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LSF0204: Questions for LSF0204

Max Guan
Intellectual 1350 points
Part Number: LSF0204

Hi team,

Some questions from my customer evaluating LSF0204 in the design as I2C level shifter (also isolation).

1. As the EN follow the logic of VrefA, will there be leakage from An to Bn if we only pull-high Vrefn (and leave VrefB 0V)?

2. If customer also plans to use LSF0204 as the GPIO level shifter, where the GPIOs are push-pull outputs, do we need the external pull-high voltage rail any more? Or we need pull-high on the Bn side only when An side is push pull GPIO output?

Thanks

Max 

  • 0
    TI__Guru* 96591 points

    Hi Max,

    I would recommend to first go through these videos for a detailed explanation of the LSF faimly of translators. Note that LSF0204 includes the 200kohm resistor and has a different enable pin configuration than the LSF01xx that are more prominently shown in the videos, but otherwise the functionality is the same.

    Understanding the LSF family of bidirectional, multi-voltage level translators | TI.com Training Series

    Max Guan said:
    1. As the EN follow the logic of VrefA, will there be leakage from An to Bn if we only pull-high Vrefn (and leave VrefB 0V)?

    I would expect there to be no current across any of the channels (An to Bn or Bn to An) with VrefB = 0V. This will bring the bias point for the devices to 0V (see videos above) and force all the channels into a high-impedance state.

    Max Guan said:
    2. If customer also plans to use LSF0204 as the GPIO level shifter, where the GPIOs are push-pull outputs, do we need the external pull-high voltage rail any more? Or we need pull-high on the Bn side only when An side is push pull GPIO output?

    Pull-up resistors are required for up-translation, only at the output of the device. Please see this video for an explanation of how this works: 

    Up Translation with the LSF Family | TI.com Video