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OPA659: Vout stuck at 1V when input grounded

Part Number: OPA659

Hello,

I have built  simple voltage follower using this opamp with single VCC 10V to gnd ( +Vs=10V , -Vs=0V)

If I short noninverting input to gnd directly or through 50R, the output goes to 1.14V. If I drive the noninverting input with square wave it must be offset above 1.14V otherwiese it is clipped, it almost looks like common mode range is -Vs-1.14V buit in the data sheet it says common mode rangte is +-3.5V typical . Also data sheet suggest sinlgle supply operation in chapter 8.3.2. Am I missing something , are you able to help ?

Thanks Sebastian

  • Hi Sebastian,

    You are correct that you are running into some kind of headroom limitation. The spec in the datasheet that you highlight along with the output swing is relative to a specific supply configuration, in this case +-6V. For example, the output swing is +-4.8V with +-6V supplies. This means that the output will start to clip around 1.2V from the rail on each side. This can be applied to a 0V to +10V configuration, where it will start to clip around 1.2V from each rail. Meaning the output swing will be from 1.2V to 8.8V. We also have a TI Precision labs video series highlighting this idea. It can be found in the "Input and output limitations (4)" section.

    Precision labs series: Op amps | TI.com

  • Thanks Ignacio, another pair of eyes and all is clear- I have missed this thanks.