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PCM5102A: Can I use op-amp with PCM5102A?

Lukas Sidlauskas
Prodigy 120 points
Part Number: PCM5102A
Other Parts Discussed in Thread: OPA1622, OPA1678

Hello,

Is it possible to use op-amp with PCM5102A? In my application the load is much lower than 10k, so as a result I have much lower Vrms than it's defined in the datasheet (2.1V). So maybe it's possible to use op-amp or should I use a different DAC chip for this application then?

  • 0
    TI__Guru 52683 points

    Hi Lukas,

    Of course you can use an op amp buffer on the output. The selection of the op amp will be dependent on the load. If you are planning on driving speakers or a headphone output, then you can take a look at our TPAxxxx devices. If you are driving a intermediate load or high impedance headphones, you can consider the OPA1622.

    Thanks,
    Paul

  • 0 in reply to Paul_Frost
    Prodigy 120 points
    Hi Paul,

    Thanks for the answer. I'll be driving car's head unit through it's CD changer input, so not sure what load is it. Maybe there is a standard for this?
  • 0 in reply to Lukas Sidlauskas
    TI__Guru 52683 points

    I am not aware of a CD input standard, but you might check the head unit manual.  I would expect it to be pretty high impedance, so the PCM5102A would be able to drive it directly.  You mentioned that your output is attenuated, how much? If you look at the output of the PCM without plugging it into the head unit, is it what your expect? 

    Thanks,

    Paul 

  • 0 in reply to Paul_Frost
    Prodigy 120 points
    yes, PCM5102A is able to drive it directly, but the output is attenuated compared to other head unit sources like CD or FM radio, so the amplifier should work much harder and as a result at higher volumes I can even hear audio amplifier hum noise at the silent places of the soundtrack and so on..
  • 0 in reply to Lukas Sidlauskas
    TI__Guru 52683 points
    Well the OPA1622 is a very capable amplifier and I suspect it can drive the load (~100mA output drive capability, I believe). That might be a good start.
  • 0 in reply to Paul_Frost
    Prodigy 120 points

    Could you please provide a reference design? Because everything I found on your web page is for differential outputs only.

  • 0 in reply to Lukas Sidlauskas
    TI__Guru 52683 points

    Hi Lukas,

    Here is a diagram I put together.  Note that you should use thin film resistors and C0G/NP0 ceramics for the passive components.  The amplifier could be a device like the OPA1622 if you are expecting a high current load, or a device like the the OPA1678 if you just need a simple buffer.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 120 points

    Many thanks for this diagram! I find it very helpful! Btw, can this be directly connected to OUTL and OUTR of PCM5102A? Or I should still leave 470R resistor and 2.2nF cap at the output of PCM5102A before op-amp? Another question is what would be the easiest way to power this op-amp?

  • 0 in reply to Lukas Sidlauskas
    TI__Mastermind 46290 points
    Lukas,

    Paul's suggestion has essentially replaced the recommended first-order R/C filter with a second-order low-pass amplifier circuit. They are not both necessary.

    "Easiest" way to power the amplifier is a sort of ambiguous question to answer as this has some system-level dependencies. In general LDOs are recommended to augment PSRR along with the use of decoupling capacitors. The OPA1678 datasheet includes some basic suggestions and all the relevant curves and figures for selecting a suitable power supply.