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'[EE] LVTTL Schmitt trigger non-inverting buffer - '
2006\03\08@123241 by Michael Rigby-Jones

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Help!

Requirements:

Supply voltage 3.3v
Input thresholds LVTTL (0.8v/2.0v)
Output thresholds CMOS (driving an AVR)
Schmitt Trigger
Smallest package possible e.g. Philips Pico-logic or TI's NanoStar/NanoFree die-with-solder-bumps style would be perfect.

I've been scouring various manufacturers web sites and nothing I can see comes close, in particular I can't find a Schmitt trigger device with true LVTTL compliant inputs.  Do they exist?

Thanks

Mike



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2006\03\08@135609 by Spehro Pefhany

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At 05:32 PM 3/8/2006 +0000, you wrote:
>Help!
>
>Requirements:
>
>Supply voltage 3.3v
>Input thresholds LVTTL (0.8v/2.0v)
>Output thresholds CMOS (driving an AVR)
>Schmitt Trigger
>Smallest package possible e.g. Philips Pico-logic or TI's
>NanoStar/NanoFree die-with-solder-bumps style would be perfect.
>
>I've been scouring various manufacturers web sites and nothing I can see
>comes close, in particular I can't find a Schmitt trigger device with true
>LVTTL compliant inputs.  Do they exist?
>
>Thanks
>
>Mike

You could always series two inverting ST in one tiny package such as the
SC70-6 NL27WZ14.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2006\03\08@150148 by Dwayne Reid

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At 10:32 AM 3/8/2006, Michael Rigby-Jones wrote:
>Help!
>
>Requirements:
>
>Supply voltage 3.3v
>Input thresholds LVTTL (0.8v/2.0v)
>Output thresholds CMOS (driving an AVR)
>Schmitt Trigger
>Smallest package possible e.g. Philips Pico-logic or TI's
>NanoStar/NanoFree die-with-solder-bumps style would be perfect.
>
>I've been scouring various manufacturers web sites and nothing I can
>see comes close, in particular I can't find a Schmitt trigger device
>with true LVTTL compliant inputs.  Do they exist?

SN74AUP1T97DBVR
SN74AUP1T98DBVR

May not be close enough but SN74AUP1G58DBVR

These are all SOT-23 but I'm pretty sure they are available in
smaller packages.

dwayne

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2006\03\09@003202 by Vasile Surducan

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On 3/8/06, Michael Rigby-Jones <Michael.Rigby-JonesspamKILLspambookham.com> wrote:
> Help!
>
> Requirements:
>
> Supply voltage 3.3v
> Input thresholds LVTTL (0.8v/2.0v)
> Output thresholds CMOS (driving an AVR)
> Schmitt Trigger
> Smallest package possible e.g. Philips Pico-logic or TI's NanoStar/NanoFree die-with-solder-bumps style would be perfect.
>
> I've been scouring various manufacturers web sites and nothing I can see comes close, in particular I can't find a Schmitt trigger device with true LVTTL compliant inputs.  Do they exist?

http://focus.ti.com/docs/prod/folders/print/sn74auc1g17.html

greetings
Vasile

2006\03\09@063256 by Michael Rigby-Jones

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{Quote hidden}

Thanks Vasile, but that's 2.7v maximum supply.  I need to go up to 3.3v +5%

Regards

Mike

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2006\03\09@063302 by Michael Rigby-Jones

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{Quote hidden}

Unfortunately these have LVCMOS thresholds rather than LVTTL.

>
>May not be close enough but SN74AUP1G58DBVR

It would probably work, but the customer is very specific about having LVTTL logic thresholds.  The above part has quite a wide range on the thresholds, which varies proportionaly with supply voltage (typical schmitt trigger behaviour), which is the main stumbling block I am having with any parts I have found.

Thanks for the suggestions though.

Regards

Mike

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2006\03\09@065654 by Michael Rigby-Jones

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{Quote hidden}

I would be happy to do that, but as with some Philips products I have found, they appear to have a VERY loose idea of what LVTTL is.  That part says LVTTL compliant at 3volts (which would be awkward anyway) but the min/max thresholds at that voltage are 2.2v and 0.6 rather than 2.0v and 0.8v.  Probably close enough from my point of view, but customer is insistant on meeting the actual LVTTL levels after problems with another vendors part.

Regards

Mike

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2006\03\09@072415 by Alan B. Pearce

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>Probably close enough from my point of view, but
>customer is insistant on meeting the actual LVTTL
>levels after problems with another vendors part.

Hmm, what were the specified levels for the part the customer wants to
replace ??

2006\03\09@072658 by Spehro Pefhany

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At 11:56 AM 3/9/2006 +0000, you wrote:

>I would be happy to do that, but as with some Philips products I have
>found, they appear to have a VERY loose idea of what LVTTL is.  That part
>says LVTTL compliant at 3volts (which would be awkward anyway) but the
>min/max thresholds at that voltage are 2.2v and 0.6 rather than 2.0v and
>0.8v.  Probably close enough from my point of view, but customer is
>insistant on meeting the actual LVTTL levels after problems with another
>vendors part.

It's within the LVTTL spec, but with reduced noise margin (200mV rather
than 400mV)

The output spec is 400mV/2.4V.

But you'd have to operate it at 3.0V rather than 3.3V, as you note.

Maybe you're going to have to design your own ST with a comparator and
some 1% resistors if you really need to meet this spec. But then your
size constraint bites you on the butt..

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
TakeThisOuTspeffEraseMEspamspam_OUTinterlog.com             Info for manufacturers: http://www.trexon.com
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2006\03\09@072935 by Russell McMahon

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flavicon
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> ... but the customer is very specific about having LVTTL logic
> thresholds.

I wondered, "Why?"

Which was answered by -

> but customer is insistant on meeting the actual LVTTL levels after
> problems with another vendors part.

I don't know how savvy the customer is, but it sounds like they are
falling into the all too common trap of telling you how they want
something done, rather than specifying what they actually require. In
this case I suspect that specs of 0.6V or 0.8V are by themselves
likely to be reasonably meaningless. One would need to ensure these
were worst case, were over temperature and supply voltage and phase of
the moon, and more. One man's / supplier's looser apparent spec may be
a better one if it is actually adhered to and a notionally better one
isn't.

Anyone system which has problems with levels of eg 0.6V versus 0.8V is
probably sailing too close to the wind for comfort in any case. When
reality strikes the system is in risk of doing so too.

I'd suggest that you ask the customer to let you *engineer* / *design*
the system so that it is guaranteed to work, using whatever parts you
deem will do the job. What a novel idea :-). The alternative is to
risk giving them what they ask for but failing to deliver what they
want. Design may be difficult if the existing system is poorly enough
specd to not work with all brands of reasonably compatible ICs, but
finding out what it's limitations are and designing for them is
superior to follow a recipe book.



       RM


2006\03\09@073215 by Vasile Surducan

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On 3/9/06, Michael Rigby-Jones <RemoveMEMichael.Rigby-JonesspamTakeThisOuTbookham.com> wrote:
{Quote hidden}

You can't, you need a 2V input requirement and a 3.3V output requirement.
Use a 2V to 2.7V supply device with an open drain up to 3.3V.
I had this problem too and never found such a gate (except the buffer
level converter with many gates).

Vasile

2006\03\09@075417 by Michael Rigby-Jones

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{Quote hidden}

No, I need guarantee LVTTL input thresholds which are 0.8v and 2.0v for the maximum Logic 0 threshold and the minimum Logic 1 threshold.  The actual input voltage swing could be a maximum of 0-3.3 volts.

Regards

Mike

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2006\03\09@080243 by Michael Rigby-Jones

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{Quote hidden}

The story is that the product is built to meet a multi-source agreemant specification, and the logic thresholds are defined within that spec.  Clearly other vendors have had the same problem as us in meeting these levels...

I totaly agree with what you are saying though, I've seen this exact scenario too many times where a customer will concentrate on a trivial specification to the exclusion of all else due to some experience they have had in the past.  Unfortunately when these trivialities are holding back a potnential order, we have little choice.

Regards

Mike

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2006\03\09@092547 by Vasile Surducan

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On 3/9/06, Michael Rigby-Jones <@spam@Michael.Rigby-Jones@spam@spamspam_OUTbookham.com> wrote:
{Quote hidden}

http://focus.ti.com/docs/prod/folders/print/sn74aup1g17.html

For a trigger schmitd, there are different thresold levels than to a
normal LVTTL gate. And notice the LVTTL could be also supplied at
3.0V. So your customer must know exactly what he/she want.

greetings,
Vasile

2006\03\09@102138 by Michael Rigby-Jones

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{Quote hidden}

The spec we have been given is 0.8v/2.0v, so 0.6v/2.2v could concievably not work at all.

>The output spec is 400mV/2.4V.
>
>But you'd have to operate it at 3.0V rather than 3.3V, as you note.
>
>Maybe you're going to have to design your own ST with a
>comparator and some 1% resistors if you really need to meet
>this spec. But then your size constraint bites you on the butt..

Unfortunately this looks like it might be the only realistic solution.  Thanks for everyones input.

Regards

Mike

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