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I was wondering about the common-mode input range of the OPA837 when used as a reference buffer for an ADC.
The TIDA-01055 compares the OPA625 with the OPA837 as a lower power option. In Figure 7 of the Design Guide V1 = 4.1V (similar to Figure 10). But 4.1V at the non-inverting input of the OPA837 violates the common mode input range when powered from a 5V supply. OPA837 datasheet states 3.8V typ. for its high input CM voltage.
1) Why is the OPA837 suggested for this application? (I am considering the OPA837 for a similar application.)
2) What is the meaning of "< 3-dB degradation in CMRR limit" on page 8 of the datasheet concerning the input CM?
[1] https://www.ti.com/tool/TIDA-01055
[2] https://www.ti.com/lit/ds/symlink/opa837.pdf
Thank you for the quick response.
Yes, I have read this section. But this solely describes linear behaviour.
What happens if V_ICR is violated? Does only CMRR degrade? How much does it degrade? I guess this is application specific and must be tested there? Are there further side effects I am not aware of?
Hi Martin,
it stops working properly...
By the way, the common mode input voltage range isn't violated, because the OPA837 is used in a composite amplifier:
Kai
Yes Martin, this was a long internal argument - if you target a certain output voltage in this composite, the input voltage for the output stage set for gain of 1.5 is 2/3 of that, in range.