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REF3430: Voltage buffer for ADC of TMS320F280049

Giovanni Principato
Prodigy 80 points
Part Number: REF3430
Other Parts Discussed in Thread: TMS320F280049, OPA320, OPA350, TLV6741

Hi, 

I'm trying to understand if in my application i need a voltage buffer to tie REF3430 with the ADC VREF of MCU TMS320F280049. 

I read in different paper that the key parameters are: I_out (drive capability of reference voltage) and Rout (reference voltage). This parameters can be compared with the ADC characteristics Input current, etc.. 

What are the other parameters to consider to understand if I should put a voltage buffer?

What kind of OPAMP can I use as a voltage buffer in this case ?

Thank you in advance!

  • 0
    TI__Mastermind 19370 points

    Hi Giovanni,

    The benefit of the output buffer is the output impedance that is typically in the mOhms and the high capacitor drive that can be larger than the 10uF that a VREF can handle.

    The datasheet recommends OPA320/OPA350. I will add the Op Amp team for more recommendations.

  • Former Member
    0 Former Member

    Hi Giovanni,

    The main benefit of adding an op amp in a buffer configuration to your ADC's reference supply is an increase in current drive capability.  This topic is described in great depth in a series of video lectures on ADCs in TI Precision Labs.  Here is a link to the first video in the series.  The second presentation specifically goes over op amps as reference buffers.

    If you're not sure whether an amplifier will be necessary, take a look at the d/s for the reference.  There should be a block diagram of the system and/or the part itself.  If the system block diagram has an amplifier after the reference, then this is a good sign you will need one.  Alternatively, if there is no buffer built into the reference part, this is also a sign.  If you are unsure, you can always ask on e2e.

    As far as how to pick an op amp, you should begin by considering a few factors.  First is "does it have the needed accuracy?"  The most important figures of merit are voltage offset and offset drift.  The better your ADC and reference, the better the op amp will have to be.  For most applications, a precision op amp with an offset of a few hundred uV or less will be used.  Better ADC -> Better Reference -> Better Op Amp  If you have a low precision application, like perhaps an 8-bit or 10-bit ADC, then you may be able to use a less accurate and less expensive device to save money (like the TLV6741).  Other factors, such as output current capability, should also be considered.  I spent some time in the precision ADC group and the most common recommendation was the OPA320, though it may not always be the best choice.

    I hope this helps you in your design.

    Regards,
    Daniel

  • Former Member
    0 Former Member in reply to Marcoo Z

    Hi Marco,

    For this type of question, you will usually get a better response from the precision amplifier team (LAMPS -> PRAMPS) since they do more of these designs.

    Regards,
    Daniel

  • 0 in reply to Former Member
    Prodigy 80 points

    Hi Daniel,

    thank you so much for your answer!

    Regards,

    Giovanni P.