SN75DP159: SN75DP159 there no output video signals

naftali sabag

Part Number: SN75DP159
Other Parts Discussed in Thread: TS3DV642, , TDP158

Tool/software:

In our design, we connect the HDMI connector via AC capacitors , to the TS3DV642 MUX component, and we connect the MUX output to the SN75DP159 inputs without AC capacitors, and we connect the SN75DP159 output to the TS3DV642 MUX input. We checked all the SN75DP159 pins and everything according to the DATASHEET,

There is a video signal at the input to the SN75DP159 , but all the video outputs signals are at 0 volts.

I checked all the voltages for the component with an oscilloscope, both 3.3V and 1.1V are all normal. I checked the quality of the video signals at the input, the signals are as expected.

The component is in pin configuration mode and not I2C configuration.

What could be the reason for this?

Attached the electrical schematic.KVM 4X2 - DOCF605REV02.pdf

6 months ago

0 David (ASIC) Liu 6 months ago

TI__Guru**** 176811 points

Hi,

Looking at the schematic, it looks like the DP159 output is AC coupled as well, can you please verify if this is the case? If this is the case, then you would need the 49.9 termination network to 3.3V between the DP159 output and the AC coupling capacitor.

Thanks
David

0 naftali sabag 6 months ago in reply to David (ASIC) Liu

Prodigy 20 points

the DP159 output is not the AC coupling capacitor , the output connects directly to TS3DV642 12-Channel 1:2 MUX/DEMUX D[3:0]±A. or to D[3:0]±B.

Please follow the schematics.

+1 David (ASIC) Liu 6 months ago in reply to naftali sabag

TI__Guru**** 176811 points

Hi,

I was looking at this portion of the schematic, it appears the output of the TS3DV642 (U34) goes to TDP158 (U111) which has AC coupled input. So DP159 output is AC coupled, is my understanding correct in this case?

Thanks

David

0 naftali sabag 6 months ago in reply to David (ASIC) Liu

Prodigy 20 points

Thanks for Quick response

I did a test and disconnected U36 and U12, and yet the output of the U65 SN75DP159RSB component did not have a video output, and all the outputs were at 0 volts.

0 David (ASIC) Liu 6 months ago in reply to naftali sabag

TI__Guru**** 176811 points

Hi,

Are you physically connecting DP159 output to both U12 and U36? I would not recommend to do this because the reflection would degrade the output signal integrity.

When you remove U12 and U36, did you probe the DP159 output with the probe terminated to 3.3V?

Thanks

David

0 naftali sabag 6 months ago in reply to David (ASIC) Liu

Prodigy 20 points

Thanks for Quick response.

No, the probe not terminated to 3.3V.

Question: If I install a 0 ohm resistor in place of the AC coupled capacitor at the input to the TDP158 component (U111), will that solve my problem?

0 David (ASIC) Liu 6 months ago in reply to naftali sabag

TI__Guru**** 176811 points

Hi,

The DP159 output is a current mode driver, so it would expect to see 50ohm termination to 3.3V to generate the waveform.

If you replace the AC coupling capacitor with 0ohm resistor, it will not work because the TDP158 input termination is 50ohm to GND, not 50ohm to 3.3V. You will have to provide the external 50ohm to 3.3V termination between the DP159 and the AC coupling capacitor.

Thanks

David

+1 naftali sabag 6 months ago in reply to David (ASIC) Liu

Prodigy 20 points

Thank you very much for your help and support. Your solution solved the problem, now the video works.

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SN75DP159: SN75DP159 there no output video signals