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LP5907 vs. TPS7A4901: PSRR - Which is better for post-regulation of a switching supply?

Nick56152
Intellectual 545 points
Other Parts Discussed in Thread: LP5907

I was wondering which of these LDOs is more suitable for post-regulation of a switching supply (a buck converter switching at around 1.125 MHz).


The LP5907 datasheet does not contain PSRR plots/graphs up to 1 MHz (unlike the TPS7A4901 datasheet) so I am unsure as to which one would reject switching noise more effectively.

Any ideas?

Many thanks.

  • 0
    TI__Guru 55940 points

    Hi Nick,

    For either of these devices the PSRR will be dominated by the output capacitor selected at the frequency you are interested in.  In PSRR plots, the "hump" out around the 1MHz range is the affect of the output capacitor.  Right before and after the output capacitor you will note that the curve is decreasing roughly linearly so you can estimate what the LP5907 curve will look like at the higher frequencies.  

    Very Respectfully,

    Ryan