P2040/P2041 USB Specific FAQs

Document created by Omar Cruz Employee on Aug 6, 2012
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For P2041, if USB1 and USB2 ports are not implemented, what to do with the unused USB ports ie tie them to ground, 3.3V or leave them unconnected?

If USB is not to be used at all, keep the following USB signals floating: USB1_IBIAS_REXT, USB2_IBIAS_REXT, USB1_VDD_1P8_DECAP, USB2_VDD_1P8_DECAP, USB1_VDD_3P3 and USB2_VDD_3P3.

The following signals should be pulled-down: USB1_VBUS_CLMP, USB2_VBUS_CLMP and USB_CLKIN.

Also, pins USB_VDD_1P0 and USB2_VDD_1P0 must be tied to 1V or the platform voltage (whatever is the SOC core digital power supply)


If USB_VDD_3P3 must be connected to 3.3V, will the power sequence be same as other 3.3V (OVDD) (no special power sequence for USB_VDD_3P3)?

Even if PHY is not used, USB_VDD_1P0 must be tied to 1V or the platform voltage (whatever is the SOC core digital power supply), other pins can be left floating: USB1_IBIAS_REXT, USB2_IBIAS_REXT, USB1_VDD_1P8_DECAP and USB2_VDD_1P8_DECAP, USB1_VDD_3P3, USB2_VDD_3P3. If signals USB_VDD_3P3 and USB_VDD_1P8 are left floating, there is no need to take of power sequencing on these pins, only USB_VDD_1P0 must be a part of standard power sequencing requirements. If signals USB_VDD_3P3 and USB_VDD_1P8 are used (i.e. not left floating), power sequencing is to be done as under: Follow a minimum ramp time of 350us on USB_VDD_3P3(most regulators would give a 350us ramp time) and standard power sequencing on USB_VDD_1P0,USB_VDD_3P3. USB_VDD_1P8_DECAP would only have 1uF capacitor and is automatically tolerant of sequencing on rest of the supplies are sequenced properly. Also based on silicon validation:

  • There is no power down sequencing to be followed on the PHY. There requirements were added as a backup strategy in case the new regulator in the IP had a problem. We have tested this regulator, so no power down sequencing requirements is needed.
  • There is no need to supply any power to USB_VDD_1P8_DECAP, as the circuit is working fine.


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