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'[EE:] 3V3 Reset Chip'
2007\05\10@185737 by Richard Prosser

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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.

Richard Prosser

2007\05\10@191304 by Gerhard Fiedler

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Richard Prosser wrote:

> I'm looking for suggestions for a reset chip to be used with an M16C62
> running off 3.3V.

I've used Microchip TC54.

> Also a LDO 3V3 linear reg for about 40mA current drain. Input Voltage
> is about 4.5V. Again - small cheap & available.

I've used REG101, but it may be too expensive for your application.

Gerhard

2007\05\10@193045 by Rolf

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As for the LDO, how about MCP1700 or MCP1702?

Rolf

Richard Prosser wrote:
{Quote hidden}

2007\05\10@193211 by Timothy J. Weber

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Richard Prosser wrote:
> Also a LDO 3V3 linear reg for about 40mA current drain. Input Voltage
> is about 4.5V. Again - small cheap & available.

I'm using Microchip MCP1702 lately.  Typical quiescent current of 2 uA,
around $0.40.
--
Timothy J. Weber
http://timothyweber.org

2007\05\10@225804 by Matt Pobursky
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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



2007\05\10@230410 by Matt Pobursky

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On Thu, 10 May 2007 19:32:00 -0400, Timothy J. Weber wrote:
> Richard Prosser wrote:
>> Also a LDO 3V3 linear reg for about 40mA current drain. Input Voltage
>> is about 4.5V. Again - small cheap & available.
>>
>
> I'm using Microchip MCP1702 lately.  Typical quiescent current of 2 uA,
> around $0.40.

Other than a moderately high dropout voltage (at low voltages) that looks
like a really nice part. I've added it to my list of parts to consider for
new designs!

Microchip really needs to improve their low voltage FET process (in
general).

Matt Pobursky
Maximum Performance Systems

2007\05\11@035257 by Russell McMahon

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> 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.

They make the LM2936 just to provide the exception to the rule :-).
Excellent Iq, excellent dropout, costs far far too much.

> Those are the major suppliers I'd look at.

There are some really nice and ultra low cost parts available in
Taiwan that seldom see the light of day elsewhere. Whether it's worth
pursuing such depends on volumes.



       Russell

2007\05\11@045429 by Richard Prosser

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Matt , Russell & others.

Thanks for taking the time & trouble to answer so completely.
I also did a hunt on the web for suitable items but it's easy to miss
a particularly useful part wen you're looking at specs on one page &
prices (web prices) on another. So I thought a quick query to the list
may help me find something I'd otherwise miss.

In the initial design we'll probably go without an external reset chip
but may provide for one "just in case".

FWIW I have decided to get quotes for the National LP2980APM5-33 with
the Texas TPS76033 as a second source for the regs. We are currently
using a 800mA device at about $US0.40 each so if I can't get a
significant reduction on this the I won't bother to change as the
hassle of supporting 2 part types is significant. However at ~10k/year
there is an incentive to findsomething cheaper.

Also the Fairchild FAN2519 looks promising as it may be able to double
as the reset chip as well - but the pinout is different. There is a
Texas chip that may perform both functions also and  again the pinout
may vary - I have still to check -


There is also a MAXIM chip that provides a delayed reset - but no
second source  and probably hard to ensure a reliable supply! Also it
costs about $US1.00.

Quiescent current is not of concern, the product will run in telephone
exchanges with maybe several kA-hr of backup battery! - and when it's
off it's becaude there is no supply!
Noise & accuracy is not of too much concern either - no analogues to
worry about or picky PLL requirements to meet.

The source supply is a fairy stable 4.5V line from a switcher so the
LDO requirement is actually a bit of an exaggeration. Unfortunately I
don't think the 4.5V is stable enough to wind down to 3.3V and run
without a regulator. Might try it later on though. But I need more
than 4V  for the backlight but the display is 3.3V max.so would  have
to provide a separate backlight supply.........

Fair comment re the tantalums however - that is something to consider..

Thanks again

Richard

On 11/05/07, Matt Pobursky <spam_OUTpiclistTakeThisOuTspammps-design.com> wrote:
{Quote hidden}

> -

2007\05\11@062628 by Alan B. Pearce

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>Microchip really needs to improve their low voltage FET process
>(in general).

Zetex seem to have themselves well sorted for LV FETS.

For "Ultra Low dropout" LDO they have a 3.3V with 20mV dropout voltage,
300mA current capability (ZLDO330). They also have 4.85V and 5V versions of
it. Price quoted as $0.811/1k on their web page, which is around twice what
someone else was quoting for an LDO, but I haven't compared the specs. These
ones seem to have a high input voltage rating.

They also have "Micropower Low Dropout" regulators. ZXCL330 quotes 85mV and
150mA with 25uA Iq. $0.301/1k. SC70-5 and SOT23-5 packages.

haven't used any of them though, so cannot comment on how well they work.

http://www.zetex.com/


2007\05\11@111721 by Timothy Weber

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Matt Pobursky wrote:
> On Thu, 10 May 2007 19:32:00 -0400, Timothy J. Weber wrote:
>> Richard Prosser wrote:
>>> Also a LDO 3V3 linear reg for about 40mA current drain. Input Voltage
>>> is about 4.5V. Again - small cheap & available.
>>>
>> I'm using Microchip MCP1702 lately.  Typical quiescent current of 2 uA,
>> around $0.40.
>
> Other than a moderately high dropout voltage (at low voltages) that looks
> like a really nice part. I've added it to my list of parts to consider for
> new designs!

And it asks for just 1uF ceramic in and out - no tantalum required.  I'd
be interested to hear what you think if you get a chance to try it.

Thanks for your other recommendations too.
--
Timothy J. Weber
http://timothyweber.org

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