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TMDS351 issue-help needed

Ivan Song
Expert 3145 points
Other Parts Discussed in Thread: TMDS351, TMDS361

Hi,Team,

Customer's TMDS351 schematic as attached.

2364.hdmi switch_wld.pdf

Problem descriptions:

1)SOURS1,2,3 are connected to TMDS351. Host can recognize SOURS1 first time.

When switch to other channel and back to SOURS1, Host can not recognize it.

Checked the PIN19 of CN9 at SOURS1 port, the voltage is 2.5V, it is not down to 0V. That's why host can not connect to it second time.

SOURS1(CN9)  PIN19,   R127  1Kohm pulling up, 

SOURS2(JP2)  PIN19,   R101  1Kohm pulling up, 

SOURS3(JP3)  PIN19,   R110  1Kohm pulling up, 

2) When remove 1Kohm(R127) or change it to 10Kohm, the host can reconnect to SOURS1 normally everytime.

In order to be compatible with other vendor, they have to put 1Kohm at PIN19 of each SOURSx port.

Can you help have a look at  their schematic and comment about what is the correct schematic or Resistor value for TMDS351?

Thank you very much.

 

regards,

Ivan

 

  • 0
    TI__Expert 6745 points

    Ivan,

     

    If you look at the spec of the HPD pin of the TMDS351, you will see that our sink current is around -100 uA to drive between GND and 0.4V.  The 1k pull-up is too small for this amount of specified drive strength.

  • 0 in reply to Ken Shaw
    TI__Expert 3145 points

    Hi,Ken,

    Many thanks for your quicky response.

    Yes, we checked datasheet page9, The TTL VOH, sink current is -100uA.It seems a 47Kohm resistor is suitable for the TMDS351.

    But in TMDS351 datasheet page19,  it recommends to use 1Kohm resistor. And in page17, we got belo informaition,

    The HPD circuits are powered by the 5-V supply. They provide 5-V TTL output signals to the SOURCE with a
    typical 1-kW output resistance. An external 1-kW resistor is not needed here. The HPD output of the selected
    source port follows the logic level of the HPD_SINK input. Unselected HPD outputs are kept low. When the
    device is in standby mode, all HPD outputs follow HPD_SINK. A 1-kW resistor to ground keeps all HPD outputs
    low in standby mode if a fixed low state is preferred.

    Can you suggst what we do is the best choice for TMDS351?   47Kohm pullinig up or  just keep it NC?

    Regards,

    Ivan

  • 0 in reply to Ivan Song
    TI__Expert 6745 points

    In our evaluation module for the TMDS361, I have selected a FET to provide the 5V HPD output voltage driven from the device.

    The 1k resistor is a series resistor that is required by the HDMI spec.  The description on page 19 actually a series 1k resistor from the 5V input directly to the HPD output. and not driven by the device.  BTW, you will also note that our device HPD output has this 1k series resistor internally connected.

     

    The TMDS351 has a VDD pin that is used to power the HDP interface.  If you do not need the performance of the 361, then this is a good alternative

  • 0 in reply to Ken Shaw
    TI__Expert 3145 points

    Hi,Ken,

    Customer still has problem about TMDS351. I will send email to you offline.

    Regards,

    Ivan