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Re: ADM660 input switching noise

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Hi Alex,

Looks like you've made a lot of progress so far.  Here's a couple of comments in response to your results and questions:

1.  Ceramic caps:  I'm surprised that ceramic capacitors don't help your ripple--especially for the output cap.  Ceramics have much lower ESR's then tantalum.  Try using the same value (10uF) the tantalum ones and see if that doesn't help. 

2.  Vout ripple:  The short spike in the Vout ripple is due to parasistic inductances. Probably in the output capacitor or in the trace to the output capacitor.  Ceramics usually have a lower ESL than tantalums, so that may help with the parastic inductance spike.  Or you can always add a small LC filter to the output. 

3.  Stable Output:  The output of an inverting charge pump is alway "stable."  Meaning it does not oscilallate because it has no feedback path (it is not sensing the voltage and adjusting any of the power delivery).  So it is never unstable.  However, like all switching converters, it will have output voltage ripple, which is normal. 

  - Jon


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