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LSF0204D: Switching Characteristics (3.3V <--> 5V) of LSF0204D

Prahaladh S
Prodigy 50 points
Part Number: LSF0204D
Other Parts Discussed in Thread: TXU0104, TXV0106

Tool/software:

Hi,

Greetings...

We are planning to use LSF0204D in our application to translate a push-pull interface from 3.3V to 5V & vice versa. In the datasheet, related to the switching characteristics, I have checked that for level translation between 3.3V & 5V and vice versa, the propagation delay isn't available.

I would like to know the propagation delay (H-L & L-H) while translating from 3.3V to 5V & vice versa. Also, kindly let me know the propagation delay for the tri state as well... (Z-L, L-Z, Z-H & H-Z).

Thanks in advance.

Best Regards,

Prahaladh S

  • 0
    TI__Mastermind 23411 points

    Hey Prahaladh,

    Unfortunately, we do not have the data for the specific condition you are looking for. However, note the LSF translates voltages using a passFET architecture with no buffering circuitry (thus no added delays). The Tpd/ Tpz times is dependent on the external RC components surrounding the device. For faster rise times, stronger pullups may be used at the cost of increased power consumption and higher VOL. 

    You can refer to this set videos for more info: https://training.ti.com/introduction-voltage-level-translation-lsf-family?cu=1134826

    If your application requires tight timing margins, you may see fixed direction translators (i.e TXV0106, TXU0104) that provide buffering specifiying these switching specs. 

    Regards,

    Jack 

  • 0 in reply to Jack Guan
    Prodigy 50 points

    Hi Jack,

    Thank you for your response. I'll go through the videos and get back to you for further queries.

    Best Regards,

    Prahaladh S

  • 0 in reply to Prahaladh S
    Prodigy 50 points

    Hi Jack,

    Our application is push-pull type with 4 channels. For push pull configuration , I believe that the pull-up resistors aren't required for both up & down level translations.

    In the training series, I have seen that pull ups are required for up translation even for a push pull configuration. Kindly clarify.

    Best Regards,

    Prahaladh S

  • 0 in reply to Prahaladh S
    Guru 271840 points

    Inputs that are driven by push/pull outputs do not need pull-up resistors. But you should add pull-up resistors at all outputs.

  • 0 in reply to Clemens Ladisch
    Prodigy 50 points

    Hi Clemens,

    Thank you for your response. 

    We are using this part for bidirectional level translation. So, I believe that the pull up resistors are required for all the channels with high voltage level (Up translation).

    Example:

    We are using this for level translation from 5V to 3.3V and vice versa. So, my understanding is to add pull ups for all the channels where 5V output is expected.

    Kindly clarify.

    Best Regards,

    Prahaladh S

  • 0 in reply to Prahaladh S
    Guru 271840 points

    You should add pull-up resistors to all LSF pins that can be used as outputs. Pull-ups are required for up translation, but even for down translation, they make the output signal more robust.

  • 0 in reply to Clemens Ladisch
    Prodigy 35 points

    Dear Clemens, 

    Thank you for your response.

    I would like to know whether adding pull-up to the channel with up translation would drive the line even if the translator is disabled.

    To achieve lesser rise time, we are planning to use a pull up of 680 ohms but I feel that this would drive the lines even if the translator is disabled.

    Kindly provide your comments on the same.

    Best Regards,

    Ravichandran C

  • 0 in reply to Ravichandran C
    Guru 271840 points

    Yes; a pull-up is active as long as the power supply that it is connected to is active.