Level translation 3V to 5V and 5V to 3V

Hans Wedemeyer · Joined: 15 Sep 2003 Posts: 226

A new project requires the PIC to run at 5V and Bluetooth at 3.3 V. I will need a 5V to 3V and a 3V to 5V conversion.

Data rate will be about 230,400bps

Anyone have a favorite chip that is available to the general public ?

I like the look of MAXIM 3370 however minimum quantity 2500pcs !

MAX1840 and 1740 are also interesting, just the same old same old... MAXIM parts are hard to get.

Please don't suggest resistors etc. I do not want to design a level shifter.

This has to be done right and needs to be small.

valemike · Guest

There are some newly advertised PICs out there now that can run at 3.3V and still run at high frequencies. Then you can run all of them at consistent 3.3V.

I too am looking for a dual output voltage regulator that I can run off a 9V battery. Need one at 3.3V and one at an adjustable 5V-6V

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

You can also use a 74HCT08 as well.

Hans Wedemeyer · Joined: 15 Sep 2003 Posts: 226

The single gate versions are what I'm looking for.
They are also available from Digikey....
I appreciate the help.

Starting yet another Bluetooth project.

When the PIC side of it is done it requires a program for the iPAQ and a PC (laptop). I've just finished studying the SPP RFCOMM using WinSock.

I must say after all those years of wired RS-232 Bluetooth makes life much easier, and once the learning curve is done with the PC side of it, it just works that much better.
Tests I ran yesterday had data streaming at 352kbps on two devices and I never used the audio channels.

kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley

If I'm not mistaken, PIC18F and PIC18LF series can run on 3.3V.

If you can not buy Maxim chips for money, you can get them as free samples.

Nick

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

His problem is not samples. He doesn't want to trapped by Maxim,
wherein Maxim says parts are in production, then you design them in
and prototype your board, and then your purchasing department finds
that no stock exists at Maxim. Then, if you're lucky, and if you have
a really good purchasing dept., they search around through back
channels and friends, and maybe find a few tubes somewhere so you
can ship your product.

Then, having learned your lesson, you never let this happen again.

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

If the I/O, on your PICC, is going to be uni-directional and not needing to change directions then a simple voltage divider could work (going from 5v to 3v). There is really no need to convert from 3v to 5v since the High of the 3v device should be higher than the minimum voltage required to make the input, of the 5v device, see a high. If your PICC needs to be bi-directional then another IC is needed.

Ronald

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Yes, but he said he didn't want to use resistors. It's true that if he
uses a port that has TTL inputs (typically port B), then he doesn't
need the level shifter from the 3v device, but a TTL port may not be
available. Also, he may be using the SPI pins on the PIC to talk to the
Bluetooth device. The SDI pin on the PIC is a Schmitt Trigger input,
which has a Vih of .7 x Vdd (3.5v), which is higher than the 3.3v device
can provide. So a 3.3v -> 5v level shifter is needed.

Wilhelm · Joined: 04 Jun 2005 Posts: 4 Location: Namibia

I had a similar problem when I was trying to get USB to PIC comms.

I Found the TUSB3410 (req 3.3V) and PIC's and the P82B715PN I2C Bus extender (5V) didn't work together.

The TUSB3410 is a USB to Serial and I2C chip that I use for all my USB designs. the P82B715PN is a I2C bus extender runing on 5V (So Does my PIC's) and my TUSB is 3.3V.

I used 2x FDV301N (RS #354-4907 or Farnel #995-848) and 2x 10K resistors to do this. (The Gate is on 3.3V, Source is from TUSB and Drain is to the P82B715PN. with a 10K resistor on drain to +5V)

This takes my 3.3V source and gives me a 5V output for my bus extender or PIC. I am sure it can be adaped for other use ?

My reason for the FDV301N is that the speed of the device is enough so it can handle the I2C SDA and SCL without any data problems. (Also VERY tiny ... Smile

)

Hope it helps.

Wilhelm

Hans Wedemeyer · Joined: 15 Sep 2003 Posts: 226

I have to level shift from the PIC(5V) to the Bluetooth(3V) and resistors are not a good idea unless the values are low enough to avoid slew rate problems.

I could use simple fet inverters and double them to get the signal back in phase, but all those components and it can all be done with two SOT23-5

I simply do not want the hassle of worrying about level shifter.
It's somtheing a chip should do. I just want it to work and be simple to assemble.

PCM Programmer is correct about MAXIM. I love the products and will use them when I know I can get them in reasonable time.

Samples are not the issue, when I hand the design over to my client they will have to be able to get the parts. Maxim has leads times of weeks and months.

I use the MAX1674EUA a lot (currenlty have 150pcs) and am happy to see Digikey stocks them now. I tended just to buy them from Maxim in 24 pcs lots because they were sometimes available. !