• TI Thinks Resolved

OPA551: Can I operate opamp where Vin is more than supply rails?

Part Number: OPA551

Hi,

I am using OPA551 in a unity gain configuration with supply rails at +-10VDC. My application requires a static input voltage range of 0 to 15VDC. According to the spec sheet, Vin can not exceed more than 0.5V  from supply rails.I had experimented with 0-15VDC input range in the lab setup. The op ams seems to operate with higher input range. Please advise, can I operate above rail settings? What are the drawbacks if I operate above rail settings.

Thanks,

Sumeet

  • Hi Sumeet,

    The OPA551 common-mode input range is rated from (V-)+2.5 V to (V+) -2.5 V; that is the assurred linear operating range. In actuallity, the device likely still functions and amplifies somewhat beyond the specified range. That is not an uncommon behavior for operational amplifiers. They uusually still "work" up to a point.

    What is likely to be observed is degradation of many of the electrical operating parameters. What we have observed in such cases is degraded common-mode rejection, decreased open-loop gain, increased noise and distortion, reduced bandwidth, and degradation of dc parameters. This worsens as the range is further exceeded and at some point the output usually locks up against an output rail.

    You can certainly push the limits and operate the OPA551 in this manner, but TI can make no assurances about any peformances when the datasheet conditions are exceeded.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • In reply to Thomas Kuehl:

    Thanks Thomas for the reply! Once IC is locked up, does it unlocks itself after power is removed or this is an indication of permanent IC damage?
  • In reply to Sumeet Sharma:

    Hi Summet,

    The behavior hasn't been characterized because we don't characterize devices outside their specified operating region. However, I do expect that the OPA551 won't be damaged and will resume normal operation once it is back operating within its linear input and output ranges.

    Regards, Thomas

    Precision Amplifiers Applications Engineering