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OMAP-L137 USB design (I/O signals)

paddu
Intellectual 915 points
Other Parts Discussed in Thread: OMAP-L137

 

Hi,

I need some help with USB design.

The OMAP-L137's USB user guide SPRUFM9H

pg17 "2.2 Signal Descriptions" mentions that "USB0_ID pin should be either connected to ground or left floating".

 

Whereas, in Spectrum's OMAP-L137 EVM schematic sheet 6, 

the USB0_ID is connected to "DSK_3V3" through NO-POP resistor,

I know  NO-POP means not populated, but don't understand why USB0_ID is connected to "DSK_3V3"?

 

When using using OMAP-L137 USB as a device only mode, is it ok with the below connection 


 

 USB0_ID       -> floating

 USB0_VBUS -> pull-up to 5V with 1K ohm

 

Please let me know if there is any reference circuit for USB(2.0) Device mode.

 

Regards.

 

  • 0
    TI__Expert 8785 points

    paddu said:

    When using using OMAP-L137 USB as a device only mode, is it ok with the below connection 

     USB0_ID       -> floating

     USB0_VBUS -> pull-up to 5V with 1K ohm

    Your connection looks fine.  As confirmation, the ID pin needs to be left floating for device-only mode. 

    --Christina

  • 0 in reply to clam
    Intellectual 915 points

    Thank you,

    If possible could you please let me know why the USB0_ID pin connected to DSK_3V3 in the EVM schematics.  

    Regards.

  • 0 in reply to paddu
    TI__Expert 8785 points

    Previously, I believe it was communicated to pull the pin high for device-only mode.  However, it was later found out that the correct way to hook up the ID pin for device-only mode was to to leave the pin floating.  Therefore, since the EVM was based on the previous information, it still has the option to pull it high.  The schematics were updated to say "DNP" the pull-up resistor on the ID pin. 

    Even if the ID pin was hooked up correctly, it is still possible to override the ID pin values from within the PHY.  In the register SYSCFG[CFGCHIP2], there is a field called USB0OTGMODE.  In that field, you can force the controller to ignore the ID pin and operate only in device mode.

    --Christina