TFP401PZPEVM: When no HDMI signal - ODCK problem

Krzysztof Szawerna

Part Number: TFP401PZPEVM
Other Parts Discussed in Thread: TFP401

Hello.

Problem occure when HDMI input signal is not connected. In this state ODCK signal should be not active. But TFP401PZP generate some very strange vaveform of ODCK. I don't know why and where is the problem.
I checked PCB and everthing is OK. When I connect HDMI signal TFP401PZP work properly. But after disconnetctig HDMI, ODCK signal is again wrong generated. When HDMI is not connected ODCK should be not active - low.
Somethimes ODCK is just stable LOW when no HDMI input, but somethimes it is unexpected wave.
This behavoir is not described in documentation.

over 3 years ago

0 Krzysztof Szawerna over 3 years ago

Prodigy 10 points

This is ODCK when no HDMI connected.

0 David (ASIC) Liu over 3 years ago in reply to Krzysztof Szawerna

TI__Guru**** 179081 points

Hi,

Are you leaving the /PDO unconnected? When PDO is left unconnected, an internal pullup defaults the TFP401/401A to normal operation.

You can tie the SCDT pin directly to the TFP401/401A PDO input to power down the output drivers when the link is inactive (no HDMI input).

Thanks

David

0 Krzysztof Szawerna over 3 years ago in reply to David (ASIC) Liu

Prodigy 10 points

Hi, this is good solution and it works well.
Thank you very much.
However it is interesting when normal operation and no HDMI input all signals RGB(24),Hs,Vs,De are not active, but ODCK sometimes (not always) generate this strange wave. Also this behaviour is not described in documentation. In my opinion should be!

Kris

0 David (ASIC) Liu over 3 years ago in reply to Krzysztof Szawerna

TI__Guru**** 179081 points

Kris

With no HDMI clock input, the internal PLL which generates the ODCK is free running and its frequency can't be guaranteed. So it will be a good idea to use the /PDO to turn off the output when there is no input.

Thanks

David

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TFP401PZPEVM: When no HDMI signal - ODCK problem