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ADA4254A gain behavior

Category: Hardware
Product Number: ADA4254A

We are using the ADA4254ACPZ as a variable gain amplifier.

Schematic:

Behavior that's problematic description:

1.  Vocm is 1.25 Volts

2. The input can saturate with V+ = 2.5 V and  V-  = 0V   

depending on the gain, the output can go to V+ = 5V and V-  = Gnd

3.  The disturbing issue is that the output goes to ground or near it, then the gain can be reset and the signal comes back.

Doesn't seem like overvoltage protection since the high voltages are + 28 V and - 28V

Is there something we're missing?  is there errata on this?



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[edited by: GenevaCooper at 5:57 PM (GMT -4) on 14 Sep 2022]
  • Note, the INPUT_ERR flag is being set when the output voltage saturates using higher gains. I'm thinking just disable gain reset , but it doesn't make sense that the in put _err is triggering, the inputs don't change and it's way below 28v.  So there's something inside the chip whereby the input error is being tripped when the output saturates... thoughts? Please?

  • Hi,
    I have moved this question about ADA4254 to the Instrumentation Amplifier community.  Someone here should be able to assist you.

  • Hi Adam,

    I think we've answered this offline, or is this a different issue?

    To summarize, the high input voltage capability of this amplifier makes it suitable for high voltage applications but we still need to take note of the input differential voltage capability. Although its input voltage range states that its capability is ranging from AVSS to AVDD-1, its output amplifier limits is only at AVSS+0.06 to AVDD-0.08.

    When you use the higher gain of the PGIA, with the input level you mentioned, this will violate the output amplifier limits - that will trip an error and reset in the part for protection.

    Regards,

    Kristine