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SN75DP139 terminal resistance

Jason Shen
Intellectual 1965 points
Other Parts Discussed in Thread: SN75DP139

Dears

I have a customer using SN75DP139 between Intel CPU and a DVI connector, and find some failure. one of the output channel have lower signal amplitude is the phenomenon. and we also checked the DC level of the signal, and the failure channel have like 1.6V DC offset, but the normal channel have 2.9V offset. 

we also try to add 50Ω terminal resistance on the output, but the DC level is still 1.6V, seemed the IC draw lots of current. 

so is there some suggestion in your side about this failure?  customer do not add the 50Ω input terminal resistor, does this have impact.

and also they do not connect the I2C pin, is it OK?

Thanks

Jun Shen

  • 0
    TI__Mastermind 23815 points

    Hi Jun,

    What is the DC voltage in DP139's output when DP139 is not  powered up and there is a DVI display plugged?

    Are you able to measure the current in TMDS lines?

    On DP139's side you don't need 50 ohms termination resistors, those resistors will be on display side.

    I2C_EN should be tied low for DVI applications, I2C registers are disables and rise/fall times are reduced.

    Regards

  • 0 in reply to Moises Garcia
    TI__Mastermind 23815 points
    Hi Jun,

    I have reviewed schematic in email, now I understand what you meant with I2C pins disconnected.
    DP139 has an I2C buffer and I2C register for HDMI mode, since the application is for DVI, you don't need the I2C registers, but I2C buffer would be useful.
    Do they still have a connection of DDC from GPU to DVI connector? Can they see traffic on DDC?
    If not using DP139's I2C buffer, they still need pullups, check GPU requirements.
    However this wouldn't be the reason for DC voltage issue.

    Have you tried different IC or different displays?

    Regards