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SN74AUC34: Part Help

Avi Loschak
Prodigy 90 points
Part Number: SN74AUC34

Hi,

I am trying to use this SN74AUC34 device as a fanout buffer for my ADC SCLK. I had a few questions, though, regarding on how to set it up, as the datasheet doesn't give too much information.

1. How should I bypass Vcc? 

2. What should I do with unused outputs? I am only using 4 of the 6.

3. For the unused inputs, it says to either pull them up to Vcc or pull them down to GND. Is one more preferable than the other?

4. Should I leave the EPAD floating or should I ground it?

Thank you very much.

  • 0
    TI__Guru* 96862 points

    Hello Avi,

    1. How should I bypass Vcc? 

    We recommend using a 0.1uF capacitor placed as close as possible to the device. Since this device has a thermal pad, that can be tied to ground, then the capacitor can easily be connected between Vcc and the thermal pad.

    2. What should I do with unused outputs? I am only using 4 of the 6.

    Unused outputs can be left floating.

    3. For the unused inputs, it says to either pull them up to Vcc or pull them down to GND. Is one more preferable than the other?

    As mentioned above, since the thermal pad is already connected to ground, it would be easiest to just route a trace to the thermal pad to ground the unused inputs.

    4. Should I leave the EPAD floating or should I ground it?

    It is recommended (but not required) to connect the exposed thermal pad to ground. This will help with thermal conduction as well as making routing easier.

  • 0 in reply to Emrys Maier
    Prodigy 90 points

    Hi Emrys,

    Thank you for your replies. Regarding number 3, however, it seems to me that you're suggesting to directly pull them down to GND. It seems from the note on the datasheet though that it is supposed to be tied down with a resistor and links to another document where there is an entire section dedicated to calculating that pull-down resistor value. What do you suggest I do?

    Again, thank you for your time.

  • 0 in reply to Avi Loschak
    TI__Guru* 96862 points
    A pull-down is only required if you plan to use the channel, but also want it to be pulled down to ground when not in use. A direct connection is the best for unused channels.
  • 0 in reply to Emrys Maier
    Prodigy 90 points

    Ah, okay, wonderful. Thank you very much!