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TXU0101-Q1: The output signal is distorted when the frequency of the input signal is ~50MHz

Chunhua Ni
Prodigy 80 points
Part Number: TXU0101-Q1
Other Parts Discussed in Thread: SN74AXC4T774, SN74AUC1G17, SN74AUC1G125-EP, SN74AXC8T245

Hello TI Experts,

I am using TXU0101-Q1 to translate a 3.3V single-end signals to 1.8V, below is the schematic for your reference.

 

The McBSP_SCLK is a clock signal whose frequency is ~50MHz and duty cycle is 50%. I used the osc to measure the signals at postion 1 and position 2, respectively. Please see the below image. CH 1 is the signal @position 1, and CH2 is @position 2.

As you can see, the output of TXU0101-Q1 at position 2 is distorted if the freqency of the input is ~50MHz. It is always logical High. In the TXU0101-Q1 datasheet, the max data rate can be up to 200 Mbps when the device translates a signal from 3.3 V to 5.0 V. I am wondering the performance of this chip does not meet the requirement in my application, because when I reduced the frequency to ~10MHz, my system worked well.

Questions:

  1. The data rate in my application is ~50Mbps? What is the definition of the data rate and how to calcuate it?
  2. I reviewed the FAQ, do I have to choose another level shifter with higher data rate, like SN74AXC4T774 (310Mbps)?

Thanks.

  • 0
    Guru 259910 points

    This is not a 50 MHz signal because it is not a symmetric square wave. The length of a low pulse is only 5 ns, which corresponds to 200 Mbps (= 100 MHz).

    The TXU supports 200 Mbps only with a 5 V output. At 1.8 V, the speed is less than half (see section 6.10).

    The fastest low-voltage logic family is AUC. There is no AUC translator, but for translating down, you can also use a buffer with overvoltage-tolerant input, e.g., SN74AUC1G17. There is no automotive AUC device; the only buffer with better qualification is the military SN74AUC1G125-EP.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 25560 points

    Hi Chunhua, 

    In addition to Clemens' feedback, please note that the AXC can also support 3.3V to 1.8V translation up to 50MHz, as I have verified 1.8V<->3.3V translation for up to 160MHz in the past using the AXC EVM and would further recommend also verifying with the EVM per the system/loading requirements, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Clemens Ladisch
    Prodigy 80 points

    Hello Chemens,

    Thanks for your feedback. Please help confirm whether my understanding is correct.

    • SN74AUC1G17 is powered to a 1.8v power.
    • The chip accepts the +3.3V overvoltage signal and outputs a +1.8V signal?

    Awaiting your further comments.

  • 0 in reply to Michael Ikwuyum
    Prodigy 80 points

    Hello Michael,

    Today I did one more testing by having TXU0101-Q1 as a 1.8V->3.3V translator, when the frequency of the input signal went to ~50MHz, the performance of translator degraded and the output signal distorted also.

    I am thinking about using SN74AXC8T245 to replace TXU0101-Q1 to achieve higher data rate. Does it work?

  • +1 in reply to Chunhua Ni
    TI__Mastermind 25560 points

    Hi Chunhua, 

    Yes, this will work as the AXC family is specified for higher data rates, thanks.

    Best Regards,

    Michael.