3.3v <> 5v interfacing @ 15Mhz

On 2006-11-26, Alison <alison@logicsaysNOSPAM.com> wrote:
> rickman <gnuarm@gmail.com> wrote in message
> news:1164503030.194876.309670@45g2000cws.googlegroups.com...
>>
>> The drawing from my other post did not inititially include the BCE
>> markings, so I added them.  You can check the data sheet for the part
>> to see where each function is on the package.  This will be very
>> non-critical in terms of transistor selected or resistor value.  Just
>> make sure you use an NPN or N-channel device.
>>
>
> tnx :-)
>
> The reason why I believed that a 3.3v '1' would register as a '1' on a CMOS
> dsPIC port is that there are quite a few examples on the net that say it
> works...  That was my mistake, believing what I read on the Internet.

isn't High typically specced as anything above 2/3 VCC.... (that'd be 3.33v)

What voltage are they running the DSPIC ?

> "It will work, but isn't within spec' so it's unreliable.  It's reliable at
> a few Mhz at very most, when the parts are designed to go upto about 30Mhz."
>
> "dsPIC parts CANNOT be directly interfaced to 3.3v devices!"

if you power the PIC from 3.3V it'll probably work just fine

-- 

Bye.
   Jasen

Alison wrote:
> It's looking alot tidier now.  Should keep me going with the firmware
> development until the PCBs appear.
> 
> http://www.logicsays.com/pub/WeST/WeST_v2.jpg
> 
> The board with the chip on it has most of what's required SPI side condensed
> down.  There's a board under that takes care of getting the Vdd/Vss to the
> all of the pins (PICs are picky about that).  And the ribbon cable goes off
> to a kind of hybrid SCSI bus implemented on a 68000 processor DMA bus.
> 
> Thanks again for your help :-)  Thanks to all of you :-)

  To give yourself some more margin, look at adding some parallel C to
the series resistor (same peaking/matching princple as a scope probe), 
on those lines that need to do 5V to 3V.

  What you are making is a capacitive divider (high frequency) that 
matches the resistive divider (low frequency), and it allows the
resistor values to increase without a speed penalty (for lower power).
  eg  If the total load shunt C is 20pF, you'll need appx 40pF.

  Avoid transistors, they will be too slow.

  -jg

Jim Thompson wrote:

> On Sun, 26 Nov 2006 13:42:53 -0700, Jim Thompson
> <To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote:
> 
> [snip]
> 
>>Allowing a static (and *undefined* BTW... 1mA if you're lucky) current
>>flow is NOT good engineering practice, and it's NEVER done in
>>well-designed ASIC's.
>>
>>To see how a 3.3V Logic Level to 5V Logic Level Translator is done
>>properly (in ASIC's designed specifically for that purpose), see...
>>
>>http://analog-innovations.com/SED/LogicLevelTranslator.pdf
>>
> 
> [snip]
> 
> Also: Static current for this structure is zero, except for nA's of
> leakage.

.. When driven to the rails ?

Interesting circuit; do you have the plots of Icc vs Vin,
increasing and decreasing ?
And also Icc into/out of 5V and 3.3V rails ?

Limits of Vcc delta's ?

-jg

Alison wrote:
> Mike Monett <No@email.adr> wrote in message
> news:Xns988770837D9B4Noemailadr@208.49.80.251...
> >   "Alison" <alison@logicsaysNOSPAM.com> wrote:
> >
> >   > Have a look at this picture to save 1000 words;
> >
> >   I hate to tell you this, but that solderless breadboard is about the
> >   worst thing you could be using. With edge rates of 10ns  and periods
> >
> >   I hope this helps. If you need any more information, please ask.
> >
> >   Regards,
> >
> >   Mike Monett
> >
> >   Antiviral, Antibacterial Silver Solution:
> >    http://silversol.freewebpage.org/index.htm
> >   SPICE Analysis of Crystal Oscillators:
> >    http://silversol.freewebpage.org/spice/xtal/clapp.htm
> >   Noise-Rejecting Wideband Sampler:
> >    http://www3.sympatico.ca/add.automation/sampler/intro.htm
>
>
> Hi Mike,
>
> Thanks for the info.  Reading through now.
>
> I'm going to try and get the circuit onto PCB in the next week or so.  The
> final design will also switchover to TQFP devices.  At the moment it just
> about serves the purpose of providing a base from which I can develop the
> firmware for the chip.
>
> To be honest, I hate breadboard!!  But am not in a position to create PCBs.
> The closest I can do is 0.1" pitch, printing out the circuit, drilling the
> holes through, dalo-ing out the bits I want to keep, and then ferric-ing off
> the rest.  That's just toooooo messy.
>
> Prototype PCBs here in the UK are still astromonically expensive compared to
> the US.

There are a few other things you might want to consider.  I don't know
how many of these you plan to make or how they will be used.  But
anytime you have external signals, it is a good idea to protect them
from ESD.  If you can work with a real PCB design (made by a PCB
maker), you can use a part that might be better.  Here is one I found
at TI.

http://focus.ti.com/docs/prod/folders/print/txb0104.html

It provides 15 kV ESD protection and will do the level translation
without the resistors and messy circuitry.  It does not come in a 0.1"
DIP, but it is available in SOIC which is 0.05" pin spacing, large by
today's standards.  You should be able to get a few as free samples.
All things considered, something like this is the route I would take.
I don't know how SD card I/Os are typically protected, but this is
something you might want to take seriously.

If you want to have a PCB made for you inexpensively you can go to
Olimex which I think is in Eastern Europe.  http://olimex.com/  Olimex
will directly accept Eagle .BRD files without conversion to Gerber
format, but I find Eagle a bit of a PITA to learn.  FreePCB is a lot
more user friendly.  You can find it at http://www.freepcb.com/ with
support available in the online forum or at
http://tech.groups.yahoo.com/group/FreePCB/  I hope it catches on more
widely.

Oh, be sure to use lots of power and ground plane area, flood fill if
you go two sided.  This provides a good high frequency capacitor that
minimizes noise on the power planes.

Let us know how your design works out!

Mike Monett wrote:
>   Hi Alison,
>
>   Thanks for the reply.
>
>   You might  find breadboarding a lot more pleasant once  you  get the
>   hang of  working  with copperclad. It certainly  makes  working with
>   high frequency a lot easier, and a well-made board can even  be used
>   in place  of  a  pcb.  I like to  use  ordinary  hot  glue  to mount
>   components to  the  copper.  This works great  for  parts  that stay
>   cool:)
>
>   I'm still using prototypes I made years ago, and they work fine.

Maybe I don't undestand what you mean by "copperclad".  To me that is
the same as PCB.  Are you talking about mouting components to a
pre-etched general prototype board or a PCB that has *not* been etched
at all, or something else?

On Mon, 27 Nov 2006 21:53:13 +1300, Jim Granville
<no.spam@designtools.maps.co.nz> wrote:

>Jim Thompson wrote:
>
>> On Sun, 26 Nov 2006 13:42:53 -0700, Jim Thompson
>> <To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote:
>> 
>> [snip]
>> 
>>>Allowing a static (and *undefined* BTW... 1mA if you're lucky) current
>>>flow is NOT good engineering practice, and it's NEVER done in
>>>well-designed ASIC's.
>>>
>>>To see how a 3.3V Logic Level to 5V Logic Level Translator is done
>>>properly (in ASIC's designed specifically for that purpose), see...
>>>
>>>http://analog-innovations.com/SED/LogicLevelTranslator.pdf
>>>
>> 
>> [snip]
>> 
>> Also: Static current for this structure is zero, except for nA's of
>> leakage.
>
>.. When driven to the rails ?

Not quite to rails.

>
>Interesting circuit; do you have the plots of Icc vs Vin,
>increasing and decreasing ?

See (updated)....

http://analog-innovations.com/SED/LogicTranslatorConcept.pdf

>And also Icc into/out of 5V and 3.3V rails ?

V1 = 5V, V2 = 3.3V

>
>Limits of Vcc delta's ?
>
>-jg

I don't know an answer for that.  This presentation was just a
lash-up.  My actual ASIC implementation uses single-stage inverters
instead of the 74HC04's, so my sizing ability allows very low
overlaps... it's basically a form of hysteresis.

I'd guess that wildly disparate power supplies would present some slew
issues and give more overlap current... but I'd hazard a guess that
1.2V -> 5V would be easy.

                                        ...Jim Thompson
-- 
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Jim Thompson wrote:
> On Sun, 26 Nov 2006 18:29:28 GMT, Vladimir Vassilevsky
> <antispam_bogus@hotmail.com> wrote:
>
> >
> >
> >Jim Thompson wrote:
> >
> >>>>>Incredible. Designing complicated circuit instead of simply using
> >>>>>74HCT14 / 74HCT04 / zillion other HCT74xx and AHCTxx ICs.
> >
> >>>>You've just proved yourself an incredible dumb-shit ;-)
> > > Keep it up.  Everybody is realizing the "value" of your consultancy
> > > ;-)
> > >
> > > You read a data sheet without understanding.
> > >
> > >                                         ...Jim Thompson
> >
> >
> >
> >If you have something meaningful to say, then go ahead and tell us.
> >Otherwise have the courage to admit that you just made a fool of
> >yourself, my dear analog desiner.
> >
> >
> >Vladimir Vassilevsky
> >
> >DSP and Mixed Signal Design Consultant
> >
> >http://www.abvolt.com
>
> Apply +2.4V Input to an HCTxx running on VDD = +5V and what happens?
>
>                                         ...Jim Thompson

Maybe I'm dense but isn't that that pretty much the intended
application for HCT parts?
specified in the datasheet down to much extra current consumption when
going to limits
of Vi and Vcc

-Lasse

On 27 Nov 2006 09:00:49 -0800, langwadt@ieee.org wrote:

>
>Jim Thompson wrote:
[snip]
>>
>> Apply +2.4V Input to an HCTxx running on VDD = +5V and what happens?
>>
>>                                         ...Jim Thompson
>
>Maybe I'm dense but isn't that that pretty much the intended
>application for HCT parts?
>specified in the datasheet down to much extra current consumption when
>going to limits
>of Vi and Vcc
>
>-Lasse

"HCT" parts were designed to receive signals from TTL parts also
operating at VDD=5V.

The shifted threshold was done to minimize timing skew when making the
translation.

Over time they've come to be misused as logic level translators, even
though there are specific parts for such purposes.

Unfortunately many lurkers here presume that "getting away with it" is
good engineering practice :-(

Me, I have to deliver good stuff every time... otherwise I'm
unemployed.

                                        ...Jim Thompson
-- 
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Alison wrote:
> Mike Monett <No@email.adr> wrote in message
> news:Xns988770837D9B4Noemailadr@208.49.80.251...
> >   "Alison" <alison@logicsaysNOSPAM.com> wrote:
> >
> >   > Have a look at this picture to save 1000 words;
> >
> >   I hate to tell you this, but that solderless breadboard is about the
> >   worst thing you could be using. With edge rates of 10ns  and periods
> >
> >   I hope this helps. If you need any more information, please ask.
> >
> >   Regards,
> >
> >   Mike Monett
> >
> >   Antiviral, Antibacterial Silver Solution:
> >    http://silversol.freewebpage.org/index.htm
> >   SPICE Analysis of Crystal Oscillators:
> >    http://silversol.freewebpage.org/spice/xtal/clapp.htm
> >   Noise-Rejecting Wideband Sampler:
> >    http://www3.sympatico.ca/add.automation/sampler/intro.htm
>
>
> Hi Mike,
>
> Thanks for the info.  Reading through now.
>
> I'm going to try and get the circuit onto PCB in the next week or so.  The
> final design will also switchover to TQFP devices.  At the moment it just
> about serves the purpose of providing a base from which I can develop the
> firmware for the chip.
>
> To be honest, I hate breadboard!!  But am not in a position to create PCBs.
> The closest I can do is 0.1" pitch, printing out the circuit, drilling the
> holes through, dalo-ing out the bits I want to keep, and then ferric-ing off
> the rest.  That's just toooooo messy.
>
> Prototype PCBs here in the UK are still astromonically expensive compared to
> the US.
>
> Thanks again,
>
> Alison

look at olimex.com they are pretty cheap, 160x100mm two layer pcb with
solderstop 
and silk for something like 33$  

-Lasse

The venerable Alison etched in runes:

.
.
.
> Prototype PCBs here in the UK are still astromonically expensive
> compared to the US.
> 
> Thanks again,
> 
> Alison


Not at all. Have a look here:

 http://www.thepcbshop.com/ 

and go to the 'Plot & Go' service. They'll do one-off prototypes very
cheap and good quality too.

-- 
John B