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ADP1706 Ripple problem

Question asked by Cymbele on Oct 14, 2013
Latest reply on Dec 21, 2013 by KurtBecker

I am a newbie power supply designer.

I have 44 mV of ripple (from my switching regulator)  going into my linear regulator at f=1MHz. I have Cin=Cout=4.7uF. The linear regulator is not reducing the ripple. I tried adding small value caps at the output of the regulator.The input/output caps are very close to the regulator. The PSRR is about -40 dB at 1MHz at the desired current.

Any suggestions? I have used linear regulators in the past without a hitch; this is the first app that the noise has not been filtered.

 

This is also happening on a related part the ADP1755.

 

Linear regulators

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