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SN74LVC2G07: Unexpected votlage level at pin 1A

Antony Lin
Genius 13480 points
Part Number: SN74LVC2G07
Other Parts Discussed in Thread: STRIKE

Hi,

We currently encounter a strange situation (unexpected voltage level) at pin1 (1A) of SN74LVC2G07.  As shown below, USB_0_1_OC_N is from another chip with open drain output in the original design, so customer implement external pull-up resistor (R1261) to P3V3_STBY.  For testing purpose, now customer disconnect USB_0_1_OC_N trace on the board so that SN74LVC2G07 pin1 is only connected to the 33ohm (R1187) and then 10kohn(R1261) to P3V3_STBY.

For such connection, we expect pin1 to be 3.3V, but found it's only 2.8V.  If we do the same thing at pin3 (2A), the voltage is 3.3V as expected.  Meanwhile, the output voltage lvel at 1Y and 2Y are normal.  Can you explain why we see 2.8V here?  Thanks!

Antony

Antony

  • 0
    TI__Mastermind 45675 points
    Hi Antony,

    I want to verify that the resistor (R1261) is actually the correct 10K value and there wasn't an error in population, can I get confirmation that someone measured this? Also are they able to measure the current at 1A to compare to 2A, that would be helpful as well.
  • 0 in reply to Dylan Hubbard
    TI__Genius 13480 points

    Hi Dylan,

    R1261 is confirmed to be 10kohm.  In parallel, the voltage level becomes 3.19V when R1261 is changed to 2.1kohm.

    Antony

  • 0 in reply to Antony Lin
    TI__Mastermind 45675 points
    Hi Antony,

    That's what I would expect when reducing the resistor size to 2.1K. Could I get measurement of the resistance of pin 1A to GND? Also are there multiple boards with the same issue?
  • 0 in reply to Dylan Hubbard
    TI__Genius 13480 points

    HI Dylan,

    The resistance of pin 1A to GND and pin2 A to GND are both 10Kohm., and the issue is found on more than one board.

    Thanks!

    Antony

  • 0 in reply to Antony Lin
    TI__Mastermind 45675 points
    Hi Antony,

    Did they measure this while the device is populated on the board? If they could remove the device and measure (if it wasn't done that way before). While they have the device off the board can they put on a device from a board they don't see this issue on? I was trying to identify if it was a possible ESD strike on pin 1A, but this seems less likely now with multiple boards having the issue. However, since I wasn't given a quantity of boards with the same issue then I could still assume it only is happening to several boards out of a large quantity making the ESD strike on the pin 1A still plausible.