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iMX25 USB PHY Dm Dp voltage levels (unpowered)

Question asked by Gordy Carlson Employee on Oct 27, 2014
Latest reply on Oct 28, 2014 by Gordy Carlson


Customer is designing the mx25 in a system that utilizes a ‘smart’ battery charger.  He routes D+/D- from the input port of the device to both the charger and MX25.  The charger listens to D+/D- and complies to the BC1.2 spec.


The system will operate in a few different modes where the mx25 may or may not be powered (the charger has dynamic power path management to route HOST power to our system or directly to the battery or both.).


As I understand the charger, at initial plugin it will apply 600mV bias voltages to determine the state of the D+/D- lines to determine current limits.

Does 600mV on USBPHY1_DP/USBPHY1_DM matter to an unpowered MX25?

    1. Does the answer depend on whether state of USBPHY1_VBUS?
      1. USBPHY1_VBUS = 0V OR
      2. USBPHY1_VBUS = 5V from usb bus….. rest of MX25 would remain at 0V.