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Original question:

LSF0108: LSF0108 translation 1.8V/3.3V@100MHz

LSF0108: SDIO 50Mhz

Allan Fan
Expert 7220 points
Part Number: LSF0108
Other Parts Discussed in Thread: TXS0206A,

Tool/software:

Hi expert,

Customer is looking for a level shift solution 1.8V <> 3.3V for SDIO with 50Mhz clock rate. They used to use TXS but failed and pass with TXB. What they learnt it might because of the internal pullup of TXS cause SDIO_CLK don't need pullup but data and cmd do.

But what I see the DS of TXB, it looks weird to me TXB can only support up to 30Mhz. (TXS can only support up to 35Mhz for 1.8V <> 3.3V). 

We discussed about TXS0206A but the pitch is too small and need extra cost for pcb assembly so the plan was rejected. 

Now they consider more flexible LSF0108 with external pullups which is also p2p with TXB. However, I see the thread "LSF0108 translation 1.8V/3.3V@100MHz", we don't recommend LSF for SDIO.

I'm confused that the reason we put the figure 1 in LSF0108 DS is the use case is still acceptable or not recommended at all?

 Customer prefer to consolidate multi-chips into single solution for 6ch SDIO CLK, CMD, and DATAn(4bit). Would it be doable and could you please advise a proper solution?

p.s. there is actually another need for UART and GPIO level shift. So it's preferable for customer if LSF0108 can also be used for easier BOM control. 

Regards,

Allan

  • 0
    Guru 318700 points

    The LSF is a passive switch; when translating up, the rising edge is generated by the pull-up resistor. (This can be seen in the figure above, where the red waveform is rather slow.)

    To reach 50 MHz, you need to use very strong pull-up resistors. This means that both your SDIO devices must be able to sink the current through these resistors, or else their VOL becomes too high. I do not know the drive strength of these devices.

    As far as I can see, the TXS0206A is the only solution for fast SDIO translation.

    The LSF could be used for UART and GPIO, if the pull-up resistors are OK. In general, TXU translators would be a better choice.