AnsweredAssumed Answered

Low voltage on eDP AUX channel drivers

Question asked by Tony Bryant on Jul 2, 2020
Latest reply on Jul 5, 2020 by igorpadykov

Problem: Unreliable EDID/setup negotiation with eDP panel on our iMX8MQ board.   (It works only 70% of the time.  When it works, everything works fine until the next power cycle)


Probable cause:   Low voltage on AUX channel output.   Approx 100mV Peak-to-peak with a 300mV centre (i.e. well out of spec).   Signal back from panel is the expected full 1V p-p.   


My Circuitry:  AUX lines connected to panel via simple series 0.1uF caps, with 100K pull up/down resistors.  Trace are 50 Ohm impedence, and are fairly short.   Panel is connected by a 3" microcoax cable via the standard IPEX connectors.


Have checked:   HDMI_AVDDIO = 1.8V   HDMI_AVDDCORE and HDMI_AVDDCLK = 0.9V


SW:  I'm using uboot 2018.07,  ATF v2.0,  Freescale Linux 4.14.98,  everything else is functional.


The question I have is:   Is there any power gating that needs to be enabled to get the full output voltage on the AUX pads?


Also,  which power pad supplies the power to the AUX pads?  HDMI_AVDDIO?