The Icc USB current specified in the FX3 Datasheet determines the power consumer by the USB core. A maximum value is specified in the datasheet (refer to Table 8). This is the maximum value and the actual value can change dynamically. If the FX3 is enumerated as a high speed device rather than a super speed device, the current consumed by the USB core is expected to reduce. This also depends on the power state the device is in.
If the FX3 is enumerated a super speed device, will the current consumed by the USB core be related to the real-time USB data speed ?
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Focusing only on the USB side of the application, If you are referring to the power consumed by the USB core only during the data transfers, then the power consumption is dependent more on the duration of the data transfer in the application and less on throughput of the transfer.
If there is a continuous streaming of data, power consumption will be higher, compared to when there is less amount of data transfers, in the same time duration.
Considering throughput of the USB interface: There may be many factors responsible for the throughput (the host controller, host application, and firmware implementation). There will be a minimal variation in power due to the change in throughput.
Also, do refer to this KBA EZ-USB® FX3™ Power Consumption – KBA85505