ADA4350 outputs a small DC voltage.

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Hello,

Recently designed PCB has a ADA4350 that is connected to a AD4000. Noticed 75mVDC output at pin3 (VOUT1) once the TIA is enabled - pin 16 pulled high. From  the attached schematic, C43 and R22 are removed and R21 is replaced with a solder blob to have an ideal 0-ohm connection to ground (pin 11 is grounded). The feedback paths are normally open according to figure 55 of datasheet. It must be the first stage amplifier that is causing these error voltages, or is it?

Also probed pin 12 after removing R27 and found those 75mV popped up as soon as EN goes high.

Need your expert opinion on how to remove of significantly reduce these DC voltage.

Thanks,

If the attached jpeg is difficult to read let me know and I will try to send a different link of a bigger and better jpeg.



Updated the jpeg file link.
[edited by: Mohi at 11:14 AM (GMT -4) on 18 Jun 2021]
  • It was an error on my part. I had to lift pin 14 to connect a -5V there, but the connection was faulty.

    With a confirmed -5V at pin 14, the output does reach 0V.

    A question about the output swing that is mentioned in table 6 - the output should swing to 4.87V; however, in LTSpice simulation and my experience with the new PCB, the output never crosses 4V.

    What might be causing it?

    The TIA now operating with  ±5VDC.

    Thanks,