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SN74LVC16245A: SN74LVC16245A with floating inputs

Ami POM
Prodigy 10 points
Part Number: SN74LVC16245A

Hi

I know floating levels (HighZ) at a CMOS gate input is a dangerous problem as both FETs can be ON simultaneously, thus to create a short from Vcc to GND and burn this gate.

I would like to ask the following:

1. If the OEn (output enable) pin of the 74lvc16245ADGG device is at "1" (output at HighZ) , will it change in any matter the above danger to the chip due to floating inputs?

2. If I don't want to change the current PCB layout and had pull ups at the chip inputs, what are my other options to reduce the above risks?

3. Is the 74lvcH16245ADGG a good option to overcome the floating inputs state?

4. In case I replace current chip with the 74lvcH16245ADGG chip, does it mean I have to remove from my current design all the pull ups over the 74lvcH16245ADGG outputs?

Looking forward to hear from you

Thanks

Ami

  • 0
    TI__Guru* 96681 points

    Hi Ami,

    Ami POM said:
    1. If the OEn (output enable) pin of the 74lvc16245ADGG device is at "1" (output at HighZ) , will it change in any matter the above danger to the chip due to floating inputs?

    No - the OEn pin only disables the outputs on this device -- the inputs are still active.

    Ami POM said:
    2. If I don't want to change the current PCB layout and had pull ups at the chip inputs, what are my other options to reduce the above risks?

    If all of the inputs are pulled up to VCC, then there is no danger.

    Ami POM said:
    3. Is the 74lvcH16245ADGG a good option to overcome the floating inputs state?

    Yes, the bus-hold circuits are intended to prevent this issue.

    Ami POM said:
    4. In case I replace current chip with the 74lvcH16245ADGG chip, does it mean I have to remove from my current design all the pull ups over the 74lvcH16245ADGG outputs?

    Yes, pull-up resistors will conflict with the bus-hold circuits.

    You can choose to have the circuits pulled-up by the bus-hold circuits by always having the inputs in the high state just before the OEn pin is toggled.

  • 0 in reply to Emrys Maier
    Prodigy 10 points

    Many Thanks

    Ami