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AM335x : unused pins of USB ports

Devin Park
Expert 5965 points

Hi,

Regarding the AM335x ZCZ, I wonder how we treat VSSA_USB when USBs are not used.

From our checklist site, I know at least VDDA1P8V_USB should be connected to a 1.8V supply. I think it's because PER_PLL is powered from VDDA1P8V_USB0. So if 1.8V is not supplied, then AM335x will not boot properly, is it right?

If USB0 or USB1 is not used...
      • Connect the respective VDDA1P8V_USB terminal to any 1.8-V power supply and respective VDDA3P3V_USB terminal to any 3.3-V power supply. If the system does not have a 3.3-V power supply, the VDDA3P3V_USB terminal may be connected to ground.The respective VBUS, ID, DP, and DM terminals may be connected to ground or left floating.
        • The OTG_PWRDN and CM_PWRDN bits in the respective USB_CTRL register can be used to power down the unused USB PHY to minimize power supply leakage current. These bits default to the powered-up state after the AM335x device has been reset. The USB PHY can be powered down by setting both of these bits to "1".
    • The respective CE terminal should be left floating.

 

But there is no mention about VSSA_USB. should it be connected to GND? Otherwise, may it be left floating?

 

Thanks,

Devin