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TXS0102: Max capacitive load when using for push-pull?

Benjamin Lonske
Prodigy 155 points
Part Number: TXS0102
Other Parts Discussed in Thread: SN74AXC2T245, SN74LVC2G66

Can the TXS0102 drive a 2nF capacitive load when operating push-pull as a UART level shifter? 115.2kbps, 3.3V on both sides.

Also, is it okay if VCCA is slightly higher than VCCB (say 0.1V higher) if our 3.3V regulators on both sides are not set exactly the same?

Thank you,

Ben

  • 0
    Guru 276980 points

    With 3.3 V on both sides, you are not level shifting. What is the purpose of the TXS in your circuit?

    The edge accelerators cannot handle more than 70 pF. After the edge accelerator has timed out, the 2 nF is charged only through the 10 kΩ pull-up resistors, with an RC time constant of 20 µs.

    Differences smaller than about 0.5 V do not matter.

    For two unidirectional signals, it might be a better idea to use a buffered device like the SN74AXC2T245.

  • 0 in reply to Clemens Ladisch
    Prodigy 155 points

    Good to know! 20usec won't work at that data rate.

    I'm using a level shifter for the VCC Isolation feature, to prevent back-powering. Is there a better way?

  • 0 in reply to Benjamin Lonske
    Guru 276980 points

    The SN74AXC2T245 has an /OE input. Can you control this?

    If your other devices have enough drive strength for the 2 nF load, you can use a passive switch like the SN74LVC2G66.