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# ISOUSB211: USB device current consumption seen by host

Part Number: ISOUSB211

Dear TI,

When a USB device is connected to a computer through ISOUSB211, what is the VBUS current consumption seen by the host during USB device enumeration?

Thanks,

Anwar

• Hi Anwar,

Thanks for reaching out.

The current consumption depends on multiple factors and actual implementation, i.e., if ISOUSB211 is used at the host or device, if device is self-powered or bus-powers, if device is a FS or HS device among other things. I will provide an example use case and let you know the expected current consumption on VBUS.

Let's consider the use-case in Figure 10-2 of ISOUSB211 datasheet where ISOUSB is used with a self-powered device. Let's also assume the device is a FS device. In this case, the total current of VBUS pin on USB port will be a sum of currents of VBUS1 and V1P8V1 in FS mode. This current is going to continuously vary based on the whether it is transmitting, receiving or idle and will range between 7.4mA and 15.3mA as stated in the datasheet (ignoring the current of V1P8V1 of 0.55mA).

Under the same conditions if the device is an HS device, then total current of VBUS pin on USB port will be a sum of currents of VBUS1 and V1P8V1 in HS mode. This current can also continuously vary based on the whether it is transmitting, receiving or idle and will range between 10.5mA and 96mA as stated in the datasheet.

If the device were to be bus-powered instead of self-powered, then the total current will also include current into VBUS2 and VCC2/V1P8V2 as well. Since an isolated power supply will be used to power side2 of ISOUSB211, its efficiency will also play a role in determining the amount of current that will be visible on VBUS pin of USB port.

I hope the above calculations provided you with some clarification on how to calculate current consumption of ISOUSB211 for your application. Let me know if you have any other questions, thanks.

Regards,
Koteshwar Rao