ldo regulator question

[s2jesse]

http://www.national.com/ds/LM/LM1117.pdf

so im looking at using this regulator...
the 3.3V fixed output version
sot-223

i see 4 pins....

Input
Output
ADJ/GND
and VOUT


input is the input obviously which will be·5v·im getting this from rc reciver
ADJ / grnd obviously ground
what pin will be the 3.3 out· the output or the Vout

I dont have the part so cant test it but trying to layout· a board right now.

With say a 7805 there is just gnd, input, and output, but based on the this regulator the datasheet leads me to believe i should use the vout instead of the output... im confused :(

any tips woudl be appricated so i can add the caps and finish up the board design.

Thanks Jesse




·

[Luis Digital]

Pin configuration:

SOT-223

1- GND
2- VOut (Large pin is also VO)
3- VIn

At first I used the variable version with excellent results (and also LM317), but one must add two resistances. Now I have LD1117S33TR (http://www.luisdigital.com/tienda/product_info.php?products_id=37), for the Propeller and to repair monitors LCD.

[pems]

if you plan to feed only 5v, i'd think you need to use something called a "very low dropout" linear regulator. One i am successfully using for 5v->3.3v regulation is this one: LD29080DT33R from ST (free samples are available http://forums.parallax.com/images/smilies/smilewinkgrin.gif )

[s2jesse]

thanks guys...

according to what i can make out on the specs its seems the drop out voltage is about 1.2 would should be fine for 5 volts i would think no? ill check out the st regulator thought now.

[s2jesse]

Ahh ok nice the ld2908 seems to have less than half the drop out voltage nice thanks for the pointer.

[Phil Pilgrim (PhiPi)]

Also take a look at the LM2937IMP-3.3 (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM2937IMP-3.3CT-ND). It's rated at 500mA and has reverse polatriy protection built in. Be sure to read the specs regarding the output cap

-Phil