• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 29 subscribers
  • Views 418 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OPA1641: Recommended TI part for +/-15V power supply

Francisco Salomon1
Prodigy 40 points
Part Number: OPA1641
Other Parts Discussed in Thread: TPS65130, TPS7A39

Hi, I'm developing a circuit for guitar including an OPA1641 as pre-amp, and 2 buffer stages. My design will use +/-15V, generated from +9V. In terms of power for those stages, the requirements are not defined yet, but they will be minimum.     

Is there any application note available for this kind of audio use-case? Any part/design you can recommend?

Many thanks!

  • 0
    TI__Intellectual 795 points

    Hi Francisco, 

    For starters, please take a look at the Analog Engineer's Circuit Cookbook: Amplifiers. Non-inverting microphone pre-amplifier circuit (page 269) and TIA microphone amplifier circuit (page 274) might be of interest, in addition to the basic buffer stage (page 5).  

    https://www.ti.com/seclit/sl/slyy137a/slyy137a.pdf

    Both audio circuits feature low power amplifiers, but they can be modified to include a higher supply amplifier if needed.

    Please let me know if you have further questions. 

    Regards,
    Vladimir

  • 0 in reply to Vladimir Ilic
    Prodigy 40 points

    Hi Vladimir, 

    Thanks, for your quick answer.

    The handbook is really useful! For this case though, I'm more in the split-voltage power supply design, let's say a switching DC/DC converter, in step-up mode, from +9V to +15V, and getting -15V  with a couple of diodes in reverse, from the converter output. Or maybe something similar to http://www.ti.com/product/TPS65130 (not that one, but similar), but I don't know what option would be better... 

    Since stability and low noise are important, I thought the audio forum would be a good starting point to get a suggestion for parts and circuit design.

    Any idea?

    Thanks,

    Francisco

  • 0 in reply to Francisco Salomon1
    TI__Intellectual 795 points

    Hi Francisco, 

    I'm sorry for the delay. The following guidance is the courtesy of Luis Chioye. 

    First off, the DC-DC converter will have a switching supply noise of approximately ~2mVpp at approximately 1.25-MHz (per TPS65130 datasheet). Since the PSRR of OPA1641 is only ~15-dB at ~1.25MHz, this supply noise on the supply would propagate into the audio signal.  For example, if we assume the ripple is 2mVpp at 1.25MHz, this translates to 2 mvpp/(20*log(15)) ~80uVpp at the output of the amplifier. Therefore it's important to clean up the supply to avoid the unwanted noise on the amplifier output. 

    There are several methods to filter the ripple including solutions implementing passive LC filters and power filters. However, one possible (and simple) solution that provides low noise and good DC stability is to select a low dropout regulator (LDO) with high supply ripple rejection over an extended frequency range. For instance, the TPS7A39 dual Positive and Negative LDO offers high PSRR over a wide frequency range (above 1.25-MHz) and very low output noise. One solution is to set the DC-DC converter to a voltage above the +/-15V supply (for example +/-16V) and use the TPS7A39 dual LDO to filter the noise of the supplies. The power management applications team may have other suggestions as well.

    Below is one publication that discusses the effect of the DC-DC converter noise on amplifiers and ADCs as a function of their PSRR spec. The applications note below discusses using linear regulators with high supply ripple rejection over an extended frequency range to filter DC-DC converter noise.

    https://www.planetanalog.com/signal-chain-basics-114-estimate-the-effect-of-dc-dc-supply-ripple-on-a-sar-adc-acquisition-system/

    http://www.ti.com/lit/an/slyt202/slyt202.pdf

    Please take a look at these, and let me know if you have further questions. 

    Regards,
    Vladimir