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How to test the spec Long Term Stability in the Datasheet?

Harson
Expert 3700 points

Dear all,

A customer asks a question about the Spec of Long Term Stability.

He is curious about the detail or method of testing this spec:

As our Datasheet descriped:

 Long term stability refers to the change of the output voltage
of a reference over a period of months or years. This effect
lessens as time progresses as is apparent by the long term
stability  curves.  The  typical  drift  value  for  the  REF30xx  is
24ppm  from  0-1000  hours,  and  15ppm  from  1000-2000
hours.  This  parameter  is  characterized  by  measuring  30
units at regular intervals for a period of 2000 hours.

I know what's the meaning of this spec but I'm not sure about the test process of this spec and how to caculate by 30 units. By average or other method?

As seen from the figure on page 7, its average value does't seen to be 24ppm. 

  • 0
    TI__Guru 64530 points

    REF30xx long-term stability spec is based on measuring the shift in VREF output voltage over a given period of time and expressed in PPM.  The units are kept at constant room temperature during the test and the shift is calculated as the change between initial (0 ppm) and the final readings (two-point shift).  The typical spec for 0-1000hrs is an average shift in all the units used in the test and looking at the graph (below) it does look to be 24ppm at 1000hrs point (see red line) thus I am not sure I understand your question.


  • 0 in reply to Marek Lis
    TI__Expert 3700 points

    Dear Mark,

    Thank you for you great answer, I know the test method of LTS, and what i said "it does look to be 24ppm at 1000hrs"  means:

    Seen from the picture you posted, I'm afraid the average value is not 24ppm, because most of the value was below 20ppm.

    But now I think maybe  24ppm is the maximum average value of the LST.      

     

    I have another problem is :                  As I read some articles:  the LTS is decreasing in expoential as hours increased.

    So I can understood why the LST of 1000-2000 Hours is smaller than 0-1000 hours, but looking from the red line in the picture you posted I confused, so may be I got wrong information from the articales.