Hi,

On 15 Mar 99 at 13:38, Frank Cembrola wrote:
<snip>
> I am designing a circuit to generate the 13V programming voltage for the
> PIC. I confess I am less than an expert on switched mode design.
>
> After I looked at some literature, I came to the conclusion that maybe a
> MAX762 would be appropriate for my design.
<snip>

I would start with a higher DC and use linear regulators to generate
the 13V and 5V since they both are pretty low current for this kind
of application.  If you're using a wall cube to power your device
just go up to a higher voltage or one that gives AC instead of DC.
This way you will get nice, precise and clean voltage easily.

I've had bad experience with Maxim switchers (specifically the 639).
Switching noise, output FET easily destroyed (ESD?), high sensitivity
to layout and component selection.  I've also seen startup problems.

You'd have to work *very* hard to get good linear regulators to
misbehave.  Something like the LM2936 (5V) has internal current
limit, internal thermal shutdown, reverse battery protection, -50V
reverse transient protection, upto 40V input (quoting the datasheet
here).-40 deg C to +125 deg C and more...  Try to put one of those
Maxim's through these... (+ they're ~$1.00 in tube quantity compared
to over $2.5 for the maxim switcher)

And something else, the *last* (and it really was the last) time I
requested a quote on a Maxim component they quoted with 40 weeks
delivery time.  Even Digikey does not actually stock every Maxim
that's in their catalog - check their online system for availability
or you could be in for a *long* wait.

If you must have a switcher you should consider devices from Linear
Technology.

Hope this helps,
Guy - mlsirton@inter.net.il