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LSF0102: could I use LSF as a I2C Buffer?

Aviad Savitzki
Prodigy 30 points
Part Number: LSF0102
Other Parts Discussed in Thread: TCA9800

Hello, I have some problem with the LSF0102DQE, while I'm using him as a I2C shifter from 1.2v to 3.3v.

I have a designed circuit :

Before my testing all the Rpu were 5K and the signal(after the shifter) were looked as : 

After some "playing" with my RpaA and RpaB the best signal looks :

but still I can't see a prefect I2C bus, my HAC/NAC always changes not going back to 0 geting back to 0.44v , some bits during the switching between high to low not going back to 0v as well .

My I2C freq is not more than 400KHz, as in the spec (on 3.3v of I2c protocol )  the Rpu need to be between 320-2.9k, with this spec I tested the board but it was looking more like the first pic.

Am I doing something wrong ? what do i miss, or the LSF can't be a Buffer for I2C bus ?

  • 0
    Guru 317630 points

    The LSF is not a buffer but a passive switch. The pull-up resistors on both sides act in parallel.

    It is not necessary for rising edges to be very straight; the pull-up resistors should only by strong enough that the voltage reliably reaches VCC. 2.2 kΩ on both sides should work fine.

    If you want a buffer, use something like the TCA9800/1/2/3.