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ADS1120: POR

richard fenton
Prodigy 30 points
Part Number: ADS1120

We have a number of prototype boards that use the ADS1120. These were designed before we were aware of the DVDD supply ramp requirement and have a supply ramp that is much faster than the specification. These boards have been tested at +71°C and powered up correctly. It will be very useful if these continue to work. Do you know if ADS1120 POR will continue to work correctly at 71°C or will it degrade over time and stop working?

  • 0
    TI__Guru** 113765 points

    Hi Richard,

    The issue worsens with increased temperature.  Most likely if it works it will stay working.  Temperature and wafer process variation are the two known variables that affect the POR.  Do you have an oscilloscope shot you can send me showing your ramp?

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 30 points

    Hi Bob

    The ramp for voltage is:

    regards

    Richard F

  • 0 in reply to richard fenton
    TI__Guru** 113765 points

    Hi Richard,

    I should have been a little more specific in my request.  Was this scope plot taken at the DVDD pin of the ADS1120?  The biggest area of concern is the time from 0V to about 1.6V.  It appears by what I see with respect to simulation data you should be ok at room temperature.  As I stated earlier, the problem does get worse with increased temperature.  Unfortunately I do not have simulation results for the maximum temperature you expect, but based on the scope shot you may be at some risk.  The device should not degrade over time, but other components are likely to degrade such as capacitors as they age.

    If the scope shot is not at the ADS1120 pin, then I would look at the ramp at the DVDD pin.  Sometimes you can change the bypass cap at the supply pin to a higher value to slow the ramp and still get good bypassing (decoupling) because of the low ESR/ESL of the ceramic cap.  You could try a 1uF cap and see if this helps stretch out the early portion of the ramp.

    Best regards,

    Bob B