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Interfacing 3.V and 5V TTL

Hari T O0
Genius 3820 points

Hi,

I want to interface two TTL IC's,in that assume one is working at 3,3V and the other is working at 5V.

Do I need to use a voltage level translator IC?. If yes why if no why.Please reply.

Thanks&Regards

Hari T O

  • 0
    Guru 316380 points

    TTL always means 5 V. There is a standard called LVTTL for 3.3 V devices, which uses exactly the same thresholds as TTL.

    Some people mistakenly use "TTL" to describe CMOS ICs, which can be incompatible with actual TTL ICs at the same supply voltage.

    So unfortunately the word "TTL" contains no information at all. Specify the exact IC model, and its properties, and in which direction the signals go in your circuit.

  • 0 in reply to Clemens Ladisch
    Genius 3820 points
    Hi Clemens,
    Than you very much.It was an interview question asked to me.They just asked that is it possible to interface two TTL IC's which are working at 5V and 3.3V.
    I have one more question,imagine we want to interface a flash memory to a microcontroller.what are the analyses do we need to do before we say "OK this IC can be interfaced with this microcontroller".I usually do a comparison of their Voh,Vih min and max levels. Do we nned to check anything more than this
  • 0 in reply to Hari T O0
    Guru 316380 points
    Other possible considerations are speed, current (i.e., drive strength), and interface (I²C/SPI/whatever).