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LSF0102 (Level shifter) pin assign & layout

Victor Park
Intellectual 1240 points
Other Parts Discussed in Thread: LSF0102

Hi,

 

I have two questions for LSF0102 or general voltage tanslator in MDIO interface condition.

  1. For unused input and output, which pin assign(Gnd or open) is better and why?
  2. In datasheets, there is guideline and I've captured it below. I'd like to know why it is better layout design for voltage translator.

    • Place LSF close to high voltage side.

Regards,

Victor Park

  • 0
    TI__Guru* 96681 points

    Hi Victor,

    We have an excellent application note on the LSF series of translators here that you might like to read.

    To answer your questions directly:

    1.  It is recommended to tie at least one port on each unused channel to ground to avoid leaving a pin floating (either the A or B side is fine).  The reason for this is to avoid having a pin on the device with an unknown voltage level.  Only one side of the unused channel needs to be tied to ground, but both can be because the LSF does not produce current.

    2. Since the LSF is a passive FET based translator, when the low side input goes HIGH, the internal FET turns off and the high side output is pulled high by the pullup resistor.  The speed at which this happens is tied directly to the output RC values.  Shorter traces mean less impedance and a faster switching time.