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TS3DV642: The LVDS display is blinking

Wenting Wu
Intellectual 2455 points
Part Number: TS3DV642


Hello Expert,

Could you help to check the the schematic of TS3DV642 done by my customer?

There is an issue that the network interface goes from down to up state, the network interface initializes, and then links up. LVDS flashes when ip is acquired.
software in uboot first to pull the EN pin low, then control SEL2 switch pin, finally kernel to pull the EN pin high, SEL1 is high by default. (Switch to SWITH-B side)

 

Best regards,

Wenting

 

TS3DV642 issue.jpg

 

 

  • 0
    TI__Expert 7305 points

    Hi Wenting,

    The only concern I have with the schematic right now is that the unused I/O pins are left floating. These should be terminated to ground to help reduce noise.

    Could you please clarify the issue that the customer is seeing with an oscope picture that shows what the customer expects vs what the customer is seeing on the mux? The LVDS blinking is external to the mux, so it is not clear to me what the issue with the mux is.

    Best,
    Katy

  • 0 in reply to Katy West
    TI__Intellectual 2455 points

    Hello Katy,

    Could you help to check the connection of unused float I/O pin?

    Best regards,

    WENTING,

  • 0 in reply to Wenting Wu
    TI__Intellectual 2455 points

    Hello Katy,

    Please see the oscope picture. 

    When the customer  execute "udhcpc -i eth2", the customer can observe waveforms at the LVDS port and the LVDS screen will flicker as shown. 

    Best regards,

    Wenting

  • 0 in reply to Wenting Wu
    TI__Expert 7305 points

    Hi Wenting,

    That looks good! Just make sure to match the resistance to that of the system's termination (typically 50ohms, but not always).

    Best,
    Katy

  • 0 in reply to Wenting Wu
    TI__Expert 7305 points

    Hi Wenting,

    Thanks for sharing the oscope shot. Could you please specify what pin of the mux this is, as well as any other input conditions (VCC, voltage on SEL pins, etc)?

    Best,
    Katy

  • 0 in reply to Katy West
    TI__Intellectual 2455 points

    Hello Katy,

    At udhcpc -i ETH2, EN, SEL1, SEL2 are high, There are no fluctuations, including VDD_3V3 power supplies.
    The waveform below is on the DOP_A side.

    Best regards,

    Wenting

  • 0 in reply to Wenting Wu
    TI__Expert 7305 points

    Hi Wenting, 

    I would not expect a spike on the DO+A side when all other inputs to the mux are stable. In the original post, it said "finally kernel to pull the EN pin high" - does that mean that this spike above occurs when EN changes from low to high? It would be very helpful to see a scope shot with 4 probes at the same time - on EN (or SEL - choose the one that is being changed), DO+A, DO+B, DO+

    Best,
    Katy

  • 0 in reply to Katy West
    TI__Intellectual 2455 points

    Hello Katy, 

    The EN keeps high and the EN pin connect to 3.3V directly. 

    Best regards,

    Wenting

  • 0 in reply to Wenting Wu
    TI__Expert 7305 points

    Hi Wenting,

    Could you please share a scope shot with more than just DOP+A? From what you have stated, I would not expect any fluctuation in the voltage on DOP+A, so it would be beneficial to see the whole picture - in case there is any unexpected behaviour on other pins. Ideally, the scope shot(s) would have VCC, DOP+, DOP+A, DOP+B, SEL1, SEL2 & EN. 

    Best,
    Katy