Re: [ts-7000] Re: 3.3V 5V ideas

Hey Dave,
What's wrong with the simple Open Collector level  shift idea? You have access to the 3.3 supply on the DIO as I recall.. just wondering what you're thinking is there.

--- On Wed, 12/16/09, David Hawkins <> wrote:

From: David Hawkins <>
Subject: Re: [ts-7000] Re: 3.3V 5V ideas
To:
Date: Wednesday, December 16, 2009, 5:53 PM

 

Hi Craig,

> Thanks super for the detailed post, David (and for the tip, Mike)
>
>> Fairchild and TI have many parts that'll work. I'll often
>> use TinyLogic parts from Fairchild as I can scatter the
>> bits around where ever I need them (makes layout dead easy),
>> and they're tolerant to voltages up to 6V.
>
> Would you be so kind as to give me a couple of part numbers so that I can check out the specs?

How about circuit examples instead:

http://www.ovro. caltech.edu/ ~dwh/carma_ board/gda06rb004 _carma_v0. 87_dec03. pdf

p12 U38 NC7SZ125P5X tri-state buffer.
- 3.3V pull-ups on the input also route to a 3.3V FPGA.
- the output is pulled up to 5.5V
- the buffer protects the 3.3V FPGA

p12 U100 NC7SZ125P5X
- buffered signal to increase current drive to multiple loads

p13 U62 NC7SZ384P5X
- bus-switch
- 5V or 3.3V signal to 3.3V signal level bidirectional level
shifting
- the bus switches are disabled until the board power is
good

There's a bunch of other parts in there too.

Pericom, TI and Fairchild also have LPT and LCX series parts,
and I believe they're 3.3V powered, but 5V tolerant.
You can use their parametric searches to figure that out.

> I've hand soldered SMT devices to boards, but you describe
> a technique that I haven't used--"use a flux pen to wet
> solder wick and use that to remove the excess solder from
> the pins". That sounds really clever--how exactly to you
> "wet solder wick?" I've been trying to be so compulsive,
> this may help my sanity ;)

Using a flux pen (looks like big an indelible ink marker,
or yellow highlighter pen) you physically dab the pen
on the wick (the copper braided stuff, make sure to
use a thin version), and then its wet.

Now when you touch the soldering iron to the wick, which
is in turn pressed into your horror of a soldering job,
the solder reflows into the wick, leaving just enough
on the pins to keep the part happy, but the shorts at
bay :)

>> Even knowing about solder-mount pads, I would generally
>> not use them anymore. I find it much simpler to layout
>> a simple PCB with headers, and whatever power-sources
>> I decide to put on it.
>>
>> Check out http://www.barebone spcb.com
>
> Thanks, David. I use gEDA and have fab houses build the
> boards, but I've been so into the whole breadboard it all
> up first concept that I hadn't really thought how cost
> effective it would be to hybrid breadboard/circuit fab.
> What a great idea.

Its so much nicer to have a bunch of little PCBs with
serial translators with DB9s and headers etc lying around
than it is to have veroboard monstrocities :)

Cheers,
Dave

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