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TMDS181: TMDS181 DDC Lines

Oscar Zuniga
Prodigy 120 points
Part Number: TMDS181

Hi, 

We have implemented the TMDS181 4K HDMI Retimer to our design and have some concerns after noticing that the retimer would fail. We see that the retimer is working fine at first, however, it would eventually stop working . We have been switching different camera inputs into the retimer and are wondering if doing so is causing damage to the retimer regarding the DDC lines. Here's how we have the retimer DDC pins set up on our design (note, we are using pin strap and is close to the configuration as Figure 36):

1.) DDC_I2C _SRC connected to GND

2.) DDC_I2C_SNK connected to the cameras DDC_I2C lines and going to our receiver application

Here are the type of cameras we are using: 

1.) Regular HDMI camera 

2.) Custom HDMI Camera 

We are using the retimer as a sink side application. However, on our custom HDMI Camera, we decided to use the DDC_I2C lines as a way to communicate to the camera to obtain information. We are afraid that switching from a regular COTs camera to our custom camera might be damaging the DDC_I2C lines in the retimer and causing issues within the chip, thus leading to the chip to fail overall. Do you think that might be an issue? Also, could we, in theory, not have anything connected to the DDC_I2C_SRC/SNK pins of the retimer? Would it be possible to just bypass them?

Thanks

  • 0
    TI__Guru 60865 points
    Hi Oscar,

    Is the custom camera using the DDC lines at a voltage greater than 5V? The TMDS181 should not be affected by extra traffic on the DDC lines, this is common for HDCP enabled applications.

    The TMDS181 uses the snooping of the DDC lines to determine when to switch the clock ratio from 1/10 (HDMI 1.4B) to 1/40 (HDMI 2.0). If your application can set the clock ratio and transmitter terminations manually, you could bypass the DDC lines. What is occurring on a failing system?

    Regards,
    JMMN
  • 0 in reply to JMMN
    Prodigy 120 points
    DDC lines are not at a voltage level greater than 5V. We have implemented DDC snoop with success. And we have been able to connect to the camera and get video without the I2C_SRC and I2C_SNK connected. So, bypassing the DDC lines also worked for us. However, it's when we're connecting or disconnecting the camera from the retimer where we stop seeing the retimer chip fail. Question, could ESD from our custom HDMI cable and camera be affecting either the HDMI lines, I2C lines, or HPD lines to the retimer? We do not have ESD protection on any of those lines since we followed the development board. Thanks.
  • 0 in reply to Oscar Zuniga
    TI__Guru 60865 points
    Hi Oscar,

    Yes, you could be seeing damage from ESD. Do you have a local TI representative?

    Regards,
    JMMN