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ADS1278-EP: Start-up sequence help

Christopher Ramirez
Prodigy 30 points

Part Number: ADS1278-EP

I am jumping in on an existing design using this part and was looking at the start up sequence on page 35 of the datasheet. Figure 81 shows a staggered power up for AVDD, IOVDD, and DVDD. My question is how do I do this? Do I need to add in some resistors to change the time constant for the 10uF and 0.1uF bypass caps? is there an example circuit I can see doing this?

I have looked at evaluation boards and well as other examples and none show me how this is done.

All I see are the bypass caps at the VDD inputs.

Thanks

  • 0
    TI__Guru 51400 points

    Hello,

    The Start-up sequence is required to ensure the internal power-on reset circuit works correctly.  If you do not meet this requirement, the part will still function  correctly if you assert the /SYNC pin after the supplies have ramped up to within recommended voltage ranges and after data first appear, indicated by /DRDY transitioning from high to low.

    The evaluation board does not always meet this power-up sequence, and pulses the /SYNC pin to ensure proper operation.

    If you want to meet these requirements, most LDO's have an enable pin that can be controlled by a power-up sequence IC or simply use RC's to set different time delays, meeting the staggered power-up sequence.  

    Most designs do not meet the start-up sequence requirements and simply rely on assertion of /SYNC  pin for proper operation.

    Regards,
    Keith Nicholas
    Precision ADC Applications