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ISOUSB211: Isolated Self-powered peripheral

Mike Nudelman
Intellectual 285 points
Part Number: ISOUSB211
Other Parts Discussed in Thread: TM4C1294NCPDT

Trying to make it work with the TIVA uC. The TM4CF1294 

We do have a TIVA-based conntroller board. We decided to isolate the USB as in a few places in Europe/Asia the USB gets damaged when plugged into computers.

I have just ordered the eval board for the ISOUSB

The device we have has been sold throughout thr world. Since we had started using USB instead of RS-232, every once in a while the DM/DP lines get damaged. I suspect it has to do with some isolated Power Supply-powered laptops plugged into it. They float at 1/2 Mains. But in the US it seems to be mostly fine. We have 120V. So, we decided to try to isolate the device's USB.

I have just ordered the eval kit, has not come yet.

I am trying to understand, first, what power I will be dissipating (it would be nice to have max powers as many chip mfr show) and if it is safe to use VBUS to power the whole upstream side (no overheat) as my space to accomodate the isolator on the existing controller is limited; second, if it is OK to use just 3.3V to the downstream (device connected) side and, third, what do I use as VBUS signal to the device? V1OK?

I am limited with the space on the board so i would like to use as few external components as possible 

Thanks. Well, not really a concern...I take it, the connector shell should now be isolated from the device's enclosure (until now it's been connected to it).

  • 0
    TI__Genius 9640 points

    Hi Mike,

    Thanks for reaching out detailed inputs.

    There are different available options to power ISOUSB211. These options are provided primarily for the power dissipation itself. These details are provided in Section 7.3.1 in the datasheet.

    Once you've understood the power supply options, Section 8.2 and its subsections in the datasheet explicitly illustrates the power calculations with different supply configurations in detail.

    If you have any specific question from the above-mentioned sections from datasheet regarding your application, feel free to reach out

    Regards
    Varun

  • 0 in reply to Varun Kumar
    Intellectual 285 points

    I get the power versions. 

    Two questions:

    1. is there any detriment in using resistors to dissipate power vs LDO/DCDC providing 1.8V on either side? Performance degrading, etc?

    2. Again, what do I use as the VBUS signal for the TIVA processor on the Downstream side? is V1OK good for it? If not, how do I let the microcontroller USB know the device detected the VBUS on the upstream side?

    My current non-isolated circuitry is below. First the Type B connector, where VBUS is formed (protected with a Zener and a resistor), and then below is fed to PB1 pin of the TIVA CPU (dedicated VBUS pin).

  • 0 in reply to Mike Nudelman
    TI__Genius 9640 points

    Hi Mike,

    I'm not fully aware of your application so I don't get the full clarity your questions above. Please provide detailed inputs for us to get the full context.

    Mike Nudelman said:
    1. is there any detriment in using resistors to dissipate power vs LDO/DCDC providing 1.8V on either side? Performance degrading, etc?

    I don't understand the use of resistors and for what exatly.

    Mike Nudelman said:
    2. Again, what do I uses as the VBUS signal for the TIVA processor on the Downstream side? is V1OK good for it? If not, how do I let the microcontroller USB know the device detected the VBUS on the upstream side?

    That's the very purpose of V1OK as mentioned in datasheet pin functions. So yeah, you can use V1OK.

    Regards
    Varun

  • 0 in reply to Varun Kumar
    Intellectual 285 points

    1. These resistors.

    2. The application is based around a TI part, TM4C1294NCPDT microcontroller. It has a USB interface which my application uses for communication as a Device (Peripheral). The microcontroller's USB determines the device is connected to a Host by monitoring the VBUS (as any USB2.x would). Now that I am using your ISOUSB211 isolator, there is no specific VBUS signal that this isolator outputs, that is described in the datasheet as the VBUS output to the microcontroller (now that the microcontroller is physically isolated from the Host).

    My question is: what should I be using as the VBUS? Can V1OK be used in this capacity? 

    The TM4C is a TI part, so you should be aware how to connect the two chips together.
    If V1OK can be used, I guess I have to convert it to 5V, as PB1 when configured as VBUS input, requires 5V level.

    I am satisfied I can use V1OK, but nowhere in the datasheet it explicitly says it can be used as VBUS. Perhaps the wording should be modified (and, yes, it is understood it won't provide the 5V power that VBUS typically supplies, but will provide the connection indication function)

  • +1 in reply to Mike Nudelman
    TI__Genius 9640 points

    Mike,

    Mike Nudelman said:
    am satisfied I can use V1OK, but nowhere in the datasheet it explicitly says it can be used as VBUS. Perhaps the wording should be modified (and, yes, it is understood it won't provide the 5V power that VBUS typically supplies, but will provide the connection indication function)

    Yes, I think this resolves your issue. Perfect!

    Mike Nudelman said:
    1. These resistors.

    There is no performance degradation by using these resistors.

    Regards
    Varun