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LSF0102: Cascading using output of LSF0102 as Vref and Enable of 4 LSF0102

Stuart Smith1
Prodigy 150 points
Part Number: LSF0102
Other Parts Discussed in Thread: SN74AUP1T34

Hello

I would like to use the output of one LSF0102 as the Vref/Enable of four other LSF0102 devices. The device driving the initial input (CONF_EN_1V8) is an Intel MAXII CPLD with up to 2mA drive capability at 1.8V. Given that the LSF0102 should only be sinking 17uA (through a 200kOhm resistor), this should be enough to drive the Vref and Enable pins of four other LS0102 devices? Is my thinking correct or is there something that I am overlooking with regard to the switching transistor in the LSF0102. Any help would be appreciated. Thanks in advance.

I have placed (an untidy, my apologies) diagram below for reference. The highlights show the intended application.

  • 0
    TI__Guru* 97046 points
    Hi Stuart,
    In your circuit, there's no way for CONF_EN_3V3 to draw power from V330C. LSF is a passive translator and does not provide current of its own. If you'd like to learn more about how the LSF operates, I would highly recommend watching the short video series here: training.ti.com/LogicMinute

    I would recommend switching out your U121 LSF0102 for an SN74AUP1T34. The SN74AUP1T34 will provide an active output at 3.3V to drive the supplies of all the LSF devices down-stream, and the input will be able to switch on and off all the devices simultaneously.

    Also, I don't see any pull-up resistors on the other LSF devices -- you will need those for them to operate. Again, refer to the video series above.
  • 0 in reply to Emrys Maier
    Prodigy 150 points

    Thank you for your feedback. I found my mistake. I consider this topic closed.