Sometimes its a good idea to just sleep on things....

I probably overstated about the other side of things being sensitive.  On one side is a PIC18F part, and its an LCD module on the other side that requires the 3V (not 3.3V) interface.  So we have the standard 8 bits of data, read, write, enable, etc and so its not high speed, its simply a voltage interface issue.

thanks...moving forward... :-)


--- On Mon, 8/25/08, M. Adam Davis <stienman@gmail.com> wrote:

> From: M. Adam Davis <stienman@gmail.com>
> Subject: Re: [EE] dual voltage translation (resistors vs IC's)
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
> Date: Monday, August 25, 2008, 3:37 PM
> There's a good reason there are few of them - resistors
> are cheaper.
> You'll also find that voltage conversions the other way
> (low to high)
> are generally produced with several convertes in one IC, or
> when the
> conversion isn't as simple as a straight voltage
> conversion (ie,
> isolation requirements, impedance matching, etc).  This is
> because
> converting upwards can be done with a transistor or two -
> cheaper than
> an IC unless you need a lot of them, in which case board
> space may be
> important.
> 
> You could mean a lot of things when you say, "I have a
> sensitive
> circuit on the 3V side" so maybe you can enlighten us
> as to what is
> sensitive about your circuit - are you worried about
> transients,
> overvoltage/current, or something else?
> 
> As long as you meet the specs on both sides of the resistor
> divider, I
> don't see why it shouldn't work without any issues.
>  What are the
> output specs of the driver, and the input specs of the
> receiver?  If
> they are both CMOS chips, they you likely don't need to
> give it a
> second thought - it'll just plain work reliably.
> 
> But if you're really keen on using a chip for it, the
> 4050 was made to
> do this job:
> http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556308;keywords=4050
> 
> It's widely available from many manufacturers. 
> Keywords that will
> help you find other solutions include "Logic
> level" "level converter"
> "inverter" "driver" "3V
> interface"
> 
> Good luck!
> 
> -Adam
> 
> On 8/25/08, alan smith <micro_eng2@yahoo.com> wrote:
> > The other week, the discussion under the topic of the
> iPod serial port, talked about the 5V to 3V interface, and
> of course the use of the voltage divider resistors, R1 in
> series, R2 to ground and where R1=2/3R2.
> >
> > However, just how robust is this?  I know, someplace
> I've seen and used dual voltage translators where you
> can have two independant Vcc and thus go
> > from 5V to 3V (not 3.3) and feel pretty good that
> things are not going to go awry.  Not that I don't
> believe the resistor method works, it does but I have a
> sensitive circuit on the 3V side so I want to look at both
> options but...I can't find the chip(s) that do this. 
> There are several that do a 3.3V to lower voltages but I
> can't seem to lay my hands on the 5V to 3V devices. 
> Looked at Fairchild and NXP,..others?
> >
> >
> >
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