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SN65LVDS93A: Vcc have 1.6V and 2.56V on Pin D26 when without VCC

Fandy
Expert 2285 points
Part Number: SN65LVDS93A

Hello

Please refer to below SCH, IOVCC,VCC,PLLVCC,LVDSVCC all connect together to VDD_3.3V net，but My customer find VDD_3.3V pin have 1.6V voltage when just provide RGB signal,ENABLE,DCLK,HS,VS, actually no add external 3.3V power supply,and on D26 PIN voltage level is 2.56V. so how and why VDD_3.3V have voltage when wihout add 3.3V power. is it flow backward from other pins?

  • 0
    TI__Mastermind 35130 points
    Hi Fandy,

    I don't believe power flows backwards from other pins. Your customer says they see 1.6V on the VDD_3.3V net. Where exactly does the power for this net come from? Is it controlled by their processor?

    Regards,
    I.K.
  • 0 in reply to Ikechukwu Anyiam
    Expert 2285 points

    Hi I.K. Anyiam

    The VDD_3.3V comes from Buck IC ,its EN pin was controlled by MCU.

    Disconnect the wire between VDD_3.3V on Buck side and SN65LVDS93A side , provides the RGB,DE(pin30),SYNC signal, disabled the Buck IC, the voltage on buck output is 0V,but on SN65LVDS93A VDD_3.3V net also have 1.7V, and the DE(pin30) voltage level also becomes unstable. the waveform of DE and VDD_3.3V shows below

  • 0 in reply to Fandy
    TI__Mastermind 35130 points
    Hi Fandy,

    Understood. Actually, providing input signals to the input pins with no VDD is not a valid configuration. You can reference the Absolute Maximum Ratings table in the datasheet.

    The "voltage at any input terminal" must be within the range of -0.5 to IOVCC+ 0.5 V. When you have VDD_3.3 (and conversely, IOVCC) =0 V but are still providing signals to the inputs, you are violating the specification. In this case, there is probably some ESD protection circuitry that is becoming biased and causing the behavior your customer sees.

    Regards,
    I.K.