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SN74LVCH16T245: SN74LVCH16T245DGGR – Unexpected low resistance between VCCA and VCCB

Andi Mei
Prodigy 20 points
Part Number: SN74LVCH16T245

Tool/software:

Hi TI team,

I’m using the SN74LVCH16T245DGGR in a level-shifting application with the following configuration:

  • VCCA = 1.8V

  • VCCB = 3.3V

However, I’ve observed an unusual issue:

  • When I apply 3.3V to VCCB, the VCCA rail rises immediately to 3.3V, even when I’m supplying 1.8V or leaving it unconnected.

  • I measured the resistance between VCCA and VCCB (before soldering the ICs), and it’s consistently less than 2 ohms.

  • This behavior occurs on 6 different ICs, all using ICs from the same batch.

  • The top marking on the IC is: “65A1DCK” (package: TSSOP-48).

From the datasheet, VCCA and VCCB are supposed to be independent, so I would not expect this kind of interaction.

Could you please help clarify:

  1. Whether this resistance is expected or normal for this part?

  2. If this behavior might be due to internal protection features, or possibly ESD structures?

  3. Whether the “65A1DCK” marking corresponds to an official TI lot?

I’d appreciate your insights before proceeding further with hardware debugging.

Thank you in advance!

Best regards,
[Andi Mei]

  • 0
    TI__Mastermind 21720 points

    Hello Andi,

    Was this part purchased on ti.com or by a 3rd party vendor? Could you share the label it came in?

    I am not able to find this part when using the Part Marking Lookup tool. The packaging information page in the datasheet does not list "65A1DCK" as the part marking for SN74LVCH16T245DGGR.

    Regards,

    Josh

  • 0 in reply to Joshua Salinas
    Prodigy 20 points

    Hi Joshua Salinas,

    Thanks for the clarification.

    I’ve just checked again, and the IC has a two-line marking:
    - Top: 65A1DCK
    - Bottom: LVCH16T245

    The part was taken from our company’s inventory and has been in storage for a long time. Unfortunately, I do not have any traceability or original label/reel information, so I understand that TI cannot verify the authenticity in this case.

    That said, I’d appreciate it if you could help clarify:
    - Is it normal for VCCA and VCCB to show <2 ohms resistance before soldering?
    - Is there any known internal path that could cause VCCA to rise to 3.3V when only VCCB is powered?

    Thanks again for your support.

  • 0 in reply to Andi Mei
    Guru 316380 points

    "LVCH16T245" is the correct marking. "65" might indicate May 2016 or 2006.

    In any case, VCCA and VCCB should be isolated from each other. How many chips did you test in total? Do those six chips have something in common? The most likely cause is overvoltage, e.g., ESD damage due to improper handling.

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    Thanks for the confirmation.

    We’ve tested 6 chips so far from the same internal inventory batch. All of them show <2 ohm resistance between VCCA and VCCB, and all show the same behavior where VCCA is pulled up to 3.3V if VCCB is powered.

    Given that they’ve been in storage for years and their handling history is unclear, ESD damage is a very likely possibility.

    We’ll plan to replace them with known good parts from authorized sources moving forward.

    Thanks again for your help and clarification.

  • 0 in reply to Andi Mei
    TI__Mastermind 21720 points

    Hello Andi,

    No problem! Let us know if you have additional questions.

    Regards,

    Josh