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reference design for THS4120

Michelle Ferment
Intellectual 1440 points
Other Parts Discussed in Thread: THS4120, THS4130, THS4521, PCM4204, OPA2377

Customer looking to THS4120 (or THS4130) for a new design. It will take its input from a hydrophone and output to a AD1974 ADC... I have the THS4120 Datasheet... I was wondering if you can point me to a reference design or other that would provide some guidance (or things to watch out for, etc...). I need to use a single power supply ~ probably 3.3VDC, but maybe 5 VDC.

thanks

  • 0
    TI__Expert 5400 points

    Hi Michelle,

    I would recommend considering using the THS4521 over the THS4120, which are pin compatible.  It offers superior performance in most respects (lower noise, better distortion performance, and includes Ground in the Common Mode input range) and it also allows single supply operation from +2.5V to +5.5V, in the event that only 5V is available, as you mention.

    The THS4521 datasheet offers a thorough demonstration of using the device as an audio ADC driver (page 31), with a device similar to the AD1974, the PCM4204.  Note that the AD1974 requires a common mode input of 1.5V as opposed to 2.5V in the example, so its Vref pin will need to remain connected to VOCM on the THS4521.

    Let me know if the customer cannot substitute the THS4521 with the THS4120.

  • 0 in reply to Bart Stiller
    Prodigy 10 points

    Hello Bart:

    Thanks for the reply.  Do you think a simple replacement of the THS4120 with the THS4521 would do (I believe Michelle has provided you with ckt I'm using)?  Or, should the input device (in this case a hydrophone) voltage not be offset by VOCM of the ADC (which it currently is with OPA2377 Op Amps).  It seems to me that maybe I should not be offsetting the input by VOCM because the feedback from ADC will already do this... correct?  I believe this is the major difference between the design on the front page of the TSH4521 datasheet, and the one that I have provided.  Please reply.  Thanks.

     

  • 0 in reply to Dean Pieretti
    TI__Expert 5400 points

    Hi Dean,

    The output of the hydrophone should not need to be level shifted.  That would be necessary with the THS4120, since its minimum common-mode input voltage is 0.35V, but since the common-mode input range of the THS4521 includes ground this isn't necessary.

    I haven't been provided with the schematic yet, but would like to take a look to try to anticipate any issues.  If you have a typical output waveform of the hydrophone that would also be useful.  I will ask Michelle to arrange this outside of this public forum --