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TXB0108: Possible to connect two TXB0108 in serial ?

BERNARD FROMENT
Intellectual 270 points
Part Number: TXB0108

Hi,

I need help to know if 2 TXB0108 can be serialy connected.

I mean by serially connected when the Bx pins of the first one are connected to the Ax pins of the second one.

I explain the problem:

I use a computer board which GPIO level are translated from 1V8 to 3V3 with a first TXB0108 (And I dont have acces to these chip)

But I need to get GPIO level in 5V, so I need to convert again from 3V3 to 5V with another TXB0108.

My question is simple : Will it work ?

I must mention that I need to keep these GPIO bidirectional.

Thanks by advance

Bernard FROMENT, Engineer

  • 0
    Guru 316690 points

    Section 8.3.2 of the datasheet says that "for proper operation, the device driving the data I/Os of the TXB0108 must have drive strength of at least ±2 mA." But the TXB outputs are not designed for a DC current of more than 20 µA. It might work in the lab (because the edge accelerators have a higher drive strength for a short time), but it is not guaranteed at all.

    And the TXB should not try to drive capacitive loads above 70 pF. With long traces, cables, or connectors, you are likely to exceed this limit.

    And the TXB cannot be used with normal pull-up or pull-down resistors.

    If possible, use a direction-controlled translator.

  • 0 in reply to Clemens Ladisch
    Intellectual 270 points

    Hi Clemens,

    OK to use a 245 series but the direction is not "automatic" like in the TXB series.

    So, no solution to keep the automatic bidirectional function ?

    Regards

    Bernard FROMENT

  • 0 in reply to BERNARD FROMENT
    Guru 316690 points

    Any automatic-bidirectional translator is required to have weak outputs so that other devices can override them. The consequences of that mean that the TXB should be used only as a last resort, and in many circumstances cannot be used. If you want to omit the DIR signals just for convenience, don't.