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ADS8405: ADS8405 Power Sequencing and decoupling

Christophe Niclaes49
Prodigy 130 points
Part Number: ADS8405

1. Is there any requirements for the power sequencing of ADS8405 since there are two power supplies (VA and VDB) ? I can't find any information about that in the datasheet.

2. Can I place capacitors on REFOUT pin even if I use an external Vref connected to REFIN or should I remove them (dual-version board with options)?

  • 0
    TI__Intellectual 2540 points
    Hello Christophe,


    1. I have reached out to the design team in order to better understand if the power sequencing of VA and VBD needs to match a specific sequence. I will follow up with you once I received an answer.

    2. Page 18 of the datasheet for the ADS8405 shows the typical setup for using an external reference (Figure 31) or using an internal reference (Figure 32). In both options the reference capacitors should be installed and should be very close to the ADC in the layout.


    Thank you,
    Reed Kaczmarek
  • 0
    TI__Mastermind 24940 points

    Hello Christophe
     
    There is no need to place capacitors on REFOUT if using an external reference, REFOUT can be left unconnected. If you would like, you can place an unpopulated 0ohm resisitor between pin REFOUT and REFIN to have the option available to use the internal reference. You will also need to disconnect the external reference device if using the internal reference. 
     
     
    Regards
    Cynthia

  • 0 in reply to Cynthia
    TI__Intellectual 2540 points
    Hello Christophe,

    I have heard back from our design team about the power sequencing and you should ensure that VA comes on before VBD. This will keep you within the absolute maximum rating for +VA to +VBD being -0.3V to 2.55V (as seen on page 2 of the datasheet).

    Thank you,
    Reed Kaczmarek