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Boost converter PTN04050C is used to generate 5.3V from a 3.7V Li battery in a battery powered device. The 5.3V will be used to generate 3.3v (using LDO) for microcontrollers and +- 15v & 5v for ADCs, DACs and opamps.

Question: How much ripple voltage can be allowed to exist in the circuit? The boost conv generates around 15-20mV ripple at 600kHz (best case scenario with a pi-filter) which will pass through the LDOs without much attenuation as they have poor ripple rejection at this frequency.

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    \$\begingroup\$ That depends entirely on the ripple tolerated by whatever it's powering. \$\endgroup\$
    – user16324
    Commented Sep 15, 2016 at 19:14
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    \$\begingroup\$ Note that there exists LDOs with quite a significant suppression at 600 kHz. \$\endgroup\$
    – pipe
    Commented Sep 15, 2016 at 19:15

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There is no one answer about how much ripple is too much, because that depends on the devices being powered.

Yes, LDOs don't attenuate high frequency ripple much, but much of it can be filtered out before the LDO with a chip inductor in series followed by the LDO input cap to ground.

All that said, 20 mV ripple on a 3.3 V supply should not cause trouble for an ordinary microcontroller or digital logic.

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