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Tool/software:
Hi team,
This is FAE Jayden, ZTE is evaluating OPA4277UA/2K5 and they have some questions about this device:
Many thanks
Brs
Jayden
Please see answers below:
Where the output ends up with the input floating depends on the direction of the input bias current (IB). If the input bias is positive (IB direction is into input terminal), the input will go down, thus driving the output towards negative rail. For a negative IB (IB current comes out of input terminal) the output will be driven close to positive rail.
However, in case of OPA277 with the internal input bias cancellation, the IB may be of either polarity (see +/- sign below). In such a case, depending on the actual IB direction, the output will end up close to either rail.
How close to either rail the output may end up is shown in the output voltage swing range (see below) - 0.5V above (V-) or 1.2V below (V+).
If input of one channel is left floating, the other channels should not be effected. However, the output of the channel with floated input will saturate at one of the rail, which may result in the increase of quiescent current, IQ. For this reason, it is recommended to always bias the unused channels at mid-supply (e.g. using resistor divider between the rails) so the input and output stay within specified linear range.