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AD8599 CMRR measurement and mistakes on datasheet ?

Question asked by A.Roseng on Oct 20, 2012
Latest reply on Jan 17, 2013 by NeilJ

Hello my friends,

 

I have to use an AD8599 and I tried to measure the CMRR with Vcc=+/-5V with -2V<Vcm<2V (as noted in the datasheet). The result is about 110bB (vs 120dB Min). I tried using conditions Vcc=+/-15V with -12.5V<Vcm<12.5V and it's the same. I carry out these measurements with DC conditions.

Could you help me if you know conditions to reach the value given in the datasheet?

 

I tried 2 bias methods:

In accordance with MIL-STD: Vcc+=+7V; Vcc-=-3V; Vin=+2V and Vcc+=+3V; Vcc-=-7V; Vin=-2V

with a direct method (instrumentation amplifier between In+ and In-): Vcc+=5V; Vcc-=-5V; Vin=-2V then Vin=+2V

The Delta of the Vio is about 10µV with -2V<Vcm<2V.

Then, I downloaded the Pscipe model on the AD website... I've got the same results!

 

I have another comment, I think there is a mistake on the datasheet Rev. C (page 3): the condition of the Open Loop Gain with Vsy=+/-5V specifies -11V<Vo<11V... Wahoo... Beyond the rail!!!

 

Thank you for your answers.

Alex.

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