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SN74LV1T125: SN74LV1T125DBVR - CMOS and TTL interface

LM
Prodigy 215 points
Part Number: SN74LV1T125
Other Parts Discussed in Thread: SN74AHCT1G125, , TXB0102, TXB0104

Hi there,

I would to use this device as an interface between a 3.3V CMOS device and a 5V TTL device. 

The communication between the devices is UART (unidirectional).

Is this suitable? Do I need PUs and/or PDs?


Kind regard,

Laura

  • +1
    Guru 243220 points

    Yes, this will work. You would need PUs/PDs only if you need a signal line to have a defined voltage when it is not actively driven.

    For these voltages, the cheaper SN74AHCT1G125 would work just as well.

  • 0
    TI__Mastermind 23373 points

    Hey Laura,

    The SN74LV1T125, along with Clemens recommendation of the SN74AHCT1G125 would work, but it would be an unnecessary multi chip solution. Take a look at the TXB0104 if you're doing 4 pin UART and TXB0102 for 2 pin to condense this down to a single chip solution. 
    You typically won't need pullup/pulldowns on UART lines since they're push pull, however they can be used to keep the lines from floating during power up if that's a concern but otherwise, these aren't necessary and would depend on your system and use case. If they are need however, the resistor values must be over 50k when using the TXB devices. 

    Thanks,
    Rami 

  • 0
    Prodigy 215 points

    The SN74LV1T125 is designed with current-drive capability of 8 mA to reduce line reflections.
    And the maximum current is 25 mA. Can it drive at 25 mA?

  • 0 in reply to LM
    TI__Mastermind 23373 points

    The device can drive 25mA but it's not recommended. This is just the absolute max before seeing permanent damage to the device. We can't guarantee the specs in the datasheet when working with conditions between absolute max and recommended.
    The recommended operating conditions table specifies a 8mA max output current for a 5.0V supply.