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OPA191: Input Protection Clamps impact on offset and bias current

Mitchell
Expert 4915 points
Part Number: OPA191
Other Parts Discussed in Thread: OPA192

Hi Team,

If we were to engage the input protection clamps on the OPA191/192 would this cause any change in the DC offset or bias current performance?

Thanks,
Mitchell

  • 0
    TI__Guru* 93105 points

    Hi Mitchell,

    The CMOS OPA191/OPA192 has ESD protection diodes connected from each input to each supply rail (see OPA192 datasheet Figure 65). These are very low-leakage current diodes that are turned off when the OPA191/OPA192 is operated within its specified linear input voltage range. The common-mode voltage range, VCM is from (V–) – 0.1 to (V+) + 0.1 V. When that range is observed the ESD protection diodes stay off and only exhibit minute leakage currents that mostly define the input bias current of these op amps.

    If you engage any of these input ESD protection diodes I expect what you mean is you are applying an input voltage that exceeds that of the specified input range, and one or more of the diodes are conducting more current than just leakage current. The diode in that case would have to be forward biased by the input voltage and the op amp input voltage is no within the linear operating range. Once that happens the input voltage offset and input bias current will increase. The input op amps inputs because of the ESD diodes can handle an input current up to +/-10 mA without damage. That shouldn't cause any shifts in the voltage offset and input bias currents. Once the current is reduced normal operating levels should be reestablished.

    Regards, Thomas

    Precision Amplifiers Applications Engineering