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TMDS171: ON OFF operation of power

K.Hamamoto
Guru 12155 points

Part Number: TMDS171

Hi

Our customer evaluates at some abnormal condition such as ON/OFF operation of power supply (kind of temporary power down).

And they found a unknown phenomenon.

If the power OFF / ON test is repeated, an event that the TMDS signal is not output from the TMDS 171 will occur about 1/100 times.
Since there are several questions, please confirm the following question.

1) Datasheet: There is a sequence gauge in "8.3.2 Operation Timing" on page 23, but is there a regulation of ON → OFF → ON sequence? (Image as shown on the bellow)
    * For example,since the power supply voltage does not falls if it is not taken for more than a few ms from OFF to ON, there is a possibility of malfunction etc.

2) Since the TMDS signal is not output, it may be in the standby mode.
What is the condition that TMDS is not output in the state of power ON and TMDS input?

3) In order to investigate the cause mentioned above, are there any registers for reference when checking register setting?

And I have another question that is not related above question.Regarding the pull up resistor at control pin, the resistor is 65kohm as it mentioned at the datasheet.

However the cusotmer connect the pull up resistor (65kohm) from 3.3V supply rail to the control pin then the voltage of the controll pin will be 2.5V.

The min voltage of VIH is 2.6V as it defined at datasheet. The voltage of the pins is lower than the specification.

Is this correct?

Best Regards,

Koji Hamamoto

  • 0
    TI__Guru**** 192641 points
    Hamamoto-san

    Are they toggling OE signal during this power on/off test? Please check and make sure when device is powered up again, then they are properly following the section 8.3.2 Operation Timing on page 23.

    When there is no TMDS output, can they toggle OE signal and see if there is an output?

    For the 65k pullup resistor, are they seeing 2.5V on multiple control pins or just one control pin?

    Thanks
    David
  • 0 in reply to David (ASIC) Liu
    TI__Guru 60870 points
    Hi Koji,

    Yes, the 65K pullup yields the correct value for the pin. The min voltage of Vih is defined for an actively driven signal only - there is a note at the bottom of the table in the datasheet.

    Regards,
    JMMN
  • 0 in reply to David (ASIC) Liu
    Guru 12155 points
    Hi David-san,

    Thank you for your reply.
    I am asking our customer to check how they set OE pin. If I got the information, I will let you know.

    Best Regards,
    Koji Hamamoto
  • 0 in reply to JMMN
    Guru 12155 points

    Hi JMMN,

    Thank you for your reply.

    I saw the notes that you mentioned. However I do not understand what this notes means.

    (Is that the following notes what you mentioned?)

    >The min voltage of Vih is defined for an actively driven signal only 

    What is the actively signal?

    Best Regards,

    Koji Hamamoto

  • 0 in reply to K.Hamamoto
    TI__Guru 60870 points
    Hi,

    Yes, those notes are the ones I was talking about. If the application is using a passive pullup (resistor), then the Vih(min) does not apply. The Vih(min) only applies for a signal that is being driven by another device in the system (FPGA / microcontoller) .

    Please let me know if that is not clear.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Guru 12155 points
    Hi JMMN-san,

    I understood.
    So, how much is the voltage at those pin expect to be when those pin is pull up by 65kohm resistor to 3.3V supply rail?

    Best Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Guru 60870 points
    Hi,

    There is not a defined Vih (min) for those pins when a external pullup resistor is connected.

    Regards,
    JMMN