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LMH6554: Design Inquiry

Abhishek Manoj
Intellectual 345 points
Part Number: LMH6554
Other Parts Discussed in Thread: THS3217, THS3491

Tool/software:

Hi Team,

In my board, I required a analog fanout buffer IC 1:4, 1:8 or 1:12 configuration.

My DAC output is passed through an output amplifier to get +/-1.85V output voltage range to the signals.

Those signals then need to fed into a fanout buffer as i want to convert the single DAC output to 12 outputs that has to be fed into a mixer IC.

 LMH6554 is only single, I can't use single channel if it 1:4 also i can cascade an provide 12 output signals.

Can you please suggest a fanout buffer for my requirement.

Regards,

Abhishek

  • 0
    TI__Mastermind 23299 points

    Hello Abhishek,

    Do you need these fanout signals to be differential or single-ended?  LMH6554 is a fully-differential amplifier which drives two output pins as a differential pair with OUT+ and OUT- being 180 degrees out of phase.

    How are these 4/8/12 fanout signals being loaded?  

    Let me know how I can better assist you here.  What is your gain and bandwidth needs for this fanout circuit?  Are you looking for true buffer behavior, with a gain of 1?

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Intellectual 345 points

    Hi Alec,

    The fanout signals need to be single-ended.  The below block diagram shows my requirement.

    The signal need to fed to the mixer IC is 134.4kHz sine wave. From a single DAC output, i want to give input to 12 different mixer ICs. For that i asked for a analog fanout buffer IC so that i can buffer the single input to 12 inputs.

    It is will very good if I'm getting a 1:12 so that i can use a single IC for my need. If not i can cascade 1:4 or 1:6 buffer for my requirement.

    Regards,
    Abhishek

  • 0 in reply to Abhishek Manoj
    Intellectual 345 points

    Hi Alec,

    Please provide an update on the above query.

    Regards,

    Abhishek

  • 0 in reply to Abhishek Manoj
    Intellectual 345 points

    Hi Alec, 

    Our requirement block diagram is shared below.

    Please suggest a fanout buffer as per our requirement.

    Regards,

    Abhishek

  • 0 in reply to Abhishek Manoj
    TI__Mastermind 23299 points

    Hello Abhishek,

    We may need to discuss an alternative device architecture: FDAs are fully-differential amplifiers which do work best when providing differential output.  Your system needs as a DAC buffer to drive the DAC output are to construct an output buffer & a fanout buffer amplifier; these two parts would be differential input to single-ended output and for the fanout single-ended input to single-ended output.  For the fanout circuit, the signal at the output remains single-ended even though it is brought to multiple copies of the same output signal.

    For an example of an older device we have for driving DAC outputs, you can see the THS3217.  We also have high performance current-feedback amplifiers, such as THS3491, which can drive a current output of a DAC into various loads or multiple channels (high output current on the THS3491).

    Is my understanding of your system needs correct?  For LMH6554 you would be taking a single input signal and generating two output signals, with the signals being 180 degrees out of phase from each other and each output at 1/2 the amplitude of the differential signal.  This does not appear to satisfy any block of your signal chain diagram.

    Let me work on a proposal which may align better with your system goals.  Thank you Abhishek.

    Best,

    Alec