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Overcurrent Protection for IO

Yaron Rahamim1
Prodigy 170 points
Other Parts Discussed in Thread: INA303

Hi,

I'm designing a board with multiple IOs (probably from a CPLD) which will be connected to external test boards. Each IO will be set as input or output and will work at 10MHz.

I have to design a protection circuit for each IO, in case the user will connect an IO directly to GND or to VCC (fault connection) by mistake.

The requirement is to limit the current to 8mA, so in case of such a fault connection the IO will be disconnected immediately - so there will be no damage to the external board.

Should I use a concept of: current sense amplifier which its output is connected to the OE of a bi-directional buffer?

Any suggestion how to design such a circuit for a single IO - simple and cheap?

Thanks,

Yaron.

  • 0
    Guru 316690 points

    What are the electrical characteristics of the inputs on the external boards? How much drive strength do you need for normal operation?

    After an output has been disabled, the current is zero. So I guess you want a latched error state? And would it be allowed to disable multiple outputs in that state?

    Do the outputs need to be disabled, or would it be possible to limit the curent by reducing the output voltage?

  • 0 in reply to Clemens Ladisch
    Prodigy 170 points

    Hi, Clemens,

    The device should support many external boards, both old and new, so I don't have all of their information. I do know that the voltage of the IOs is 1.8/2.5/3.3/5V. No normal current was defined, but the request is to limit the drive current to 8mA.

    In case of a faulty IO, it must be disable but no indication is required. Only the faulty IO must be disabled but all the other outputs should work as usual. I'm looking for a solution per a single IO.

    The output just need to be disabled.

  • 0 in reply to Yaron Rahamim1
    Guru 316690 points

    If you want to disable the output, then you need to sense the current (in both directions), and generate a signal when the current is too low or too high. The smallest solution is a bidirectional current-sense amplifier with integrated comparators, such as the INA303.

  • 0 in reply to Clemens Ladisch
    Prodigy 170 points

    Clemens, many thanks.