iMX8MPlus and PTN3366 Compatibility Issue

[CSchutte]

Hi, 

I have designed a SBC project which uses the i.MX 8M Plus CPU. I need to convert the HDMI outputs to LVDS which required me to shift the HDMI outputs from 1.8V to 3.3V. To do this I chose the PTN3366.

Now that I have received boards I am finding that there is an issue with the HDMI signals. The PTN3366 calls for AC coupling on all differential pair inputs as shown by the below screenshot from the datasheet:

However, I am now finding that when I include AC coupling capacitors on my HDMI outputs from the iMX8, the HDMI signals disappear. If I short past the capacitors directly to the PTN3366 then the signals re-appear. It looks like the HDMI signals need some kind of sink resistance in order to be driven that the capacitor is blocking it from seeing.

Am I correct in thinking that the iMX8MPlus is looking for a sink resistance to drive the signals? If so, how can I make this work with the PTN3366 which requires these series capacitors?

Thanks!
Connor

[JorgeCas]

Hello, I hope you are doing well.

Am I correct in thinking that the iMX8MPlus is looking for a sink resistance to drive the signals? If so, how can I make this work with the PTN3366 which requires these series capacitors?

It could be possible but it is strange since those capacitors are needed as is mentioned on datasheet.

Did you try to change equalizer settings?

Did you consider squelch function? Where IC only operates when input signal is above minimum threshold (VRX_DIFFp-p).

Best regards.