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TUSB3410: bMaxpower

Kenji Ohno1
Genius 5095 points
Part Number: TUSB3410

Hi Team,

I got some question about TUSB2046 from my customer.

The setting value of bMaxPower on the Configuration Descriptor is 0 mA. However, the measured value is 0.187 mA.

This current consumption occurs because of a pull-down resistor on the Vbus circuit.

In the compliance test, consumption current is required to be less than or equal to the set value of bMaxPower.

Please tell me below.

① Would you pass if you comply with the compliance test?

② Is there any problem in actual use?

③ Is my understanding of bMaxPower's setting incorrect?

Best Regards,

Kenji

  • 0
    TI__Expert 7395 points
    Kenji-san,

    Can you please confirm what part number you are referring to? Is it TUSB3410 or TUSB2046. I am confused since both part numbers are being mentioned.

    Regards,
    Jorge
  • 0 in reply to Jorge Llamas (SWAT)
    Genius 5095 points
    Jorge-san,


    I'm sorry. I made a mistake.
    TUSB 2046 is correct.

    Best Regards,
    Kenji
  • 0 in reply to Kenji Ohno1
    TI__Expert 7395 points
    Kenji-san,

    bMaxPower value should change based on the selected configuration. If you are selecting a bus-powered implementation then bMaxPower will be set to 0mA indeed.

    Can you please clarify what that detection circuit is? What is the purpose of that block? If you can provide detailed schematics showing your TUSB2046 implementation, that would certainly help.

    Regards,
    Jorge
  • 0 in reply to Jorge Llamas (SWAT)
    Genius 5095 points

    Jorge-san,

    The circuit detects VBUS and makes a sequence of IC power ON / OFF and reset.

    Since VBUS is connected to Digitra, it consumes a little current.

    As the reference circuit posted by TI also leads to the base of the transistor, I think that current will flow slightly, how do you think?

    Since it is set to bMaxPower = 0 mA, is this configuration not to pass the compliance test?

    · Does the configuration of TI's Reference Circuit pass the compliance test?

    · If you pass it, will you pass the compliance test even if it is actually flowing up to what mA?

    I got a detailed circuit diagram from the customer, but I will send it if necessary. Please contact me locally.

    Best Regards,

    Kenji

  • 0 in reply to Kenji Ohno1
    TI__Expert 7395 points
    Kenji-san,

    I am not sure about what specific configuration or board was used to get the compliance logo for this device.
    However some minimal current draw on VBUS is acceptable for self-powered configurations, precisely because of VBus detection mechanisms.

    Some other USB Hub devices in our portfolio, like the TUSB4041, have a terminal for VBus detection and it has been able to pass all the compliance tests while drawing around 60uA from VBus on a self-powered configuration ( bMaxPower = 0 )

    I have no exact data about what would be the maximum range allowed; I would recommend to contact the USB-IF for details on this.

    Regards,
    Jorge
  • 0 in reply to Jorge Llamas (SWAT)
    Genius 5095 points
    Jorge-san,

    Thank you for your reply.
    Your answer was very helpful.

    Best Regards,
    Kenji