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LAUNCHXL-F28379D: VDAC/VREFHI of the buffered DAC

Jingtai
Genius 4575 points
Part Number: LAUNCHXL-F28379D

Launchpad support,

In order to output from the buffered DAC the VDAC/VREFHI are required to connect to an external reference voltage but I am not able to figure out the pin in from J1-J8 on the Lanuchxl-F28739D except U11 and U19 which are difficult to wire. Where is an external reference voltage connected to VDAC/VREFHI?

Best regards,

Jingtai

  • 0
    Expert 2520 points

    Hi,

    Launchpad schematic is available in your Launchpad User's Guide:

    Looks like VDAC (ADCINB0) pin is not wired anywhere. VREFHI pin depending on which DAC you are using is either VREFHIA or VREFHIB. Please look into Analog Subsytem chapter,  Analog Subsystem Block Diagram figures in TRM:

    In addition to VDAC, DACOUTA and DACOUTB DAC's can be referenced to VREFHIA. DACOUTC is can be referenced to VDAC or to VREFHIB.

    Edward

  • 0 in reply to EK
    TI__Intellectual 1360 points

    Due to holidays, you can expect a response by first week of January.

  • 0 in reply to EK
    TI__Mastermind 40935 points

    Thanks Edward.

    Jingtai,

    He's referring to the figure below to see the VREFHI to DAC hook-ups.

    Best,

    Kevin

  • 0 in reply to Kevin Allen18
    Genius 4575 points

    Kevin,

    Thanks for your reply.

    I have gotten a clue from SPRUI77C.

    Revision 1.1:

    • ADCINA2 is shorted to VREFHIB. It is recommended that users avoid using the ADCINA2 channel.

    Is it correct?

    If it works an external reference voltage is able to supply to VREFHIB via J3-29.

    Best regards,

    Jingtai

  • 0 in reply to EK
    Genius 4575 points

    Edward,

    Thanks for your reply.

    I have gotten a clue from SPRUI77C.

    Revision 1.1:

    • ADCINA2 is shorted to VREFHIB. It is recommended that users avoid using the ADCINA2 channel.

    Is it correct?

    If it works an external reference voltage is able to supply to VREFHIB via J3-29.

    Best regards,

    Jingtai

  • 0 in reply to Jingtai
    Expert 2520 points

    Jingtai,

    What you see in SPRUI77C I think is a defect of Rev1.1 PCB, which made ADCINA2 accidentally shorted to VREFHIB. I don't think you can just feed Lanchpad with your own Vref to J3.29, I think VREFHIB is still driven by U11 as shown on schematics. So you would need to desolder U11 first or cut the trace.

    Edward

  • 0 in reply to EK
    Genius 4575 points

    Edward,

    Thanks for your reply. You are right. I have measured and nowadays ADCINA2 is not shorted to VREFHIB. It seems that there are no any pin ins  to the VREFHIA/VREFHIB/VCAD on Launchxl-F28379D.

    Best regards,

    Jingtai