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TMDS442/TFP410 pin terminal voltage

Hidetoshi Matsunami
Expert 2750 points
Other Parts Discussed in Thread: TFP410, TMDS442

Hello Team,

I'd like to ask you about TMDS442/TFP410 pin terminal voltage.

Could you tell me the reason why my customer observed the following voltage of pin terminal for TMDS442/TFP410 in a normal operation.

  • OVS(No.32) pin for TMDS442
    • condition: Floating, observed voltage: around 1.5V
    • I suppose that I can observe the dividing V_cc however there is no resistor rating in data sheet.Therefore I'd like to know the rating of these resistor.

  • VSADJ(No.51) pin for TMDS442
    • condition: 4.64kohm Pull-Down, observed voltage: around 1.25V
    • I suppose that I can observe the GND level for VSADJ pin(because of pull-down).
  • Z11-Y14(No.53-63) pin for TMDS442
    • condition: Floating, observed voltage: around 0.53V
    • I suppose that I can observe the GND level for Z11-Y14 pin(because of circuit of datasheet).
  • TFADJ(No.19) pin for TFP410
    • condition: 510ohm Pull-Up, observed voltage: around 2.8V.
    • I suppose that I can observe the Vcc for TFADJ pin(because of pull-up).

Best Regards,

Hidetoshi Matsunami

  • 0
    TI__Mastermind 36085 points

    Hello Matsunami-san,

         I am reviewing your questions and I will have a response within 24 hours.

    Regards,

    Diego.

  • 0 in reply to Diego Cortes
    Expert 2750 points

    Hello Diego,

    I'm looking forward to hearing from you.

    Best Regards,

    Hidetoshi Matsunami

  • 0
    TI__Mastermind 36085 points

    Hello Matsunami-san,

    OVS(No.32) pin for TMDS442:

         The voltage you are measuring is mostly due the input diodes and transistors, but not the resistors you are mentioning. Remember that this is an input, which draws an approximate value of 10 uA (input capacitance= 10 pF) and must be driven by the following voltages:

    VSADJ(No.51) pin for TMDS442:

     You are correct, the measured voltage is due the pull-down resistor.

    Z11-Y14(No.53-63) pin for TMDS442

    The output stages are current mode outputs, these terminals are designed to provide an output in terms of current (not voltage) and must be terminated to VCC in order to provide a valid output (i.e. when the output is connected to the sink side). So the measured value when the output is floating is an undetermined value .

    TFADJ(No.19) pin for TFP410

    Your assumption is incorrect, since there is no internal open-circuit in this terminal. The measured value is the result of the voltage divisor generated by the pull-up resistor and the input resistance of the TFADJ terminal.

    Best regards,

    Diego.

  • 0 in reply to Diego Cortes
    Expert 2750 points

    Hello Diego,

    I'd like to ask you some additional questions.

    OVS(No.32) pin for TMDS442:

    I believe OVS pin can be floating because of the following.

    Also is there any problem if my customer observed around 1.5V at OVS pin(OVS pin is Floating)?

     

    VSADJ(No.51) pin for TMDS442:

    I believe I can observe GND level at VSADJ pin due to pull-down resistor.

    However, my customer observed 1.25 V at VSADJ pin with 4.64 kΩ pull-down.

    Is there any problem?

     

    Z11-Y14(No.53-63) pin for TMDS442:

    Would it be possible for the unused TMDS output pin to be floating?

    e.g) Both Z11 & Y11 pin is floating.

     

    TFADJ(No.19) pin for TFP410:

    >Your assumption is incorrect, since there is no internal open-circuit in this terminal. The measured value is the >result of the voltage divisor generated by the pull-up resistor and the input resistance of the TFADJ terminal.

    Could you tell me the rating of  the input resistance for the TFADJ terminal?

    Best Regards,

    Hidetoshi Matsunami

  • 0 in reply to Hidetoshi Matsunami
    Expert 2750 points

    Hello Diego,

    I'm looking forward to hearing from you.

    Best Regards,

    Hidetoshi Matsunami

  • 0 in reply to Hidetoshi Matsunami
    TI__Mastermind 36085 points

    Hello Matsunami-san,

    Here you go the feedback for your questions:

    OVS(No.32) pin for TMDS442: Yes, it could be floating and the customer don't have to worry about the 1.5V, indeed as you can see, it's about VCC/2, so its fine.

    VSADJ(No.51) pin for TMDS442: your assumtion is incorrect, due to the pull-down is in order to establish a polarization current, this means that the voltage seen on the pin is product of a voltage divisor, generated by the pull-down and the terminal impedance. 

    Z11-Y14(No.53-63) pin for TMDS442: yes it is possible, however I recommend to terminate the unused signals to VCC as it would happen with a connected sink. 

    TFADJ(No.19) pin for TFP410: Could you tell me the rating of  the input resistance for the TFADJ terminal? I need more time to review this question,

    Regards,

    Diego.

  • 0 in reply to Diego Cortes
    Expert 2750 points

    Hello Diego,

    Thank you very much for your reply.

    I understood it.

    Also I wait for your answer as follows.

    >TFADJ(No.19) pin for TFP410: Could you tell me the rating of  the input resistance for the TFADJ terminal? I need more time to >review this question,

    Best Regards,

    Hidetoshi Matsunami

  • 0 in reply to Hidetoshi Matsunami
    TI__Intellectual 1805 points

    Hi Hidetoshi,

    In TFADJ pin there will be always a voltage of 2.8V. This pin is a current sensor, and its input impedance is in the MegaOhms order.

    Regards,

    Aldo.

  • 0 in reply to Aldo Acero
    Expert 2750 points

    Hello Aldo,

    Thank you for your support.

    I understood it.

    Regards,

    Hidetoshi Matsunami