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TXB0108: Device not passing higher frequency clock signals

Mike Doyle
Prodigy 40 points

Part Number: TXB0108
Other Parts Discussed in Thread: SN74LVC2T45

Hi...I am using the TXB0108 as a level shifter in a communications system design where clock and data are passed through the device. I am not using it in a bidirectional mode. My input side is running at 1.8V and the output at 5V. At clock rates below about 45MHz, the device works fine passing the clock and data signals through. However, when the clock signal begins to approach 50Mhz the level shifter stops passing it through. The output just sits low. The psuedo random data is getting though fine at this rate but the clock does not. I believe the devices is specified up to 60MHz with these supply voltages. Any ideas on why this is happening? Thanks...Mike

  • 0
    Guru 325330 points

    The TXB is specified up to 60 Mbps. A single cycle of a square wave has two pulses, high and low, so this is the same as 30 Mhz.

    For unidirectional signals, a direction-controlled translator like the SN74LVC2T45 would be faster and more robust.

  • 0
    Prodigy 40 points

    Hello Clemens and thank you for your reply. Yes, I intend to design the part out in favor of a unidirectional part when I make a few other changes to the board. I would still like to know why this issue is happening if anyone has seen it before. Thank you!

  • 0
    Prodigy 40 points

    Hello again Clemens...I believe I misinterpreted both the data sheet and your reply. You are 100% correct. I am violating the maximum data rate with that clock signal. Thank you for your reply!