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Driving issue with TXB0106

Ali Sayyah
Prodigy 10 points
Other Parts Discussed in Thread: LMX2433, TXB0106

I am using TXB0106 for translating the 3.3V data and clock lines from FPGA  to 1.8V level data and clock ports of the LMX2433 PLL synthesizer. The clock and data pulses are not clean and I see multiple transients at each pulse when I zoom it using a storage oscilloscope. When I increase iput lcurrent evel from the FPGA ports (by increasing the internal capacitance from 10 pF to 70pF max), the transients go away and the clock pulses become clean but with high overshoot spikes. Is this normal with TXB0106 voltage translator?? do we need to boost the input current for each line (say using a transistor)? 

Thanks

Ali Sayyah 

  • 0
    TI__Genius 9085 points

    Hi Ali,

    The TXB devices require a strong enough driving current to overpower the internal 4kOhm buffer resistance, so it makes sense increasing the drive current could improve the performance of our device. Below I've included a link to an application note that goes into more detail. If the load the TXB sees is too heavy (> 70pF), the rising and falling edges are too slow, or the driver is not strong enough, you can get signal distortion.

    I'm not sure what the internal capacitance refers to. Is this what the FPGA expects to drive? Do you have a copy of the waveforms I could see?

    http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=scea043