[sdiy] 3.3V regulator ?

[Colin Hinz]

On Mon, 9 Feb 2004, Linium wrote:

> Hello,
>
> I need a 3.3v regulator for a DIR1703 (a spdif->i2s/serial convertor made by
> Texas Instrument). The problem is i don't find this kind of regulator. The
> circuit board will have this chip and a DAC plus minor parts and that's all.
> The DAC needs 5V, and only the DIR1703 needs 3.3V.
>
> I know this kind of regulator does exist but simply are hard to find, i was
> wondering about alternatives.

I'm really curious about where you've been looking, as 3.3V (or even
2.5V or less!) is the "new 5V" in modern digital electronics. In fact,
aside from moldy old legacy stuff and analog circuits, hardly anything
will work on 5V anymore.

> Given that the DIR1703 needs around 50mA for its power and that i don't need
> top notch parts since the DAC will be used for DC signals, can i :
>
> -use a divider bridge with resistors from the 5V power line to make 3.3V
> -use a AOP for the same kind of thing (problem the supply will be 0-5v)
> -use a regulator with variable voltage out, i just discover this possibility,
> there seems to have some regulators that can be "tuned" with a resistor to
> produce a voltage in a given range. I don't know at all if they are good or
> what.

I've used the National Semi LP3961EMP-3.3 with good results. It's got
more current out than you really need, but I'm sure the price differential
is pretty minimal. Be sure to follow the "application hints" with
respect to the filtering capacitors -- they're critical for circuit
stability.

You can also use the National Semi LP2980, which is conveniently rated
for 50 mA -- but the package size is quite small. But so is the DIR1703,
now that I think of it. Again, capacitors are critical.

- Colin Hinz
  Toronto, Canada