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LSF0108: 1.8V to 1.8V application

Jeff YANG
Mastermind 9075 points

Part Number: LSF0108

Hi,

We have a level shifting requirement.

The host-side SMB_CLK and SMB_DAT signals will dynamically switch between 3.3V and 1.8V, while the other signals on the B-side will remain at 3.3V.

We are uncertain whether the LSF0108 supports 1.8V to 1.8V translation.

Additionally, since the pull-up resistors on the B-side are fixed on the host side, the level shifter must not have integrated pull-up resistors. 

The LSF0108 suitable for this design? Or do you have better suggestion?

Thanks!

Jeff

  • 0
    TI__Guru 60011 points

    Hi Jeff,

    The LSF translators will support switch configuration where VREFA= VREFB voltage as well as level shifting operation in the same device. Figure 9-4 of the datasheet showcases a multi-voltage translation application where this setup can be copied similarly:

    Regards,

    Jack

  • 0 in reply to Jack Guan
    Mastermind 9075 points

    Hi Jack,

    I found P10 "10 Power Supply Recommendations" mentioned Vref_B MIN needs Vref_A + 0.8V.

    Is it still do not impact VREFA= VREFB design? Why this spec mentioned this? Thanks!

    Jeff

  • +1 in reply to Jeff YANG
    TI__Guru 60011 points

    Hi Jeff,

    The table is applicable for levels shifting applications where VREFA ≠ VREFB, in which the VREFB > VREFA + 0.8V rule is applicable. This is to help ensure that there is sufficient threshold voltage to ensure proper function of the internal FET to be in cutoff/ linear region of operation. 

    In the figure I have shared above, it is still possible to have the switch configuration of some signals where VA= VB, while other channels are level shifting 1.8V to 3.3V:

    Regards,

    Jack