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Original question:

re: SN74CBTD3306PWR - cross talk between input and output.

SN74CBTD3306C: threshold voltage for OE# pin

Kay Chen53
Expert 2225 points
Part Number: SN74CBTD3306C
Other Parts Discussed in Thread: SN74CBTD3306

Hi there:

Our customer would like to check the detail parameter of SN74CBTD3306C

such as OE# pin's threshold voltage range.

  • 0
    TI__Expert 3900 points

    Hi Kay,

    Please refer to the datasheet of the SN74CBTD3306C for details of all parameters.

    The OE# pin threshold voltage range is defined by the VIH and VIL specs in the datasheet. Please see that attached image the I captured from the recommended operation conditions table.

  • 0 in reply to Dakotah
    Expert 2225 points

    Hi Dakotah:

    thanks for the information

    update application from customer

    The reason of checking Vth about SN74CBTD3306:

    an spike voltage (under 0V ) happened in 1A/2A  pin, what's the accept voltage range for this pin will not trigger the 1B/2B (not happened with  SN74CBTD3306C) ? 

    schematic

    waveform (not SN74CBTD3306) 

  • 0 in reply to Kay Chen53
    TI__Expert 3900 points

    Hi Kay,

    I am a bit confused by your question.

    If I am interpreting it correctly the customer is looking into two devices: the SN74CBTD3306 and SN74CBTD3306C.

    If the custumer system has a negative voltage spike on the signal path, the correct part to use is the SN74CBTD3306C. This device supports -2V undershoot operation. Please reference the following application note for more on the undershoot protection of the "-C" devices. 

  • 0 in reply to Dakotah
    Expert 2225 points

    Hi Dakotah:

    Thanks again, correct the P/N into: SN74CBTD3306

    Also would like to double check the Vth voltage of it. 

  • 0 in reply to Kay Chen53
    TI__Expert 3900 points

    Kay,

    Please reference recommended operating conditions table for VIH and VIL threshold specs.

    Please rememeber - if you do not use the SN74CBTD3306C you will be outside of the operating conditions if your system has a negative voltage on the signal path (up to -2V).

  • 0 in reply to Dakotah
    Prodigy 20 points
    Dear Dakotah,

    Thank you for your reply.

    I obtain the information the SN74CBTD3306C supports -2V undershoot operation on signal path, but how much supports the SN74CBTD3306?
    In other words, the gate voltage of the n-channel pass transistors are at ground potential, but a negative voltage on either I/O port with a magnitude greater than the NMOS VT will cause the switch to conduct and no longer isolate the buses.
    - SN74CBTD3306C: VT is 2V.
    - SN74CBTD3306: VT is ?

    Best Regards,
    Eric Hung
  • 0 in reply to Eric Hung12
    TI__Expert 3900 points

    Eric,

    The SN74CBTD3306 can support voltages as low as GND on the signal path to be within the recommended operating range. 

    If you need the negative undershoot protection the SN74CBTD3306C is the correct part. 

  • 0 in reply to Dakotah
    Prodigy 20 points
    Dear Dakotah,

    Thank you for your information.
    But I don't think there is not any design tolerance on the signal path. (only as low as GND)

    I still would like to understand the ability of SN74CBTD3306 negative undershoot protection.
    Could you give me a actual design VT value of SN74CBTD3306?
    example:
    - SN74CBTD3306 VT="0V", so SN74CBTD3306 negative undershoot protection up to "0V"
    - SN74CBTD3306 VT="0.01V", so SN74CBTD3306 negative undershoot protection up to "-0.01V"
    - SN74CBTD3306 VT="1V", so SN74CBTD3306 negative undershoot protection up to "-1V"

    Best Regards,
    Eric Hung
  • 0 in reply to Eric Hung12
    TI__Expert 3900 points
    Hi Eric,

    While margin is implemented into our designs, for reliability reasons we only guarantee within the limits mentioned in the datasheet. While some devices may be able to support negative undershoot with SN74CBTD3306 we do not guarantee this performance.

    If the need for negative undershoot is required for your system, please use the SN74CBTD3306C to stay within the operating conditions of the device.