AD8220 output voltage

I am running the AD8220BRMZ from +/-5V, with a gain set to 100 and the REF pin set to 2.5V. I notice that the output swing limits at 4.70V despite the datasheet indicating that I should get 4.85V as a minimum. Am I interpreting the datasheet correctly? This happens with a difference input of 22mV which is as expected i.e. (0.022V x 100) + 2.5V = 4.7V. The common mode max is 2.5V.


Another question I have is as follows. If I continue to increase the difference input beyond 22mV, the output remains clipped at 4.70V as expected but then above 40mV, the output begins to come down. At 45mV the output is 4.22V and at 49mV the output is 3.86V. Does anyone know what might be going on here?


Any comments appreciated. Thanks.

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  • Hi Paul,

    I believe figure 30 was measured with no load on the output. You can see in the +5V specifications table that the output swing goes up to 4.85V, but also that is for a 10k load. 2k is a heavier load and the output will saturate earlier. Figure 35 shows the approximate behavior, but the part is loaded to 2.5V. In terms of output current near the top rail, 2k to ground looks like 1k to 2.5V. The 25°C value at 1k looks pretty close to 4.7V to me.

    I hope this helps.

    Best regards.

    Scott

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  • Hi Paul,

    I believe figure 30 was measured with no load on the output. You can see in the +5V specifications table that the output swing goes up to 4.85V, but also that is for a 10k load. 2k is a heavier load and the output will saturate earlier. Figure 35 shows the approximate behavior, but the part is loaded to 2.5V. In terms of output current near the top rail, 2k to ground looks like 1k to 2.5V. The 25°C value at 1k looks pretty close to 4.7V to me.

    I hope this helps.

    Best regards.

    Scott

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