txb0104 pull-ups

Discussion in 'General Electronics Chat' started by Gytis111, May 19, 2013.

  1. Gytis111

    Thread Starter New Member

    Dec 24, 2012
    10
    0
    Hi,

    my question is about voltage level shifting chip(txb0104). The problem is that i want to use external pull-ups with it for sd card interfacing, but the chip seems to have internal resistance of about 6-7k itself (with Vcca and Vccb voltages on and OE connected through 10k resistor to Vcca), so my 50-100k external pull-ups won't work. I bought this "magical" chip to avoid using zesistors voltage divider and now i seem to be getting back to the start. Any suggestions?
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Why do you want to use external pull-ups?
    Go back to square one and tell us what you want to interface to what. It is possible that you don't need voltage translators.
     
  3. Gytis111

    Thread Starter New Member

    Dec 24, 2012
    10
    0
    i'm interfacing atmega16(5v) to sdhc(3,3v, 8Gb, kingston). External pull-up would be for ss, mosi and miso lines, sck without. I added an example scheme.
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Why not just power the ATmega16 at 3.3V?
     
  5. Gytis111

    Thread Starter New Member

    Dec 24, 2012
    10
    0
    Because i want to learn it with level shifting, when i'll be over with this, next step will be working with usb, where you cannot escape from 5v. And, also, i put quite a lot of work into this, so definitly won't give up it now.:)
     
  6. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Try simply using current limiting resistors in series with your signals. A resistor of 220Ω should do it. If you are concerned with speed, try as low as 33Ω.
     
    Gytis111 likes this.
  7. Gytis111

    Thread Starter New Member

    Dec 24, 2012
    10
    0
    I think i solved my little problem, it was the placement of pull-ups. I soldered them between sd card and txb0104 instead of between mega16 and txb0104, like it should be. Just didn't pay attention.
     
Loading...