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I'm having a hard time finding a regulator that fits these constraints:

  • High PSRR (>80 dB @ 0..50 kHz), low noise.
  • Vin = 5.5V, Vout = 5V, IoutMax = 200mA. Dropout voltage preferably < 200 mV.
  • Managable package size: not smaller than SOT-23-5 or similar. Larger is no problem.
  • Affordable and available through Mouser / Farnell / Digikey (MOQ <= 10).

I've found a few candidates, but none that tick all the boxes. Can anyone recommend me one?

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  • \$\begingroup\$ Would you be more specific what is your definition of high PSRR, how much do you need and at what frequency range? \$\endgroup\$
    – Justme
    Feb 5, 2020 at 17:54
  • \$\begingroup\$ Shopping questions are off topic- Go to one of the major manufacturer's websites and use the parametric search to find a regulator that meets your specs. \$\endgroup\$
    – John D
    Feb 5, 2020 at 18:20
  • \$\begingroup\$ Consider adding a filter ahead of the regulator. \$\endgroup\$ Feb 5, 2020 at 22:32
  • \$\begingroup\$ Consider improving it with a RC filter prior to the LDO. \$\endgroup\$
    – MadHatter
    Feb 6, 2020 at 0:32

2 Answers 2

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High PSRR (>80 dB @ 0..50 kHz), low noise. Vin = 5.5V, Vout = 5V, IoutMax = 200mA. Dropout voltage preferably < 200 mV.

That's a problem.

Good PSRR and regulation both depend on the LDO's pass transistor characteristics. You'll get better performance if the pass device is fast, low capacitance, high gain, etc.

All these characteristics degrade significantly when dropout voltage gets below one volt. I'll use Tim's ADP7142 as example. The datasheet has a PSRR versus dropout graph:

enter image description here

This graph is very important! It shows excellent PSRR above 80dB over a wide frequency range, with 1V headroom or more.

However, as headroom decreases, down to 500mV in your case, PSRR drops very quickly, to about 55dB and the corner frequency drops too.

That's simply a consequence of the pass transistor getting squeezed, it'll have higher capacitance, it'll be slower, etc.

I'm not going to search for a regulator, but please keep in mind if you want low dropout and high PSRR you must check PSRR is specified at at your dropout voltage. Otherwise you'll get a surprise.

Also, high PSRR up to 50k will probably require a ferrite bead and capacitor as filter.

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The ADP7142(AUJZ-5.0-R7) seems to check most of the boxes. Not the highest PSRR LDO available, but this seems to be the most affordable one while meeting the rest of the demands.

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