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CCS/LAUNCHXL-F28379D: Questions about ADC part in TMS320F28379D

Yuansheng He
Prodigy 175 points
Part Number: LAUNCHXL-F28379D

Tool/software: Code Composer Studio

Hello all,

I have some Questions in LAUNCHXL-F28379D ADC.

TMS320F38279D has two resolutions, and what is the allowable voltage range for VREFHI&VREFLO in each resolution mode in this product?

I have tested the ADCINA2 pin, and it seems that it is not working. Is there anything I've missed?

The package type of PTP inputs have not CMPIN5N, then can this channel (CMPIN5) works under 16bit mode? 

Best regards,Ditny.

  • 0
    TI__Guru 60865 points
    Hi Ditny,

    You can get the VREFHI and VREFLO ranges in each mode from the device datasheet "ADC Operating Conditions" tables: www.ti.com/.../tms320f28377d.pdf

    The launchpad also has an erratum concerning the A2 input on some versions of the board:
    e2e.ti.com/.../581950
  • 0 in reply to Devin Cottier
    Prodigy 175 points
    Thank you Devin Cottier.
    Do you know how much voltage the LAUNCHXL-F28379D supply to VREFHI&VREFLO? If the chip REF5030 in board changes to other chips, does the VREFHI change?
    Since the PTP type package doesn't have CMPIN5N, can F28379DPTPS works in 16 bit mode in CMPIN5 channel?
    Anther Question is that if the external voltage reference generation circuitry is necerssaryfor F28379D in adc mode.

    Regards, DITNY.
  • 0 in reply to Yuansheng He
    TI__Guru 60865 points

    Hi Yuansheng,

    If you replace REF5030 with REF5025 the VREFHI voltage will change from 3.0V to 2.5V.  One of these two voltages are what you would use for the ADC reference voltage for almost all applications.

    Yes, you absolutely need to supply the external reference voltage for the ADC to work (in any mode).  It needs to be buffered in any mode.  It needs to be very low noise for 16-bit mode.  What is on the launchpad should be pretty good for 16-bit mode.

    For 16-bit mode you need both input channels.  Since C5 is missing from the C4/C5 channel pair on the 176-pin PTP package you can't use this channel for 16-bit mode. 

  • 0 in reply to Devin Cottier
    Prodigy 175 points

    Hi, Devin Cottier. Thanks a lot. It is really helpful.

    But I do not understand about  ' It needs to be very low noise for 16-bit mode. '. It is said that 16bit mode can be more advantageous in case of noise in the F2837* datasheet as shown below. So can you make more detail explanantion?

    Best regards, Ditny.

  • 0 in reply to Yuansheng He
    TI__Guru 60865 points
    Hi Yuansheng,

    The ADC reference is very sensitive to noise; any noise that is on the reference input will show up directly on the output. Because of this it is very important to use a good reference circuit with low noise.

    In differential mode, the ADC inputs are reasonably tolerant of noise since common mode noise can be rejected (as the quoted section of text suggests).
  • 0 in reply to Devin Cottier
    Prodigy 175 points
    Thanks Devin Cottier!