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ADS124S06: IOVDD connected to AVDD

PLCmatic
Prodigy 90 points
Part Number: ADS124S06
Other Parts Discussed in Thread: DAC8311, SN74LVC2T45

Hi All,

I am using an ADS124S06 togheter with a DAC8311 . DVDD of ADS124S06 supply is connected to a +3.3V supply.

A low noise +5V analog supply is available on the board and it is connected to AVDD and REP0 of ADS124S06 and to AVDD of DAC8311.

Both devices share same SPI bus.

I would connect the +5V low noise supply to IOVDD in order to use the SPI bus at 5V: could it be a problem in terms of noise coupled into AVDD and REFP0?

Thank you for your support

Best regards

  • 0
    TI__Guru** 112725 points
    Hi PLCmatic,

    Welcome to the E2E forum! There is always the possibility for noise, but as you are already powering the DAC8311 with this source it shouldn't be any worse using the same supply for IOVDD. This concept should work if the supplies are properly bypassed (decoupled) and good PCB layout practices are used to keep digital signals from crossing analog domains. This becomes a little tricky with return current paths, so a good ground plane is essential. You could also add some additional larger capacitance values in parallel with the 100nF bypass caps on the ADS124S06 analog supplies as a current reservoir of charge.

    Also note the Power-Supply Sequencing section 11.2 on page 98 of the ADS124S06 datasheet. An additional Reset may be required.

    Another option would be to use 3.3V for IOVDD and a level translator to the DAC such as the SN74LVC2T45. As I don't know anything about your system this may or may not be practical.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Prodigy 90 points
    Hi Bob,

    thanks for your answer and hints!
    Unfortunately we cannot allow SN74LVC2T45 due to strictly space contraints.
    Anyway the low noise 5V supply do not feed directly the analog chain (an op amp, DAC and ADC) but it is first filtered with a pi filter.

    Low noise 5 V --> Pi filter --> Analog chain supply (dedicated pcb copper area)

    This is because 5V rail supplies other few components like digital isolators and open collector comparator so we choose to feed all the analog pins through a dedicated filter.

    Every analog IC power pins is decoupled with at least a 1uF MLCC cap in parallel with 10 nF MLCC cap towards ground plane.

    Hopefully this should be enough!

    Best regards and thanks again
    PLCmatic