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OPA2187: CMRR spec

Ryuuichi machida
Guru 11505 points
Part Number: OPA2187

Hello

Let me confirm about below.

* According to datasheet, CMRR spec of OPAx187 is described as shown below.

1. Condition : (V–) – 0.1 V < VCM < (V+) – 2 V, VS = ±18 V

Spec : Min 126dB, Typ 140 dB

2. Condition : (V–) < VCM < (V+) – 2 V, VS = ±18 V, TA = –40°C to +125°C

Spec : Min 130dB, Typ 145 dB

Are above specs swapped ?

I believe that spec of "2" condition should be worse than spec of "1" condition.

Best Regards,

  • 0
    TI__Guru 60570 points

    Ryuuichi,

    If the CMRR test conditions were the same at 25C and over -40C to 125C temperature range, you are correct in thinking that at 25C CMRR specs should be higher.

    However, since at 25C CMRR is tested at input common-mode voltage 100mV lower than in latter case, any non-linear increase in the Vos within this lowest 100mV range (change in Vos vs Vcm slope) will show as lower CMRR spec: CMRR=ΔVcm/ΔVos.

  • 0 in reply to Marek Lis
    Guru 11505 points

    Hello Lis-san,

    However, since at 25C CMRR is tested at input common-mode voltage 100mV lower than in latter case, any non-linear increase in the Vos within this lowest 100mV range (change in Vos vs Vcm slope) will show as lower CMRR spec: CMRR=ΔVcm/ΔVos.

    Understood about above.

    However, I'm not sure which case VCM become "(V-) - 0.1V".

    In general, I understand that input voltage should be within supply voltage. So, general VCM spec is defined "(V-) + xxx" to "(V+ ) - xxx".

    Could you please tell us what kind of case you assumed and defined "(V-) - 0.1V" ?

    Best Regards,

  • 0 in reply to Ryuuichi machida
    TI__Guru 60570 points

    Ryuuichi-san,

    The Input common-mode voltage range in rail-to-rail input op amps can actually go beyond the rails and in case of OPA2187 at 25 deg C it extends from 100 mV below negative rail to 2 V below positive rail irrespective of the actual supplies.

    This may be written as:  (V-) - 0.1V < Vcm <  (V+) - 2V

    Therefore, for  Vs=+/-18V  the linear input voltage range is from -18.1V to 16V while for single 5V supply Vcm range is from -0.1V to 3V.  

  • 0 in reply to Marek Lis
    TI__Genius 11135 points
    Ryuuichi-san

    We haven't heard back from you so we assume this answered your questions. If not, just post another reply.

    Thanks
    Dennis
  • 0 in reply to Dennis Goeke
    Guru 11505 points

    Hi,

    Sorry for my late reply.

    I understood your answer, and can close this therad.

    BR,