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LSF0108: LSF0108 layout placement ?

Jimmy Huang
Prodigy 40 points
Part Number: LSF0108
Other Parts Discussed in Thread: TXU0304

Tool/software:

Hi Ti pals,

We use LSF0108 for SPI signals level translator from 3.3V to 1.8V. 

Topology is shown below:

FPGA SPI (3.3V) on A board  -> board to board connector (BTB CONN) -> LSF0108 on B board -> SPI Flash (1.8V) on B board.

The routing length is about 11 inch between  BTB CONN and SPI flash.

We wolud like to know the LSF0108 need to be placed close to BTB CONN or SPI flash side when layout placement?   

Thanks,

Jimmy Huang

  • 0
    TI__Mastermind 39986 points

    Hi Jimmy,

    For SPI translation, the TXU0304 (4-ch) would be most suitable as the direction of the signal flow per channel is optimized for this interface. The LSF0108 has open drain outputs on A/B side, meaning that the external RC from the external pullups and Cload will determine the max achievable speed. Since SPI contains MISO/ MOSI lines, the output will be at both sides of the device so even if the device is placed closed to BTB CONN or SPI flash, the SI on opposite side of the device will be degraded.

    If 8-ch is needed, 2x TXU0304 or a direction controlled translator like the AXC8T245/ AVC8T245/ LXC8T245 can be realized for improved robustness and SI due to its buffering outputs. 

    Regards,

    Jack