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ADA4096 not clamping input in unity gain buffer test circuit

I'm testing the ADA4096-2 amplifier. The testing circuit is an unity gain buffer with a 30Hz sine signal, with dual +/- 3V supply, both amplifiers receive the same signal. I see the output is clamped correctly to the supply voltage values, however, as I increase the amplitude of the signal (>4V above the positive rail), the positive clamping starts to fail and the voltage in the positive power supply rail starts to raise. I'm attaching the image of the test circuit and the signals we are seeing (the red trace is the source signal, the yellow one is the amplifier output).

Am I doing anything wrong? I expected the clamping to work up to 32 V above and below the power rails and not to affect the power rails at all.

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  • The output starts to raise along with the power supply positive rail. Your explanation makes lot of sense. The power supply is a LDO incapable of sinking current and the test circuit has no other load, so when the input voltage increases too much the current is shunted to the positive rail, increasing its voltage, as the power supply of the amplifier increases then, so does the clamping level. I missed the D1 to D4 diodes in the ADA4096 internal schematic.

    Thanks a lot.

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  • The output starts to raise along with the power supply positive rail. Your explanation makes lot of sense. The power supply is a LDO incapable of sinking current and the test circuit has no other load, so when the input voltage increases too much the current is shunted to the positive rail, increasing its voltage, as the power supply of the amplifier increases then, so does the clamping level. I missed the D1 to D4 diodes in the ADA4096 internal schematic.

    Thanks a lot.

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