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'[PIC] Question about MAX232A'
2005\05\14@124544 by Kenasw

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I downloaded the datasheet for MAX232A (from farnell) and it seems
that I need 5x0.1uF capacitors to make this chip happy. I was just
wondering if I should choose electrolytic type capacitors or will anything do, since 0.1u is 100n, which is small even when it is not
electrolytic.

tia.

2005\05\14@132422 by Dave Turner

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I thought the MAX232A was the one that had all the internal capacitors
- are you sure you have the datasheet for the 232A, and not the 232
(which i believe does need capacitors)?

On 5/14/05, spam_OUTkenaswTakeThisOuTspambtinternet.com <.....kenaswKILLspamspam@spam@btinternet.com> wrote:
> I downloaded the datasheet for MAX232A (from farnell) and it seems
> that I need 5x0.1uF capacitors to make this chip happy. I was just
> wondering if I should choose electrolytic type capacitors or will
> anything do, since 0.1u is 100n, which is small even when it is not
> electrolytic.
>
> tia.
> -

2005\05\14@133329 by Bob Barr

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IIRC, MAX232x devices always need external capacitors. The "A" version
needs smaller caps than the older "non-A" version.

It's the MAX233 devices that have internal caps.


Regards, Bob


On Sat, 14 May 2005 18:24:17 +0100, Dave Turner wrote:

>I thought the MAX232A was the one that had all the internal capacitors
>- are you sure you have the datasheet for the 232A, and not the 232
>(which i believe does need capacitors)?
>

2005\05\14@133607 by Spehro Pefhany

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At 05:45 PM 5/14/2005 +0100, you wrote:
>I downloaded the datasheet for MAX232A (from farnell) and it seems
>that I need 5x0.1uF capacitors to make this chip happy. I was just
>wondering if I should choose electrolytic type capacitors or will
>anything do, since 0.1u is 100n, which is small even when it is not
>electrolytic.

Use ceramics with decent dielectric characteristics (eg. X7R) and
sufficient voltage rating. They are small, cheap and reliable.
In some cases you may wish to use higher than  the 0.1uF (see curves).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
>>>Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2005\05\14@140011 by Kenasw

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> Use ceramics with decent dielectric characteristics (eg. X7R) and
> sufficient voltage rating. They are small, cheap and reliable.
> In some cases you may wish to use higher than  the 0.1uF (see curves).

Are ceramics  also plarised like electrolitic, can't I use just any
old capacitor I can find?

2005\05\14@140420 by Kenasw

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> IIRC, MAX232x devices always need external capacitors. The "A" version
> needs smaller caps than the older "non-A" version.
>
> It's the MAX233 devices that have internal caps.

Is there any down side to the MAX233(A) due to the internal
capacitors, or will it be a good choice instead of MAX232(A) ?

>
>
> Regards, Bob
>

2005\05\14@143242 by Vic Fraenckel

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Go to http://www.max-ic.com (IIRC) and get the official data sheet for the MAX232.
You will find that any flavor of the '232 needs external electrolytic caps.
However, there are other ICs in this family that do not need any external
caps.

HTH

Vic
________________________________________________________

Victor Fraenckel - The Windman
victorf ATSIGN windreader DOTcom
KC2GUI


2005\05\14@143244 by Jan-Erik Soderholm

face picon face
kenasw@btinternet.com wrote :

> Is there any down side to the MAX233(A) due to the internal
> capacitors, or will it be a good choice instead of MAX232(A) ?

Hint, check the prices !

MAX232 from Maxim at Digikey : aprox $4 ea.
MAX233 from Maxim at Digikey : from $7 ea.

Also :
MAX232 from Texas at Digikey : $0.90 (!).

But of course, if price isn't an issue... :-)

Jan-Erik.



2005\05\14@153222 by olin_piclist

face picon face
kenasw@btinternet.com wrote:
> I downloaded the datasheet for MAX232A (from farnell) and it seems
> that I need 5x0.1uF capacitors to make this chip happy. I was just
> wondering if I should choose electrolytic type capacitors or will
> anything do, since 0.1u is 100n, which is small even when it is not
> electrolytic.

Ceramics have much better characteristics, and at that capacitance and
voltage they are readily and cheaply available.  I don't know of any
electrolytic that is only 100nF, at least not in the 10s of volts range.

Even better, I would use 1uF ceramics.  These are now readily available and
about as cheap as 100nF.  Some of the MAX232 type chips work with 100nF, and
some require at least 1uF.  I haven't seen any variant that doesn't work
with 1uF.  This will also give you a stronger and cleaner + and - voltage
drive.

For example, I used 1uF ceramics on the RSLink RS-232 converter
(http://www.embedinc.com/products).  This allows using whatever the best
deal of the week is in MAX232 chips.  The current batch uses a TI chip,
which requires 1uF minimum if I remember right.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\14@153813 by olin_piclist

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kenasw@btinternet.com wrote:
> Is there any down side to the MAX233(A) due to the internal
> capacitors,

Yeah, cost.  Unless you're PCB is really tight, it's not worth it.

*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\14@162737 by Spehro Pefhany

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At 06:59 PM 5/14/2005 +0100, you wrote:
> > Use ceramics with decent dielectric characteristics (eg. X7R) and
> > sufficient voltage rating. They are small, cheap and reliable.
> > In some cases you may wish to use higher than  the 0.1uF (see curves).
>
>Are ceramics  also plarised like electrolitic,

No, they are not polarized like an electrolytic capacitor.

>can't I use just any
>old capacitor I can find?

If it's your parts, I suppose you can do whatever you like with them.
Just about any part with sufficient voltage rating and around the right
capacitance or more will probably be functional at room temperature.

Capacitance, voltage rating, temperature effects, ESR, lifetime, cost,
PCB real estate, and so on might enter into a rational design
consideration, however.

0603 0.1uF 25V X7R ceramic caps are a penny or less each and take up
precious little precious PCB real estate. If it's just an occasional-use
set-up port, then that's what I'd use. You can even get them with leads
if your technology level is set to "nostalgia". As Olin says you can get
1uF ceramics for reasonable prices with reasonable dielectrics these days,
but you'd probably want to give some thought to the optimum case size and the
proper voltage rating for each part(the latter varies with the place in the
MAX232 circuit, the way you decide to connect the caps, and with how
conservative you are).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
>>>Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2005\05\14@215850 by Matt Pobursky

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On Sat, 14 May 2005 15:32:18 -0400, Olin Lathrop wrote:
> Even better, I would use 1uF ceramics.  These are now readily available and
> about as cheap as 100nF.  Some of the MAX232 type chips work with 100nF, and
> some require at least 1uF.  I haven't seen any variant that doesn't work
> with 1uF.  This will also give you a stronger and cleaner + and - voltage
> drive.

Olin's suggestion is a good one and I've been doing the same thing for
the past couple years on all my new designs.
Another good tip along the lines of "killing two birds with one stone" is to use a MAX3232 instead of a MAX232(A). They are pin compatible with the MAX232(A), about the same price as a MAX232A and (most
importantly) work with 3V to 5V supplies. I do more 3V designs these
days than 5V so it's really nice to only have to stock one part for
either voltage. They also work with ceramic caps (I use 470nF to 1uF)
and they're made by the usual suspects - Maxim, TI, Sipex, ST, et. al.

Matt Pobursky
Maximum Performance Systems

2005\05\14@231250 by Spehro Pefhany

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At 08:58 PM 5/14/2005 -0500, you wrote:
>Another good tip along the lines of "killing two birds with one stone"
>is to use a MAX3232 instead of a MAX232(A). They are pin compatible
>with the MAX232(A), about the same price as a MAX232A and (most
>importantly) work with 3V to 5V supplies. I do more 3V designs these
>days than 5V so it's really nice to only have to stock one part for
>either voltage. They also work with ceramic caps (I use 470nF to 1uF)
>and they're made by the usual suspects - Maxim, TI, Sipex, ST, et. al.
>
>Matt Pobursky
>Maximum Performance Systems

How have you found the reliability of those units? Had one failure (ST).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspam_OUTspamTakeThisOuTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




2005\05\15@021914 by Matt Pobursky

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On Sat, 14 May 2005 23:17:37 -0400, Spehro Pefhany wrote:
> At 08:58 PM 5/14/2005 -0500, you wrote:
> >Another good tip along the lines of "killing two birds with one stone"
> >is to use a MAX3232 instead of a MAX232(A). They are pin compatible
> >with the MAX232(A), about the same price as a MAX232A and (most
> >importantly) work with 3V to 5V supplies. I do more 3V designs these
> >days than 5V so it's really nice to only have to stock one part for
> >either voltage. They also work with ceramic caps (I use 470nF to 1uF)
> >and they're made by the usual suspects - Maxim, TI, Sipex, ST, et. al.
> >
> >Matt Pobursky
> >Maximum Performance Systems

> How have you found the reliability of those units? Had one failure (ST).

I've used a few Maxim parts, a moderate number of ST parts (100's) and
lots of TI parts (1000's). I haven't seen any failures with any of them
yet. I did notice the ST parts seemed to be somewhat noisy on their
charge pump outputs but it didn't seem to affect the operation at all.
I haven't used any in a medical design yet (although I will be later
this summer) and that will probably be revealing as they will get
zapped with up to 18KV for ESD testing.

Matt Pobursky
Maximum Performance Systems

2005\05\15@071006 by Kenasw

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face
It is better if this device could work from 3V as well, but the
strange thing is that in the data sheet it actually reads

maximum ratings:
supply voltage: -0.3v to +6V

This is very strange, as it would suggest that 0V is a permitted
supply, i.e. it will work with no supply voltage????

here is the datasheet

pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf

2005\05\15@083441 by Jan-Erik Soderholm

face picon face
kenasw@btinternet.com wrote :

> It is better if this device could work from 3V as well, but the
> strange thing is that in the data sheet it actually reads
>
> maximum ratings:
> supply voltage: -0.3v to +6V
>
> This is very strange, as it would suggest that 0V is a permitted
> supply, i.e. it will work with no supply voltage????

I can't see any ":-)", but you *must* be joking, right ? :-)

Can you point out where they say that that the device will
actualy "work" at 0V ? No, you can't.

On the other hand, they say in a footnote to the "Absolute
Maximum Ratings" table, that :

"These are stress ratings only, and functional operation of
the device at these or any other conditions beyond those
indicated in the operational sections of the specifications
is not implied."

Pefectly clear, IMHO.

Read "Operating Supply Voltage" on page 3.
(Well, maybe better to read it all... :-) )

Best Regards,
Jan-Erik.

> here is the datasheet
>
> pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf
> --



2005\05\15@085619 by olin_piclist

face picon face
kenasw@btinternet.com wrote:
> maximum ratings:
> supply voltage: -0.3v to +6V
>
> This is very strange, as it would suggest that 0V is a permitted
> supply, i.e. it will work with no supply voltage????

No, it only states the supply voltage range that will not damage the chip.

*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\16@033058 by Electron

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Maximum ratings doesn't mean "operative ratings".

Place less than -0.3V or more than +6.0V and you will destroy it.
It means just this, it doesn't mean that it actually operates at
-0.3V..


At 12.09 2005.05.15 +0100, you wrote:
{Quote hidden}

>-

2005\05\16@050028 by Alan B. Pearce

face picon face
>I haven't used any in a medical design yet (although I will be later
>this summer) and that will probably be revealing as they will get
>zapped with up to 18KV for ESD testing.

This is where the E version of the maxim parts may help you - rated for
quite high ESD pulses. They are applying the E rating to a fair number of
the interface chips these days.

2005\05\16@083624 by Matt Pobursky

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Thanks Alan for reminding me. I was aware of them (as well as 'E' type
RS485 drivers) but you jogged my memory and maybe others on the list.

Matt Pobursky
Maximum Performance Systems

On Mon, 16 May 2005 10:00:05 +0100, Alan B. Pearce wrote:
> >I haven't used any in a medical design yet (although I will be later
> >this summer) and that will probably be revealing as they will get
> >zapped with up to 18KV for ESD testing.

> This is where the E version of the maxim parts may help you - rated for
> quite high ESD pulses. They are applying the E rating to a fair number of
> the interface chips these days.

2005\05\16@084649 by alan smith

picon face
FWIW...I stay as far away from Maxim for any sort of
design that needs to be built in quantity.  You can
design a part in, find stock today but when you go (or
your CM) to order for a large build...if they don't
have stock, forget it.  They might get around to
building some parts later in the year.  For a company
that has so many cool parts, really a shame that they
get the reputation for this.  And I am talking about
10K annual so its not like just a few hundred.  Unless
you are using millions they just don't seem all that
interested.  Least thats my experiance with them.


--- kenaswspamspam_OUTbtinternet.com wrote:
{Quote hidden}

> --

2005\05\16@092855 by Spehro Pefhany

picon face
At 05:46 AM 5/16/2005 -0700, you wrote:
>FWIW...I stay as far away from Maxim for any sort of
>design that needs to be built in quantity.  You can
>design a part in, find stock today but when you go (or
>your CM) to order for a large build...if they don't
>have stock, forget it.  They might get around to
>building some parts later in the year.  For a company
>that has so many cool parts, really a shame that they
>get the reputation for this.  And I am talking about
>10K annual so its not like just a few hundred.  Unless
>you are using millions they just don't seem all that
>interested.  Least thats my experiance with them.

In this case, there are second sources, although the MAX232
is perhaps better in that regard. Maxim's prices are a LOT higher
IME.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
@spam@speffKILLspamspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




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