Hello,

I am trying to design a DC/DC (8V down to 3.5 to 6VDC, 500ma) using
National LM2671 (http://cache.national.com/ds/LM/LM2671.pdf).

The section that discuss the input and output capacitor consideration
specify the capacitors by their max RMS current. However, some
capacitors data sheets do not specify this value and instead specify max
ESR.

My questions to the list are:

1. Is there a relation between capacitor max RMS current and max ESR and
if so, what is the formula  (does it assume max power dissipation by the
capacitor?).

2. Is it really critical to have low ESR or high current capacitors for
the input and/or output of the DC/DC ? What happens if I will use
'simple' capacitors, is it just a matter of efficiency ?

3. What kind of capacitors (electrolytes, tantalum, etc) are preferred
for this application (volume manufacturing), assuming that component
cost is very important ?

Thanks,

Tal



> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Richard Graziano
> Sent: Saturday, June 21, 2003 7:24 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: DSP (was: Square wave to sine wave - how?)
>
>
> I have not been following this thread, so I may be off base.
> But if you need one particular frequency, and do not require
> variable control, it would be easy to design a sinusoidal
> oscillator with a low impedance output buffer/driver.  This
> would have better quality (i.e., less distortion) than a
> converted square wave.  It may be easier also, to simply
> design a high purity oscillator.
>
> I apologize if this has already been discussed.
>
> Rich
> ----- Original Message -----
> From: "Randy Ott" <randy@THEOTTS.NET>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Saturday, June 21, 2003 1:27 AM
> Subject: Re: [PIC]: DSP (was: Square wave to sine wave - how?)
>
>
> > The DSP solution will allow you to generate very clean sine
> waves all
> > by itself.  Sounds like to me that what you really want is a DDS.
> > Then you
> can
> > generate sine waves from milli-Hertz to 10's of Mega-Hertz or more
> > with milli-Hertz resolution.
> >
> > ( I spelled out milli and Mega to avoid flames about wrong units )
> >
> > Randy Ott
> >
> > ----- Original Message -----
> > From: "John Nall" <jnall01@ALLTEL.NET>
> > To: <PICLIST@MITVMA.MIT.EDU>
> > Sent: Friday, June 20, 2003 5:07 PM
> > Subject: Re: [PIC]: DSP (was: Square wave to sine wave - how?)
> >
> >
> > > At 10:24 AM 6/20/2003 -0600, Tim Webb wrote:
> > >
> > > >Check out these URLs they might help provide a lot of
> information
> > > >that would allow you to  understand how to convert a square wave
> > > >into a sine wave.  Typically a filter can be designed to
> remove all
> > > >of the
> harmonics
> > > >after the fundamental frequency and that ideally would produce a
> perfect
> > > >sine wave.
> > > >
> > > >A Sine wave has only the fundamental frequency with no other
> > > >harmonics
> > >
> > > Roger that.  I had no idea that it was such a complicated thing to
> > > do!!   And this response is meant to express thanks to
> the others that
> > > responded (including Grumpy Olin :-)
> > >
> > > So it looks to me from going through the responses, that
> filtering
> > > is
> the
> > > way to go.  OK.  I can deal with that.  One further
> question to throw
> > > out:   As a Ham of about 36+ years (which probably
> entitles me to some
> > sort
> > > of pin) I feel pretty sure I can construct a filtering
> circuit.  But
> > > it ALSO looks like some digital signal processing (DSP)
> might come
> > > in handy here.  Anyone have any thoughts on that???
> > >
> > > John
> > >
> > > --
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