which one is better choose for level shifter from 5v to 3.3v

Guest · Posted: Sat Mar 26, 2005 9:59 am

hi,
which one is better choose for level shifter from 5v to 3.3v for MMC?
1) use a 7407 buffer open collector with 2.2k pull up res to 3.3v
2)use voltage divider a 3.3k with 1.8k
3)use two 1n4148 series with a pull down res
thanks

Ttelmah · Guest

You don't make any mention of the sort of speed involved?. For fast operation, use a proper shifter. For low frequency work, any of the circuits you mention would work, or you could also just use a series resistor in the line, with a diode to the 3.3v rail to clamp the signal. Each has differences in the speed it will work. The 7407, is bulky (bigger than a proper shifter), but gives fast 'pull down' edges. The two diodes, give faster rising edges. A proper translator is likely to be much more reliable if the line has to travel any significant distance. If you also need signals to work in the other direction, some of the translators offer bi-directional operation, or combinations of both translations in one package.

Best Wishes

Guest · Posted: Sun Mar 27, 2005 12:07 am

THANKS FOR REPLY.
COULD YOU SEND A SCHEMATIC OF A PROPER SHIFTER?
THANKS.

Yashu · Joined: 08 Oct 2003 Posts: 26

Ttelmah · Guest

Or from Fairchild, the 74VX4245.
Maxim do a whole range (the MAX336 is particularly easy/small).
Most of the logic manufacturers do several. The best choice will depend on the number of bits involved, and local availability. Manufacturers like Texas, are more likely to actually 'have' the part, than companies like Maxim (who seem to love long lead times).
The NC7SZ05, functions just like two gates from a 7407, but with slightly lower 'pull down' voltage, in a smaller package, and for some applications is nice.

Best Wishes

Ttelmah · Guest

Make the Maxim number MAX3376. Saw this after posting.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

To go from 5v CMOS to 3v CMOS, any "LVC" series logic will work.

Go here:
http://focus.ti.com/docs/prod/folders/print/sn74lvc125a.html
Download the data sheet. Read the first page. You can run
the gates from 3.3v or 3.0v (whatever you're using), and apply
5v CMOS levels to the input with no problem.

No "schematic" is required. You just drop in the gate.
If you don't want a non-inverting buffer such as the above,
then use a more simple gate, such as the 74LVC08.
http://focus.ti.com/docs/prod/folders/print/sn74lvc08a.html