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TM4C123GE6PM: Best Way To Convert 3.3 V Output to 5.5 V Output?

Bob Jennings
Intellectual 360 points
Part Number: TM4C123GE6PM

Hi guys, I'm wanting to use my Tiva Launchpad (TM4C123G) with a 16 bit DAC chip that requires a 5 volt power supply.  The Launchpad outputs a 3.3v power supply.  Any advice on how I can convert that 3.3v power supply of the Lanchpad to 5.5v?  I searched the forum and the closest thread I found was this one.  It suggests using an "external push pull driver".  I did a search on Google for this and it gave me numerous results and left me more confused than before I did the search :)   ...I'm wondering if anyone can suggest a simple DIP style chip (fewer pins the better) that can do this.  Any advice?

  • 0
    Guru 47900 points

    Bob Jennings said:
    ...how I can convert that 3.3v power supply of the Lanchpad to 5.5v?

    You do NOT (really) want to do that!   Changing the LPad's supply from 3V3 to 5V0 will DESTROY your MCU.

    Instead - you want to employ a (likely) multi-bit, voltage level converter IC - which manages the signal flow between MCU & DAC.   (such will "up convert" MCU signals to 5V (for the DAC) and "down convert" DAC signals (for the MCU).   Importantly - you do NOT want to alter the supply voltage to (either) the MCU nor the DAC.   You merely want to provide the proper voltage levels between MCU & DAC communication lines - brought about by their differing "signal voltage" requirements.

    I suspect that a quad channel IC would work - your DAC is likely to communicate via SPI or I2C - both accommodated by a quad (4) channel IC.

    Distributors Digikey and Mouser provide excellent search engines - "Voltage Translator IC" should get you close.

    Most of the newer ICs have shifted to surface mount - I'm unsure if your search will reveal a DIP package.

    As an (eased) alternative - many (modern) DACs operate from the same 3V3 as your MCU - eliminating your requirement for any such, bi-directional - voltage translation.

  • 0 in reply to Bob Jennings
    TI__Guru**** 244400 points
    Hello Bob

    There is a 5V pin on the boosterpack header. Is it really required to be 5.5V. Which DAC device is this?
  • 0 in reply to Amit Ashara
    Intellectual 360 points

    Amit Ashara said:
    Hello Bob

    Which DAC device is this?

    Hi, Amit, the DAC is the MAX541.  Datasheet is here.  I have the TM4C123G working with the MAX5353 12 bit DAC and am now trying to upgrade to MAX's 16 bit DAC, unfortunately it is 5v where the MAX5353 was 3.3v.
  • 0 in reply to Bob Jennings
    Guru 47900 points

    Bob Jennings said:
    Why not?

    Brevity is (sometimes) desirable - but not here!   Why not what?

    Your quote clearly implied you were going to POWER the MCU from 5V - which spells "Instant Death."

  • 0 in reply to Bob Jennings
    TI__Guru**** 244400 points
    Hello Bob

    The 5V comes on the header of the BoosterPack. Can you simply blue wire it to your DAC device?
  • 0 in reply to Amit Ashara
    Guru 47900 points
    Amit,

    I believe that poster has identified the fact that the 3V3 output levels from TM4C (may) prove insufficient to meet the 5V DAC's minimum for signal in High.
  • 0 in reply to cb1
    Intellectual 360 points

    cb1 said:

    Bob Jennings
    ...how I can convert that 3.3v power supply of the Lanchpad to 5.5v?

    Importantly - you do NOT want to alter the supply voltage to (either) the MCU nor the DAC.   You merely want to provide the proper voltage levels between MCU & DAC communication lines

    Ah, yeah, this is what I meant.  I understand how my statement could be interpreted in that I wanted my Launchpad to start emitting a 5v output.  Apologies for not being clearer.  Thanks for the tip on "Voltage Translator IC".  Looking them up now...

  • 0 in reply to cb1
    Intellectual 360 points

    cb1 said:
    Amit,

    I believe that poster has identified the fact that the 3V3 output levels from TM4C (may) prove insufficient to meet the 5V DAC's minimum for signal in High.

    Are you suggesting that the DAC *might* work on the 3.3v output level?  I haven't actually tried because I didn't think this was possible after reviewing the datasheet for the DAC and seeing "VDD = +5V ±5%".

  • 0
    Guru 10570 points
    Bob, you are getting confused between power supply and logic levels

    There are, as you might imagine, no single best method for either task. I will suggest simple methods though with a few advantages.

    First power supply. You need to convert 3V3 to 5V. The easiest way to do that is with a DC/DC converter. Theses come pre-packaged in various power rating but I suspect for your use an isolated 1W DC/DC is a good choice (Sometimes 1W is cheaper than 1/2W, especially in small quantities). The isolation allows more selection and more flexibility.

    To find a suitable device the easiest method is to use digikey's parametric search
    www.digikey.com/.../922

    Select input voltage min 3V and below, max 3.6V and above, fixed 5V output, in stock, active with a through hole package and sort by price with qty 1. They make it really easy for you to narrow down you choice by picking your most important parameters first. For something like 1W DC/DC you often find multiple drop in equivalents.

    Make sure you read the data sheet, you will find recommendations for capacitors on the inputs and outputs and even filter for EMC if that is important.

    Now logic levels, for that I'd choose digital isolators for speed and convenience. Many of those can be powered by either 3V3 or 5V supplies so you get level translation and isolation in a single package.

    www.digikey.com/.../901

    These are getting to be quite inexpensive now and are a lot easier to use than optos.

    Now as to why I see the isolation as an advantage? It means that a number of mistakes you can make in interfacing or even just signal issues may be prevented from damaging your micro even if they damage your interface. As well by using an isolated ground you can reduce the chances of ground loop.

    Robert

    One final side note: It's highly unlikely, bordering on the absurd, that you will get 16 bit accuracy out of that DAC. I suspect that even a 14 bit reference will be an order of magnitude more expensive than the DAC. If 16bit accuracy is your goal you've a lot more work ahead than I've outlined
  • 0 in reply to Bob Jennings
    Guru 47900 points
    Good for you - (knew) that is what you (really) meant.

    Amit's provided the means for you to power your 5V DAC - yet in most cases the 3V3 output level fails to (reliably) register as a logic High for a 5V powered IC. The voltage translators provide robust & foolproof (and bidirectional) solutions to your requirement...
  • 0 in reply to Robert Adsett72
    Guru 10570 points
    Oh and search the bookshelf tag, I've provided references to TI seminar literature on interfacing that are good intros.

    Robert
  • 0 in reply to cb1
    TI__Guru**** 244400 points
    Hello cb1

    Bob Jennings said:
    Hi guys, I'm wanting to use my Tiva Launchpad (TM4C123G) with a 16 bit DAC chip that requires a 5 volt power supply. The Launchpad outputs a 3.3v power supply. Any advice on how I can convert that 3.3v power supply of the Lanchpad to 5.5v?


    The reference in the first post is to the power supply (not to the output as what the title suggests). Bit of a confusion here,

    TXB0106PWR seems a good candidate as it supports both push-pull and open-drain topology,
  • 0 in reply to Amit Ashara
    Guru 10570 points

    I see Amit and cb1 managed to jump in before I finished writing.

    Robert

  • 0 in reply to Robert Adsett72
    Intellectual 360 points

    Robert - Thanks for the very thorough reply.  A couple of replies myself:

    Robert Adsett72 said:
    Bob, you are getting confused between power supply and logic levels

    As far as I know, I thought I was only talking "power supply".  Where did logic levels come in?

    Robert Adsett72 said:
    First power supply. You need to convert 3V3 to 5V. The easiest way to do that is with a DC/DC converter. Theses come pre-packaged in various power rating but I suspect for your use an isolated 1W DC/DC is a good choice (Sometimes 1W is cheaper than 1/2W, especially in small quantities). The isolation allows more selection and more flexibility.   ...To find a suitable device the easiest method is to use digikey's parametric search.

    Super!  This seems to be exactly what I needed.  Thanks for the link and the info!

  • 0 in reply to Robert Adsett72
    Guru 47900 points
    Well - we cannot let you, "HOG Everything!"

    Appears that you (may) have missed Amit's identification of 5V being available upon the LPad - for easy powering of poster's DAC.

    As you note - 16 bit DAC is "fantasy land" - similar to MCU vendor's (promotion) of "Security" w/in a sub 10 (USD) MCU!
  • 0 in reply to Bob Jennings
    Guru 47900 points

    Bob Jennings said:
    As far as I know, I thought I was only talking "power supply".  Where did logic levels come in?

    That would be "moi!"   And it is unlikely that your MCU will robustly signal your 5V DAC!   That is where the "voltage translator" for the COMMUNICATION SIGNALS (only) comes in.

    Read again my writing - the detail is there - the forum activity fast/furious...

  • 0 in reply to Amit Ashara
    Intellectual 360 points

    Amit Ashara said:
    The reference in the first post is to the power supply (not to the output as what the title suggests). Bit of a confusion here,

    Ah, I am sorry.  I did use the term "output" (TWICE) in the title.  I should've used the term "power".  I apologize.  I've tried to edit it but do not seem to have the ability.

    Thank you all for you very insight and incredibly fast replies.  You've been very helpful!

  • 0 in reply to Bob Jennings
    Guru 10570 points

    Bob Jennings said:
    As far as I know, I thought I was only talking "power supply".  Where did logic levels come in?

    Once you have provided 5V to the DAC supply pins the logic level inputs to the DAC are now 5V levels which the TM4C does not provide. Thus you need to translate from the tM4C's 3V3 logic levels to the DAC's 5V logic levels and possible vice versa. 5V tolerant is not the same as 5V compatible. You might be able to get to work using just 3V3 logic levels but you are likely working beyond the tolerance build-up if you do.

    That original thread you referenced was referring to logic levels not power supply. And so do the push-pull references.

    Robert

  • 0 in reply to cb1
    Guru 10570 points

    cb1 said:
    Appears that you (may) have missed Amit's identification of 5V being available upon the LPad - for easy powering of poster's DAC.

    Our posts crossed paths, I was writing as he posted. I did recall the launchpad being 5V powered but I avoided it because it was not isolated and as I recalled it's a USB power source which IIRC correctly can be well below the 4.5V minimum supply level for most 5V devices.

    cb1 said:
    As you note - 16 bit DAC is "fantasy land"

    And it's seldom mentioned just how fantastical it is.

    Robert

    It seems everyone expects 20bit accuracy using a +/- 10% power supply as reference.

  • 0 in reply to Robert Adsett72
    Guru 47900 points

    Robert Adsett72 said:
    It seems everyone expects 20bit accuracy using a +/- 10% power supply as reference.

    Wait a minute - are you suggesting that such is NOT possible - or even likely?   Might (that) cause the (dreaded) scope Voids?

    On a (bit more serious) note - it IS possible to introduce a CLEAN (non USB) external 5V to power the LPad.