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SN74AVC4T774: Logic forum

Raj Vasanth
Prodigy 110 points

Part Number: SN74AVC4T774

Hi,

We use a SN74AVC4T774PWR Level Translator circuit as shown in the image below and found the OUTPUT to be not working.

Before proceeding, the directions were checked and verified.

We found MISO line(Pin 5) to be not working and injected a square wave from a FG while checking Output on the B3(Pin 12).

There were no change in the Logic states at the output while input was at 1khz frequency with 3.2Vpp.

So I probed at the Pin 5 where the frequncy was injected and found the waveform to be like this.

Note :- FG probe and Scope Probe were kept at Pin 5 at the same time.

Below is the actual waveform directly from the FG to the Scope.

Note :- No intervention of circuit is involved here. Direct connection from FG to the Scope.

Below image shows the Set parameters from FG.

We see the Vpp getting reduced than the actual set Vpp. There seems to be an offset in the voltage levels as Well. 

This could be the reason why we dont see any state in the OUTPUT. It always stay at HIGH Logic.

Regards,

Raj

  • 0
    TI__Mastermind 47735 points

    Hi Raj,

    So there is nothing connected to that pin other than the FG and probe? Is your scope set up for the right termination? Have you tried to swap in another device to see if the current device could be somehow damaged?

  • 0 in reply to Dylan Hubbard
    Prodigy 110 points

    Yes the probe is set at 10x and the chip was replaced,anyhow the issue persist. 

    I believe the set parameters on Signal generator is corrcect and verified with a scope.

    Does two buffers on End to End devices for SPI affect the functionality?.

    Thank You

    Raj.

  • 0 in reply to Raj Vasanth
    TI__Guru* 97666 points

    Hi Raj,

    Every logic device we ship is tested prior to packaging -- the device worked fine when it left TI. It's possible that it has been damaged due to poor handling (ESD strikes) or over-voltage conditions, but that's relatively rare. It probably still works fine and it's just a question of fixing the test setup.

    10x is not a termination type, it is a multiplier for the signal input of the scope probe.

    If you can provide a complete diagram of all connections including each type of connector and wire used, I might be able to help.