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# OPA4277-SP: OPA4277-SP Vos

Part Number: OPA4277-SP

In the OPA4277-SP datasheet there are multiple entrees for Vos.

Is the first entry (Spec=Max +/-65uV) at 25C and post rad?  To add temperature would I add Vos(Temp_Drift)=0.15uV/C x (Hot_Temp - 25C)?

Vos(Max)=+/-65uV +/- 0.15uV/C x (Hot_Temp -25C)

What is the 2nd Vos(Max)=+/-140uV in the table?  Is this for -55C to 125C and no radiation?   It does not seem to matchup with the 1st entry and the Vos(Temp_drift) of 0.15uV/C over that temp range.  The temp_drift slope is quit a bit larger than 0.15uV/C to satisfy the Vos of +/-140uV.   If I used this entry would I need to scale it to my temp range and also add radiation variation from the TID report?

Thanks,  Brian

• Brian,

The first spec with max Vos of +/-65uV applies to pre and post-irradiation being applied.

To obtain the typical value of Vos at 125C range, you need to do following: +/-20uV+/-0.15uV*(125C-25C) = +/-35uV where 0.15uV/C is equal to a one standard deviation (sigma).

To obtain the maximum value of Vos at 125C range, you would do the following: +/-65uV+/-0.75uV*(125C-25C) = +/-140uV where max drift = 5*sigma or 0.75uV/C (see below).

The second entry applies only to pre-irradiated (no radiation) case and thus you would need to add the radiation effect from TID report.

• Marak,

This calculation sees to be off:

To obtain the maximum value of Vos at 125C range, you would do the following: +/-20uV+/-0.75uV*(125C-25C) = +/-140uV where max drift=5*sigma or 0.75uV/C (se below).

Wouldn't it equal = +/-20uV +/-0.75uV * (125C -25C) = +/-95uV?

To equal +/-140uV the max drift would need to increase to (140uV - 20uV)/(125C-25C)= 1.2uV/C?

Thanks,  Brian

• Hi Brian,

For the maximum Vos value over temperature range you must use maximum Vos at 25C (means +/-65uV and not +/-20uV - it was a typo) and the maximum drift value of 0.75uV/C (5-sigma).  Therefore, max Vos @125C = +/-65uV+/-0.75uV*(125C-25C) = +/-65uV+/-75uV= +/-140uV where 5-sigma specs limits are usually used to specified max/min limits when parts are not tested over temperature in production.  For this reason such derived limit is not an absolute guaranteed of the spec but nevertheless assures that only 1 out of 1.744 million units may be outside of said limit (see below).

• Marek,

Does that mean the +/-140uV not only includes temp but also post-rad variation?  I looked through the TID report for this device and the Vos spec used for post-rad (25C) was < +/-65uV.  The Vos data indicated that all devices post-rad fell below this threshold.

Thanks,  Brian

• Brian,

I'm not an expert on the effects of the irradiation on particular spec like Vos but I would think that there is a reason why the drift specification is given only as pre-irradiated. Thus, even though the Vos at 25C is specified under pre-and post-irradiated test conditions, once you change the temperature from 25 deg C your calculated max Vos using pre-irradiated drift spec it's not valid for post-irradiated conditions.