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SN74CB3T3384: 3V to 5V Level conversion

Remya Nellikkal
Prodigy 70 points
Part Number: SN74CB3T3384
Other Parts Discussed in Thread: TXB0108, , LSF0108, SN74LVC8T245

Hi Sir,

We are desperately looking for 3V to 5V level conversion device with 8 inputs/outputs.

SN74CB3T3384PWR part looks fine for the above application (3V power supply input, VCC).

We need bidirectional level conversion and one side device can accept a max. voltage up-to 3.15V after that it may get damaged. The other side device operates in 5V and hence we need 3V to 5V level conversion.

TXB0108 is a good solution for us, but it is dual supply and have a Tpd of 4ns when operating in 3V as VCCA. But we cannot compromise on the same. \

So please support us to resolve this issue that we can go with part SN74CB3T3384PWR.

Thanks & Regards,

Remya

  • 0
    TI__Mastermind 45430 points
    Remya,

    The SN74CBT3T3384 device partly relies on the internal NFET Vt to clamp the signal to Vcc. This is how placing a 5V signal on one side of the switch will only be 3V on the other. In order to have the opposite be true you will need to have pull up to 5 V on one side of the switch because the if 3V is placed on one side of the switch only 3 V would show up on the other side.

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    Prodigy 70 points

    Hi Adam,

    Thanks for the mail. I understood that the out put is clamped to 3V device, but please let me know the tolerance of the signal output level (3V+/- ) so that i can check that this voltage level will not damage the 3V device input pin.

    5V side of my device (When as input) needs a VIHmin of 2.4V & VILmax of 0.6V and 3V output will satisfy this condition. Please confirm.

    So in the above case pull up to 5V is not required. Please correct me.

    When 5V side is output, then VOHmin is 4.6V and VOLmax is 0.4V which SN74CB3T3384 can accept correctly. \

    Thanks & Regards,

    Remya

  • 0 in reply to Remya Nellikkal
    TI__Mastermind 45430 points

    Remya,

    I understood that the out put is clamped to 3V device, but please let me know the tolerance of the signal output level (3V+/- ) so that i can check that this voltage level will not damage the 3V device input pin.

    I'm not sure of the tolerance of the output because it isn't stated in the datasheet. Since this is an older device this data might not be available but I can try and do some digging through some archives next week.

    The input and output voltage relationship is shown in the plots below with Vcc = 5 V

    5V side of my device (When as input) needs a VIHmin of 2.4V & VILmax of 0.6V and 3V output will satisfy this condition. Please confirm.

    As you can see above with Vcc = 3 V placing 3V on the input will result in a little less than 3 V on the output.

    So in the above case pull up to 5V is not required. Please correct me.

    You will not need a pull up if you Vih min is 2.4 V because the output voltage will be above 2.4 V

    When 5V side is output, then VOHmin is 4.6V and VOLmax is 0.4V which SN74CB3T3384 can accept correctly.

    Yes, the SN74CB3T3384 can accept signals 0 to 5.5 V.

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    TI__Mastermind 45430 points
    Remya,

    I wasn't able to find any old data. Do you have any additional questions to help you with your project?

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    Prodigy 70 points

    Hi Adam,

    Thanks for the information.

    Can i make use of the part LSF0108 for my level conversion requirement?

    Do i need to use pull-up resistors both the sides of the converter?

    Since i need a bi-directional level conversion, any additional direction control mechanism to be implemented, please clarify.

    (Note: My outputs are push pull both the ends of the level converters.)

    Thanks,

    Remya

  • 0 in reply to Remya Nellikkal
    TI__Mastermind 44765 points

    Hi Remya,

    The LSF0108 can work for this application, but if you don't need auto bidirection (doesn't seem like you do here) you could also use a device like the SN74LVC8T245.

    If you want to use the LSF device, feel free to watch these training videos to help get you started:

    https://training.ti.com/introduction-voltage-level-translation-lsf-family