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LM2611: Use of coupled inductors, general questions

Ryan Short
Prodigy 10 points
Part Number: LM2611
Other Parts Discussed in Thread: TIDA-01457

I need a -3.81 .1A typical, .15A max regulator.  It will power RF circuitry, so it needs to be quiet as possible.

I’m more of a digital designer, and definitely out of my comfort zone with switchers.  I’m using the LM2611 Cuk converter since I’ve read the Cuk topology inherently produces less noise.  I’m not concerned with cost of components, marginally concerned with board space.

 Here is my design so far.

 I did my best to use the equations to determine component values.  Some comments on the datasheet – it took a while to figure out D is duty cycle, and Ts is the period of 1.4MHz.

 Questions:  (the first three are the most important, but I hope you can answer the remaining questions also.)

  1.  How do my values look?  Any recommendations?
  2.  I read that using coupled inductors further reduce noise, but the datasheet doesn’t mention how to incorporate them.  Can I simply use a 10uH coupled inductor, and everything else works out as if I’m using two 22uf caps (I know 10uf isn’t exactly ½ of 22uf)
  3. Is there a way to simulate this so I can ensure current ripple is approx. 40%?  I tried downloading your simulation tool with no success, and it seems like I read this particular part isn’t supported by the simulation tool.
  4.  Under what conditions would it be an advantage to use different values for L1 and L2?
  5.  For input cap, as long as you are using a smaller cap next to the IC (low inductance), is the value of the larger cap generally the bigger the better?  
  6.  Going through Equation 9 to determine output capacitance, I came up with 44uf.  Is this another case of the more capacitance and less ESR the better? 
  7.  There will be some bulk capacitance after a few feet of power cable.  Do I have to take that into consideration?
  8.  In general are the inductor values determined by Vin vs Vout, and you just need to select an inductor that has sufficient saturation current?   
  9.  I don’t see any guidance for the value of Ccuk.  The examples use either 1uf or 2.2uf.  What affects the value of Ccuk?

 I appreciate any help or insight you can give.   Also, if it makes a difference, all of the smaller caps are 0603

 Thanks,

   Ryan