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 [noparse]:([/noparse]

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, 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 )

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. It's rated at 500mA and has reverse polatriy protection built in. Be sure to read the specs regarding the output cap

-Phil