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TX517: Output transformer

Thomas Riedl
Prodigy 40 points
Other Parts Discussed in Thread: TX517, AFE58JD18
Hi,
We have designed an ultrasound transmit analog front end around the TI TX517 chip and we had a few questions regarding its design.
Our current design works but does not include a transformer at the output as used in the evaluation board design. We assume the transformer is used for EMI mitigation reasons? Are there any other benefits from using a transformer at the output? We were wondering what transformer you recommend there and whether we need to AC couple into the transformer to prevent shortening of the TX517.
Our goal is to play out broadband signals occupying the frequency band from 100kHz to 500kHz.
Thank you for your help.
Thomas
  • 0
    TI__Mastermind 49176 points
    Hi Thomas,

    We have received your inquiry about the transformer recommendation for TX517 and hope to have some answers back to you shortly.
  • 0
    TI__Genius 12025 points

    Hi Thomas,

    Thanks for using our TX517 transmitter.

    We will look into your questions

    and will reply to you very soon.

    Thank you very much!

    Best regards,

    Chen

  • 0 in reply to Chen Kung
    TI__Genius 12025 points

    Hi Thomas,

    There are two analog outputs (with very high voltages) from the TX517.

    One is CHA OUTA and the other is CHB OUTB.

    We use a transformer to combine OUTA and OUTB together

    to create the OUTA-OUTB output to multi-level pulses.

    You can see the explanation from our TX517 data sheet and users guide:

    also shown below:

    For example:

    Here is the plot showing:

    CHA OUTA (shown in purple color) 5-level

    CHB OUTB (shown in green color) 5-level

    OUTA-OUTB (shown in Red color) 17-level

    (Can be done by using a transformer)

    We are using DA2319 Coilcraft transformer which covers freq 50kHz-2MHz range.

    Of course if your board design already includes the same purpose like us as using a transformer to do OUTA-OUTB,

    then you don't need to use any extra transformer to do so.

    Thanks and best regards,

    Chen

  • 0 in reply to Chen Kung
    Prodigy 40 points

    I do not understand what you mean by "Of course if your board design already includes the same purpose like us as using a transformer to do OUTA-OUTB, then you don't need to use any extra transformer to do so."

    What is the benefit of the transformer? 

    I also wonder what the benefit of Diodes D1 and D2 is in your schematic above. Can I leave those out?

    Thanks,

    Thomas

  • 0 in reply to Thomas Riedl
    TI__Expert 6320 points

    Thomas,

    The TX517 can be used as a dual-channel, 5-level TX, or a single-channel 17-level TX.  To achieve 17-level, you need to use a transformer to subtract OUTB from OUTA.  For instance, OUTA=+60V, OUTB=-20V, then XFMR output is then +80V. The diodes are for damping.  when the signal drops below ABS(Vdiode), then the output at C11 is isolated from the TX517 and XFMR output.

    If this is a multi-channel SONAR type imaging application, please look at our AFE5401 and AFE58JD18, as well.

    Thanks,

    Chuck

  • 0 in reply to Chuck Smyth
    Prodigy 40 points
    Hi Chuck,

    I understand that if a transformer is used the load sees the difference OUTA-OUTB at its input.

    However, if OUTA and OUTB were directly connected to the two leads of the load, wouldn't the load also see the difference OUTA-OUTB at its input? I feel there must be another reason why a transformer is used.

    Thanks,

    Thomas
  • 0 in reply to Thomas Riedl
    TI__Genius 12025 points

    Hi Thomas,

    The advantage of using a transformer is:

    Each channel output has 5 levels with high voltages.

    You can just use one channel output with its own load resistor for that channel.

    In this case we don't need to use any transformer.

    You can use two channel OUTA and OUTB with different output signals

    and connect them to a transformer inputs to generate OUTA-OUTB signal at the end of the transformer output.

    In this case the output has 17 levels with very high voltage.

    Thanks and best regards,

    Chen

  • 0 in reply to Chen Kung
    Expert 1705 points
    Hi,
    In the plot above which shows DA2319 Coilcraft transformer, what is the value of C11? How about the values of Diodes 1 and 2?
    Thank you
  • 0 in reply to Sajad Rahmdel
    TI__Expert 4145 points
    Hi Sajad,

    The EVM BOM on Page 22 of the user guide details the values of all components on the EVM.

    Sincerely,
    Olu