On Fri, 11 May 2007 10:53:17 +1200, Richard Prosser wrote:
> Hi All,
> I'm looking for suggestions for a reset chip to be used with an M16C62
> running off 3.3V.
>
> Main requirements are:- readily available, small & cheap. No bells or
> whistles required.
>
> Also a LDO 3V3 linear reg for about 40mA current drain. Input Voltage is
> about 4.5V. Again - small cheap & available.

This is kind of a loaded (or unloaded, depending how you look at it)
question.

This sounds a lot like a very low power battery operated system. That's
about all I've been designing the past 2 or 3 years so I've gone through
this exercise a lot. Performance, cost and size is really a "system"
specification as much or probably more than a "chip level" specification.

You don't really mention anything about performance, i.e. dropout voltage
required, Iq, noise, etc. Those requirements will lead you to a lot of
difference potential devices and eliminate many others.

Cost is a relative thing too -- for instance a lot of LDO regulators need a
tantalum or other low esr filter capacitor and often will specify a range
of filter cap esr over which they'll be stable. Others will allow ceramic
chip caps to be used, which can save a lot of cost right there and possibly
size too. Iq specifications can range all over the place for different
devices under all different kinds of conditions -- it may matter in your
application or it may not.

That said, I've found TI's supervisors and LDOs to be some of the best
available (I'll include Burr-Brown with them since TI owns them now).
Really excellent performance across a lot of different requirements with
reasonable chip cost, low system cost and excellent performance. Good
availability too.

Microhip's parts have tended to be low cost, available, but mediocre
performance. Some of their supervisor chips are quite good. I recently used
the MCP12x family but it has an odd pinout as compared to most of the other
SOT-23 supervisors out there. I'm not a big fan of their LDOs, they're OK
but middle of the road performance-wise. They do make some nice low voltage
CMOS op-amps with good performance.

Maxim is, well, Maxim. Good parts, high cost, made of unobtanium.

National doesn't have many high performance parts (really low Iq, Vdropout,
etc.) but they tend to be really cheap and usually available. If
performance isn't your top requirement but low cost is then they may have
some parts that suit.

On-Semi... somewhere in the spectrum between TI and National. Usually very
cost effective, performance is better than average. Sometimes availability
is a problem though. If you can get them at Digikey you are usually fine.

Linear Technology makes really good stuff, but kind of pricey. Usually
decent availability but sometimes also made of unobtanium.

Analog Devices... excellent parts, cost is much better than it used to be
and availability is getting better too. I always look at them before I'm
done searching for new low voltage analog parts.

Those are the major suppliers I'd look at. I'm sure I forgot some off the
top of my head. TI is almost always where I start first as they have an
excellent parametric search facility on their site, their parts are almost
always a good value and Digikey is a stocking distributor for them. TI has
an excellent sampling program and samples are shipped direct from Digikey
(usually overnight or 2nd day).

Probably not what you wanted to hear but the questions you asked always
remind me of someone asking "What kind of car should I buy?"... ;-)

OK... I'll take a flyer and answer your main questions: I'd look at the
Microchip MCP120/121 family of supervisors. Cheap and really low Iq. SOT-23
package.

For the LDO I'd look at the TI TPS715xx family. SC70-5 package, can use a
very small ceramic output cap. Very low Iq and low dropout voltage. If you
need an LDO with an enable function, the TPS793xx family is good too. TI
has a lot of great LDOs in small packages.

Matt Pobursky
Maximum Performance Systems



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