Other Parts Discussed in Thread: OPA2340
Hello Team,
Pepperl+Fuchs has decided to use the OPA2340 in a PLC application. For max Offset drift calculation over temperature (-40-85C), they need to know the max value.
In the datasheet I have found the following information but shouldn't this be 120uV/C and not 120uV/V. Is this a mistake in the datasheet?
Typical value at 25C is 2.5uV/C.
It would be great to get a feedback.
Best wishes
Manuel Infante
Senior Field Application Engineer
Analog
______________________________________________________________________________________________________________________________
From: Hidalgo, Sergio
Sent: Thursday, July 05, 2012 8:51 AM
To: Infante-Bernal, Jose-Manuel; Kumar, Vaibhav
Cc: precisionanalogsupporttucson@list.ti.com - PA Support Tucson Employee List (May contain non-TIers); precisionamps@list.ti.com - Help for Precision Amplifier Products (PA-Linear) (May contain non-TIers)
Subject: RE: OPA2340 temperature offste drift max -40/85C / Pepperls+Fuchs/ PLC System
Manuel,
That is the PSRR over temperature limit of 120uV/V and not offset drift. For offset drift typical spec is 2.5uV/C and there is no max value specified.
Manuel,
Since there is no over temperature production testing of OPA2340, there can be no absolute guarantee of the maximum input voltage offset drift. However, one may use statistical analysis to determine a relative guarantee, which requires accepting certain fallout rate.
The OPA2340 offset voltage drift histogram below depicts an absolute value of the offset drift and not an actual Gaussian distribution which would show positive and negative drift values, however, it may still be used to determine a value of a standard deviation (sigma). Knowing that the +/-1-sigma represents 68% of the entire distribution (see below Normal Gaussian Distribution chart), one may look at the PDS drift shown below and determine that sigma comes out to be around 4uV/C where total accumulation of units adds up to 68%.
Knowing that the sigma is around 4uV/C, customer may assume the OPA2340 maximum offset drift to be:
- 12uV/C (3*sigma) where 1 out of 370 units will NOT meet this max spec
- 16uV/C (4*sigma) where 1 out of 15,787 units will NOT meet this max spec
- 20uV/C (5*sigma) where 1 out of 1,774,277 units will NOT meet this max spec
- 24uV/C (6*sigma) where 1 out of 506,797,345 units will NOT meet this max spec
etc.
Therefore, depending what failure rate Pepperl+Fuchs is willing to accept, they should use appropriate maximum drift spec from the list above.
