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TXB0108 low output problem

Tom Hobson
Prodigy 110 points
Other Parts Discussed in Thread: TXB0108, ADS1299

Hello!

I'm using a TXB0108 in conjunction with an ADS1299 and an AVR. The problem that I'm having is that my output voltages for time-varying signals are low or non-existent. The set up is as follows:

Vcca = 3.3V

Vccb = 5V

OE = Vcca = 3.3V

My 5Vpp clock signal just doesn't show up on the corresponding output pin, for instance. It just hovers around 1.5V or so. However, 5V DC will be properly translated down to 3.3V.

I don't think that it's a pull up/down thing on the inputs to the ADS1299. I double checked this by trying with an unused pair of pins and encountered the same problem.

thanks!

  • 0
    Prodigy 110 points

    Here's a bit of an update:

    I can see the output signal on the 3.3V side toggling, but the difference between the two states is very small - around 25 mV - and it's all centred around 1.5V as I stated before.

  • 0 in reply to Tom Hobson
    Prodigy 20 points

    I have a similar problem found in circuit and retested out of the complete circuit:

    VccA = 2.6V (coming from a lab power supply)

    VccB = 3.9V (coming from a LIPO)

    Using a quality multimeter (input impedance of 1Mohm), I have the following measures:

    Input=2.6V, Output=1.9V

    Input=GND, Output=1.7V or 0V (random?)

    When adding on the Output a 200kOhm resistance to GND, it seems to work better:

    Input=2.6V, Output=3.8V

    Input=GND, Output=0V

    What is happening? Before using this chip in production, we must understand why a load is necessary and which one is the best. Thanks a lot!


    Denis

  • 0 in reply to Denis Alaime
    TI__Expert 6430 points

    Hi Denis,

    Dose output PCB trace is longer than 10cm? Could you provide some schematic ?

    Thanks

    Wei

  • 0 in reply to Wei Lang
    Prodigy 20 points

    Hi Wei,

    thank you for your reply. I look at the length of the tracks and come to you with a schematic.
    thank you,
    Denis.