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txb0104 latching high?

stewart fletcher
Prodigy 20 points
Other Parts Discussed in Thread: TXB0104

I am attempting to level shift a digital input to a GPIO on an ARM micro.

I am manually simulating the digital input by using a push -button connected between  VccB and B4 and a 56k pull down resistor.

when I push the button both A4 and B4 go high and remain high.  It appears that  A4  goes high, latches high and pushes back towards the button.

I have tried a pull down resistor on the GPIO side with no luck.

what am I missing?

ta

  • 0
    TI__Expert 4705 points

    Hi,

    Can you show me your schematic? or show the diagram of the connection for the TXb0104? then I can be clear for your design.

    Also, I need to know is it appears power on or all power supply is OK, you just put the button to add the pull down resistor? for the A side, any pull up resistor added or any driver drive it?

    I need to know your clear applicaiton and what is your target and what is the status of the A side.

    BR

    Junjie

  • 0 in reply to Junjie Mai
    Prodigy 20 points

    in this iteration the port "digital" is input only. it level shifts a 5v pulse from external electronics for the 3.3v tolerant gpios.  A TXB0104 was used to allow bidirectional interfaces in the future. The other ports where used because they were convenient, but are not critical.

    the button is temporary - purely for software development.

    On pressing the button, A and B side both go high and stay high. A holds at approximately 3.3v and B holds at approx 5v.  There is a wire between jp9 and p9. if this is pulled both A and B remain high.  A pulldown resistor on side A will pull both A and B low when it is connected, but once it is connected it has no more effect. Attempting to drive A low from the micro causes the micro to become unstable and the port to oscillate.

    I can supply trace snapshots tommorow

    ta

    stu

  • 0 in reply to stewart fletcher
    Mastermind 7395 points

    Simulate your digital signal with two pushbuttons, one to VCC and one to GND.

  • 0 in reply to Avi Chami1
    TI__Expert 4705 points

    Hi,

    Yes, if you want to simulate this, please add two buttons, one to Vcc to simulate high, one to GND to simulation "Low".

    this TXB familiy part needs the driver has a little stronger drive capability. Your 56Kohms is a little higer can not raise the original high to low.  any further questions, please let me know.

    BR
    Junjie