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Kinetis K20, Flexbus, USB and ULPI interface question

Question asked by Sherry Sher on Oct 21, 2015
Latest reply on Oct 29, 2015 by Hui_Ma



I have 2 questions regarding a Kinetis K20 based microcontroller (specifically MK20FN1M0VMD12).

The reference manual for k20 family states on page 154 that "When USB is not used it the application, it is recommended that the USB regulator "VREGIN" and "VOUT33" pins remain floating."


Now my issue is that I am not using USB OTG, but I am using ULPI (to connect to a USB transceiver (with ULPI interface)). The pins used are:-


ULPI_DATA[7:0]                                                          For data

ULPI_CLK, ULPI_DIR, ULPI_NXT, ULPI_STP             For control signals

I have left the pins "USB0_DP" and "USB0_DN" unconnected and floating.


Question1> Does the above mentioned rule from pg. 154 of the reference manual still hold true? (meaning with this setup do I NEED to leave "VREGIN" and "VOUT33" floating? whats the worst that can happen if I power VREGIN with 5V?)

Question2> Is it safe to have "USB0_DP" and "USB0_DN" pins floating and not connected?



Many thanks in advance