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TMDS442: PCB LAYOUT GUIDELINES FOR TMDS442

Chandana Tadipaneni
Intellectual 440 points

Part Number: TMDS442

Hai,

Can anyone share pcb layout guidelines for TMDS442. and i have other question also if i make 2 layer pcb for TMDS442 switcher instead of 4 layer what will be the issues araised? what are precautions to be taken for perfect working of board.

Thanks & Regards,

Chandana.

  • 0
    TI__Guru**** 155220 points
    The high-speed TMDS inputs are the most critical paths for the TMDS442. There are several considerations to
    minimize discontinuities on these transmission lines between the connectors and the device:
    • match trace length of he TMDS differential signal
    • The TMDS differential inputs should be layout in the shortest stubs from connectors directly
    • Maintain 100-Ω differential impedance into and out of the TMDS442
    • Keep an uninterrupted ground plane beneath the high-speed I/Os
    • Keep the ground-path vias to the device as close as possible to allow the shortest return current path

    if you have only two layer, you may have interrupted ground plane beneath the high-speed I/Os, will cause reflection or other signal integrity issue
  • 0 in reply to Brian Zhou
    Intellectual 440 points

    Thanks for the reply!

    Presently i am using 2 layer board for TMDS442 Switcher. I am facing a different problem

    1) When i am using my laptop as the input source with supported resolution rate it is displaying at the sink port but after sometime it's not switching to sink port. when i checked the signal voltage at HDMI connector pins every pin voltage is as same as in previous working condition but HPD pin is going low and IC is heating too much.

    2) When i connected a mini-pc as my input source even though the ic's gets heated too much input is displaying on the sink port. Unlike laptop , this mini-pc is displaying continuously without any disturbance.

    3) When ever the input source is displaying i used to keep heatsink on IC , then input is displaying on the monitor.

    4) MOST IMPORTANT POINT:  All the inputs sources such as laptop, mini-pc, camera all are working fine when pcb is outside of enclosure that means in free space, but when ever i fix pcb in enclosure above issues are seen. Then what will be the reason for this? and also i found that HPD pin of source is going low even though source is on that means it is not in sleep mode. why?

    These are the issues i came across. Do you have any solution or idea about these? Please revert as soon as possible.

    If you want i can share you design files also.

    Thanks & Regards,

    Chandana.

  • 0 in reply to Chandana Tadipaneni
    TI__Guru**** 155220 points
    seems has heating issue, can you measure temp on device surface?
  • 0 in reply to Brian Zhou
    Intellectual 440 points

    But can you tell me how can i measure temperature?

  • 0 in reply to Chandana Tadipaneni
    TI__Guru**** 155220 points
    you can use thermos gun to measure, did you have a good soldering r thermo pad ?
  • 0 in reply to Brian Zhou
    Intellectual 440 points

    Thanks for the reply. I used heatsink it's working fine for all the inputs. But, there is a problem when only one output port is connected that means

    1) when ever i am using only first output port for displaying input and keeping second output port ideal without using at that time we are facing some issues. inputs are not displaying at the first output port properly.

    2) But same case when second output port is using and first output port kept ideal then there is no issue with displaying inputs.

    3) When we use both output ports then there is no problem with first and second output ports all the inputs are displaying on the monitors.

    we don't know why this is happening. Do you have any idea about this?

  • 0 in reply to Chandana Tadipaneni
    TI__Guru**** 155220 points
    how do you soldering thermo pad ?
  • 0 in reply to Brian Zhou
    Intellectual 440 points

    As we are using two layer PCB board. we soldered thermal pad at back side of the board using lead.

  • 0 in reply to Chandana Tadipaneni
    TI__Guru**** 155220 points
    two layer board may has issue. can you send layout to us for review?