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AM3352: Inquiry about Maximun Input current value for USBx_VBUS pin

Takayuki Miyazaki
Genius 10120 points
Part Number: AM3352

Hi Experts,

Our customer is developing the module board with AM3352, customer is using USB signals as internal signals. For this board, AM3352 is working as USB device.

Regarding USBx_VBUS pin, customer would like to clarify following points.

  1. Maximun Input current value for this pin
  2. Minimum input voltage value to detect VBUS connection

The reason why customer is asking above questions is,

According to “16.2.7 USB Controller Host and Peripheral Modes Operation” in TRM,  there are following descriptions. I believe it is typo, I mean it is not “Not” but “Note”. And then, this customer has encountered the voltage-step issue because customer used the inverter device which has DC output current=25mA for USBx_VBUS pin.

Can I have your expert’s advice/comments on this inquires, please?

 

Best regards,

Miyazaki

  • 0
    TI__Genius 10120 points

    Hi team,

    Can I have your advice/comments on customer&s inquiries, please?

    Best regards,

    Miyazaki

  • 0 in reply to Takayuki Miyazaki
    TI__Guru 62835 points

    The answer to question 2 is correctly described in the TRM. VBUS must be greater than 4.4V to be considered valid.

    The USB PHY implemented in AM335x was designed to operate with functions and limits defined by the USB OTG specification. The USB OTG specification defines operational modes where VBUS can be sourced by the PHY.  However, this operation should not occur unless software specifically attempted this operation.

    The PHY also includes a charger detect function that is compliant to the USB Battery Charging Specification, Version 1.1. The battery charging function is enabled by default, which means it will source current to the data signals as defined in the specification to determine if a charger is connected.  However, I would not expect the battery charging function to source VBUS.

    There may be some current leakage paths that allow VBUS to consume current during power supply ramp, but I would not expect VBUS to consume any significant current during normal peripheral mode operating conditions.  The input impedance of VBUS should be high enough that a 1k resistor could be inserted in series with the VBUS signal connecting to the AM335x VBUS pin, without affecting its operation.

    Are you saying a 25mA CMOS inverter is not able to drive VBUS to a potential greater than 4.4V?  If so, what is the voltage of the CMOS inverter power source?  They need a 5V power source for proper operation.

    Regards,
    Paul

  • 0 in reply to peaves
    TI__Genius 10120 points

    Hi Paul,

    Thank you for your comments. I shared your comments with this customer.

    I'd like to wait for customer's feedback for a while.

    Best regards,

    Miyazaki