View Full Version : ldo regulator question

01-16-2009, 09:56 AM

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

i see 4 pins....

and VOUT

input is the input obviously which will beˇ5vˇim getting this from rc reciver
ADJ / grnd obviously ground
what pin will be the 3.3 outˇ the output or the Vout

I dont have the part so cant test it but trying to layoutˇ 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
01-16-2009, 10:29 AM
Pin configuration:


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.

01-16-2009, 11:58 AM
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 )

01-16-2009, 02:17 PM
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.

01-16-2009, 02:24 PM
Ahh ok nice the ld2908 seems to have less than half the drop out voltage nice thanks for the pointer.

Phil Pilgrim (PhiPi)
01-16-2009, 02:59 PM
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