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TMDS181: TMDS181 don't have output signals to FPGA

Thomas Gan1
Prodigy 70 points
Part Number: TMDS181

Hello TI experts,

I have used TMDS181 in my project. I meet a  critical issue in my debugging. You can refer to my block design diagram and schematic in the attachment. I can catch  a 148.5Mhz clock signal which sent from PC in TMDS181 input side, but I can't catch the  clock signal output from TMDS181 in  FPGA side. I used pin strap mode in my design.

My configuration as below:

1)  SIG_EN ( PIN 17)     with a  64.9k resistor  pull down

2) I2C_EN_PIN(PIN 10) with a 64.9k resistor  pull down

3) OE (PIN 42)  with a 4.7K resistor pull up to 3.3V

4) EQ_SE_A0 ( PIN 21 ) NC

5) A1 (PIN 27) NC

6) VSADJ (PIN 22)  with a 7.06K resistor pull down

7) TX_TERM_CTL (PIN 36) NC

8) PRE_SEL (PIN 20) NC

9) SWAP_POL (PIN 1) NC

10) SPDIF_N (PIN 45) with a 470K resistor pull down.Intput_card schematic.pdfCard block diagram.pdf

Thanks a lot.

  • 0
    TI__Guru**** 166411 points

    Hi,

    Does the FPGA require to be AC-coupled? If FPGA require to be AC-coupled, do you have external termination network on the TMDS181 output?

    From the schematic, 

    The OE pin has an internal weak pullup, please have 0.22uF pulldown on the OE pin

    For the sink side, do you have the 47k pullup on SDA_SNK and SCL_SNK?

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 70 points

    Hi David,

    Thanks your quick response.

    1) I used DC-coupled in FPGA side.

    2) I used external 4.7K pull up  at OE pin  and connected to CPLD for power on reset.

    3)  SDA_SNK and SCL_SNK with pull up.

    My current critical issue is PC have sent clock signal to TMDS181 but it don't have signal output to FPGA .

    Do you have any suggestion why TMDS181 don't have output ?

    Thanks  a lot.

  • 0 in reply to Thomas Gan1
    TI__Guru**** 166411 points

    Hi,

    If the HPD_SNK is driven high, then it depends on the termination structure inside the FPGA. Does the FPGA have 50 ohm termination to 3.3V?

    If the FPGA input requires to be AC-coupled, then you would need the external 50ohm termination to 3.3V between the TMDS181 output and the AC coupling caps.

    Thanks

    David 

  • 0 in reply to David (ASIC) Liu
    Prodigy 70 points

    Hi David,

    The issue is fixed after add external 50ohm termination to 3.3V.  Thanks your great support.