• State Resolved
  • Locked Locked
  • Replies 9 replies
  • Answers 3 answers
  • Subscribers 34 subscribers
  • Views 595 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

AM5718: HDMI interface to TPD12S016

AM5718: HDMI interface to TPD12S016 (2)

Marco Caldari
Intellectual 290 points
Part Number: AM5718
Other Parts Discussed in Thread: TPD12S016

Hi everybody,

in our custom board with AM5718 we use the TPD12S016 with VCCA at 1.8V.

We discovered that we are driving the LS_OE input with a +3.3V signal connected to GPIO6_28 of AM5718.

The LS_OE input is referenced to VCCA (+1.8V) so we would like to know if this condition can damage the pin or if it can be tolerated; the absolute maximum rating on this pin is 4.0V.

Many thanks in advance for your support.

Marco

  • 0
    TI__Mastermind 33331 points
    Marco,

    I am going to have to look into this a bit further. The answer will depend on the level shifter architecture. The concern will be forward biased diodes and latchup.

    I will get back to you early next week with and answer.
  • 0 in reply to Chuck Branch
    Intellectual 290 points

    Hi Chuck,

    thank you for your reply and for your support on this issue.

    In the current implementation GPIO6_28 on AM5718 is set as an output pin driving "strong" +3.3V and 0V levels with a minimum drive strength of 6mA.

    To reduce the amount of current flowing into LS_OE pin of TPD12S016 we are considering to drive the logic '1' configuring GPIO6_28 as an input pin with internal pull-up.

    The AM5718 specification for a dual voltage LVCMOS pin in 3.3V mode reports an input current from 10uA to 290uA when the internal weak pull-up is enabled.

    We modified our SW to try this new setup and the LS_OE is driven at about +3.13V; this level still exceedes the recommended specification but the maximum current is limited to 290uA.

    Considering the LS_OE input pin specification and the level shifter architecture do you think that this new configuration can be considered more reliable?

    Please let us know your opinion.

    Marco

  • 0 in reply to Marco Caldari
    TI__Mastermind 33331 points

    Marco,

    TI cannot guarantee reliability of the device for input voltages greater than VCCA+ 0.5V on the LS_OE pin, so unfortunately I cannot recommend this solution.

    Here is the section of the ABS_MAX table that shows this requirement:

    You will need to limit the voltage of this signal to closer to 2.3V MAX.  Do you have room to put a resistive divider on the PCB?  This signal does not rapidly toggle, so this might be a workable solution.

    Regards,

    Chuck

  • 0 in reply to Chuck Branch
    Intellectual 290 points
    Hi Chuck,
    regarding LS_OE we considered it as an input (as it is reported in the datasheet) so we considered +4.0V as a maximum rating.

    Furthermore in the same page note 1 states that: "The input and output voltage ratings may be exceeded if the input and output clamp-current ratings are observed."

    Our new configuration limits the maximum current to 290uA, is this value low enough to accept the +3.3V voltage level on LS_OE?

    Please let us know your opinion.

    Marco
  • 0 in reply to Marco Caldari
    TI__Mastermind 33331 points
    Marco,

    You are correct, it appears to be an error in the datasheet that LS_OE is listed in the output specification range.

    The clamp current ranges are specified for inputs that are lower than 0V, so they will not apply in this case.

    Based on your control of the current, I don't see any issue with the part being damaged by the higher voltage, but TI cannot guarantee that the device will meet specification because this voltage exceeds the recommended operating voltage of VCCA.
  • 0 in reply to Chuck Branch
    Intellectual 290 points
    Hi Chuck,
    during the measurements with the new configuration we noted that the voltage on LS_OE was around +3.3V; in case of a clamp diode inside the TPD12S018 we should have measured something like +2.3V or 2.4V, is this correct?

    The specification for the clamp current are given only for voltages below 0V, is it possible that only the clamp diode from the input to GND is present?

    Please let us know your opinion.

    Marco
  • 0 in reply to Marco Caldari
    TI__Mastermind 33331 points
    Marco,

    The datasheet calls out a clamp voltage minimum of 6V, so your measurement is consistent with the specification.

    Again, TI cannot guarantee datasheet performance for parameters greater than the values called out as normal operating conditions. The part is guaranteed not to be damaged by conditions called out in the ABSMAX section of the speciication.

    Regards,
    Chuck
  • 0 in reply to Chuck Branch
    Intellectual 290 points

    Hi Chuck,

    many thanks for your reply and for your support.

    Kind regards,

    Marco

  • 0 in reply to Marco Caldari
    TI__Mastermind 33331 points
    My pleasure.

    I am going to go ahead and close this thread. I appreciate it if you can click the customer thinks resolved button for me.