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TPS7A84A: high PSRR at 900KHz

Intellectual 2575 points

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Part Number: TPS7A84A

I am currently looking at my options for filtering out some 900KHz supply ripple using an LDO. The application requires that the LDO be able to source >= 2.2A (>3A preferred for derating), and be able to output 5.0V (external resistors OK).

 

I found the TPS7A84A and TPS7A85A in your catalog and they seems OK, but using the parallel capacitor combination suggested in 8.1.1.7 it seems I only get ~20dB of power supply rejection at 900KHz on either part.

 

Can I use the capacitor values I choose and the  boost circuit described in 8.1.3.1 of both datasheets (http://www.ti.com/lit/ds/symlink/tps7a84a.pdf & http://www.ti.com/lit/ds/symlink/tps7a85a.pdf) to steer the PSRR transfer function to have more rejection at 900KHz? Do you have and application notes / reference designs about how to do this?  Or should I look for other high current LDOs with wider bandwidth?

 

 

 

  • Hi Michael, 

    I understand you would like to filter 900KHz noise and the PSRR listed at this frequency is only 20dB. The built-in PSRR boost circuit in TPS7A85A is creating a peak between 200kHz and 1MHz as shown. The limitation with this kind of boost is that the peaking frequency cannot be accurately set and the peak will vary between 200KHz and 1MHz. 

    We currently are developing the next-gen of TPS7A84/5A and based on some of the test data, the PSRR near 900KHz should be able to improve to around 40dB. Samples of TPS7A52/53/54 will be available by the end of the year. Will this be something you would be considering with?

    Regards, 
    Jason Song

    Please click the "Resolved" link at the bottom of this post if I have answered your question.

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