AnsweredAssumed Answered

i.MX6 USB Pull Resistors

Question asked by Jarrod Cook on Jul 30, 2018
Latest reply on Aug 2, 2018 by Jarrod Cook



I am running my device as a gadget using the USB OTG port.  I have some special circumstance where i need to detect when my device is connected to another custom board even when the other custom board is NOT powered.  For this reason i can't simply detect the presence of VBUS.  So what was done is a 15K pull-down resistor was placed on the other custom board between GND and DP and a 100K pull-up resistor was placed on the i.MX6 board between DP and 3.7V so that when plugged together even when not powered we would be able to detect the change in the DP line from the 15K pulling the voltage to about 0.5V.  


However even when nothing is connected (DP floating with 100K pull-up) I am only seeing a little over 1V on the DP line instead of the expected 3.7V!

This leads me to believe that the DP line is somehow connected via an internal resistor on the i.MX6 to some other rail.  I have made sure the 200K switchable pull-up resistor is off in USBPHYx_CTRLn and the 15K should only be enabled in host mode i would think and i even tried explicitly disabling it using the USBPHYx_DEBUGn register, but still no difference.


Any idea what is going on here?  How can i perform this detection?


EDIT: Another thing i forgot to mention is that if i apply a voltage to VBUS with DP still in this floating state the voltage goes up to where to expected.  So it seems have something to do with no VBUS on the module, maybe this means it is not properly powered or something???