius 13035 points

    Hello,

    Please give me another day to look over the thread, apologies for the delay.

    Best,

    Matt

  • 0 in reply to Matt Kukucka
    TI__Genius 13035 points

    Hi Wayne,

    Wayne Huang said:
    1. If the user already supply 3.3V from the target board, is it still needed to connect 3.3V from J102 to the target board?

    It would not be necessary unless the USB delivered power is isolated.

    Wayne Huang said:
    2. if 1. is NOT. What if the user already connects 3.3V from J102 to the 3.3V of the target board, which has 3.3V supply?

    You'll have contention on the 3.3V rail which is not ideal. It should be fine functionally, but there may be unexpected XDS behavior. 

    Wayne Huang said:
    3. if the user isolates 3.3V/5V JP1, is it required to connect 3.3V from the target board to supply XDS110?

    Yes. If they wish to isolate the USB, they'd have to disconnect JP1/J101 and then power the onboard XDS power plane via J102 (+3V3_XDS110) from 3V3 of the target board. The USB would be  on the cold side and the XDS would remain on the hot side (same side as MCU) unless the target board also isolates the JTAG signals.

    Best,

    Matt