You may want to rethink your choice of parts.  The SC4517A is going out/ is
out of production.  See Mfr'r site:

http://www.semtech.com/products/power_management/non_synchronous_single_outp
ut/sc4517a/

Rich

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
kenn
Sent: Tuesday, November 17, 2009 4:54 PM
To: piclist@mit.edu
Subject: Re: [EE] Buck specs & inductors



PICdude-3 wrote:
> 
> Doing the math for an SC4517A buck regulator using their datasheet,  
> and right off the bat it asks me for something I'm not sure of --  
> peak-to-peak inductor current.  I'd think that I should just specify  
> the in/out voltages, output current and the output ripple voltage, and  
> it would then determine the peak-to-peak inductor current, which would  
> then tell me what inductor I would need.
> 

The data sheet says that the switch in your chosen part is rated for 1.5A...
so I would take that as the peak inductor current... cos any higher risks
burning out your IC.

PICdude-3 wrote:
> 
> Some other Q's ...
> 
> - Some inductor datasheets only state Max Current.  Would this be Irms  
> or Isat?
> - Is it okay to drop in an LDO after a buck converter to really smooth  
> things out?  Yes, I'd have to raise the buck output voltage.
> 

Just guessing, but I'd assume that an inductor's "Max Current" would be the
highest design current before saturation. Otherwise, maybe it's the max
current before the inductor bursts into flame... :O

By LDO, do you mean a linear regulator? You can do that but it's kind of
overkill. I expect that the buck regulator should be "stiff" within its
designed output range, and any ripple at the switching frequency (~ 1 MHz)
is easy to filter out.

HTH...

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