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TPS7A49: Questions about specific audio LDO

Briquel Florian
Intellectual 280 points
Part Number: TPS7A49
Other Parts Discussed in Thread: TPS7A30, TPS7A47, TPS7A39, PGA2311

Hi,

I'm looking for specific LDO for audio application.

My need:

Regulate a 34V voltage rail to 30V 60mA achieving very low noise

Regulate a 24V voltage rail to 5V 20mA very low noise for PGA23xx component

Regulate a -12V voltage rail to -5V 20mA very low noise for PGA23xx component

I think using the TPS7A49 and TPS7A30 as low noise LDO, is there parts even best especially about psrr ?

I also need a very slow rise time for my 30V voltage rail, about few seconds, says 5 seconds for exemple, is there any issue using a 4.7µF capacitor (with a 10nF in //) as Cnr/ss pin of TPS7A49 device? A such value will give me a soft start about few seconds? How will be the psrr with such a value?

Thanks for support

Florian

  • 0
    TI__Guru 55940 points
    Hi Florian,

    TPS7A49 and TPS7A30 are good choices for this application. You may also want to consider TPS7A47 for the low noise performance that it offers.

    While placing a 4.7 uF on the NR/SS pin will theoretically work it is important to note that we have not tested this LDO with such a high Cnr/ss. It is also important to note that Cnr/ss must be fully discharged before the LDO is enabled or the output of the LDO will jump to a gained version of the residual voltage at the Cnr/ss pin before continuing to startup from that point.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    TI__Mastermind 49960 points

    Hi Florian,

    You may also want to have a look at the TPS7A39

    This combines the TPS7A49 and the TPS7A30 and adds start up tracking.

    Regards,

  • 0 in reply to JCHK
    Intellectual 280 points

    Hi JCHK,

    Thanks to show me the double, I didn't identify it. A smart alternative indeed, I will look on it. At first look seems to be a little bit more noisy and low pssr than single version A49 + A30, but don't know today if this can have an impact of final thd+n performance of the amp.

    Hi Ryan,

    Thanks for informations, indeed the A47 seems to be the top competitor, a litlle bit overskill about current capacity for a single PGA2311 but results are here, I think I will just benchmark A47/A49 on the prototype to see if there is an impact on thd+n performace of amplifier. I will also test big caps value on ss pin, and maybe I have to add a fast discharger.

    Final device is an audio power amp based on pure analog circuitery (A class on a SRPP mosfet configuration) and controled by digital brain.

    Thanks for help!

    Regards,

    Florian

  • 0 in reply to Briquel Florian
    Guru 140200 points
    Hi Florian,

    if your Class A amplifier has a good PSRR, the power supply noise might not be an issue. This is usually the case if you have constant current sources as load of the differential input stage.

    Kai
  • 0 in reply to kai klaas69
    Intellectual 280 points

    Hi Kai,

    Indeed, I have a current source as load of the diff input stage. The ldo are intented to be used for digital volume control (with a pga2311), before the diff input stage. Here I need very good psrr for ldo in order to minimise the noise before input stage.

    Regards,

    Florian Briquel

  • 0 in reply to Briquel Florian
    TI__Expert 3910 points

    Florian,

    If you haven't had the opportunity already, I would also recommend take a look at our Reference Designs Search Page, where you can search for Reference Designs given a Part Number, Power Design Parameters, etc - and find Reference Designs such as:


    Note: this reference design uses TPS7A49 + TPS7A30 and includes Test Results


    Note: this reference design uses a DC-DC solution, and comes with an Application Note: Small High-Efficiency Split-Rail Supply for Portable Audio Applications