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7/1/2025, 12:44:27 PM
>>2928092
>>2928093
>>eatmyass
If you power an op-amp from +/-15V, like a lot of datasheets specify at the top/bottom of the DC electrical characteristics table, then the op-amp will only function properly with inputs somewhat within those rails. If it's a rail-to-rail input op-amp, then it can basically go all the way, and there are some special op-amps that can go beyond, but generally there's a volt or two dropout. A value of +/-13V means it can go within 2V of the lower rail and 2V of the upper rail when powered from +/-15V, and it's pretty safe to assume that 2V of dropout will remain roughly constant at other voltage rail sizes. Some datasheets even have a graph of this. Like this misspelt one from my Philips NE5534 datasheet. These graphs are kinda useless because of the zoom and coarse gradations, it would be better if they graphed the difference between the rail and input voltage (e.g. 2V) instead of the total voltage.
Some op-amps have an asymmetry on this feature, the OPA1642 looks to be capable of measuring 0.1V below it's negative voltage rail, while has to be 3.5V below its positive rail. At the specified voltage.
>>2928093
>>eatmyass
If you power an op-amp from +/-15V, like a lot of datasheets specify at the top/bottom of the DC electrical characteristics table, then the op-amp will only function properly with inputs somewhat within those rails. If it's a rail-to-rail input op-amp, then it can basically go all the way, and there are some special op-amps that can go beyond, but generally there's a volt or two dropout. A value of +/-13V means it can go within 2V of the lower rail and 2V of the upper rail when powered from +/-15V, and it's pretty safe to assume that 2V of dropout will remain roughly constant at other voltage rail sizes. Some datasheets even have a graph of this. Like this misspelt one from my Philips NE5534 datasheet. These graphs are kinda useless because of the zoom and coarse gradations, it would be better if they graphed the difference between the rail and input voltage (e.g. 2V) instead of the total voltage.
Some op-amps have an asymmetry on this feature, the OPA1642 looks to be capable of measuring 0.1V below it's negative voltage rail, while has to be 3.5V below its positive rail. At the specified voltage.
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