Voltage regulator reading high

[camerart]

Hi,
I've just built a PCB, with 2x 3.3v voltage regulators. Both of them are reading 4.2V.

This has happened before, but I can't remember what I did to fix it. Does anyone have any ideas please?

Camerart.

 

[Nigel Goodwin]

Are they oscillating?, do you have suitable capacitors placed correctly?, and a suitable load?.

 

[KeepItSimpleStupid]

Check layout pin assignments. Minimum load requirement. Oscillations (Bypass cap). Agree with Nigel.

 

[camerart]

Hi N and K,

I have previous circuits wired the same way.
I tried removing the caps and replacing them 4.2v both times.
There are two REGs on the PCB.
There is a PIC connected. to one of them, both still 4.2V
C.

 

[camerart]

Hi,
I've found the problem!

I looked more closely at e numbers on the regulators, and the offending ones are ON RFE 17L50 where previously I've used ON RGH 17-33 I've changed them and now they both read 3.3V

Does anyone have a data sheet for ON RFE 17L50 please, I think they must have a different pin out arrangement. WHY !!!

Thanks, C.

 

[Nigel Goodwin]

Does anyone have a data sheet for ON RFE 17L50 please, I think they must have a different pin out arrangement. WHY !!!

Going from the number aren't those 5V regulators? - what's your source voltage?.

 

[tomizett]

Can't find any datasheets matching 17L50.... does sound like it could be a 5V though.
Regarding pinning, however, you'll find that some regulators - even in the same package - do have different pinning. The difference (in my experience) is between "standard" dropout regulators, which use an NPN pass transistor, and "low" dropout regulators, which use a PNP pass transistor. I presume it's to do with which terminal of the pass transistor needs to be bonded to the thermal tab - although that said, in a standard +ve regulator the tab is ground, which is not one of the pass element's terminals at all...

So the moral of the story is to check the pinouts for the exact device you're using - take it from someone who cam close to being caught out by this recently!

 

[camerart]

Hi N and T,

I'm sure your correct and they are 5V regs (5V Battery = 4.2V). (Just had another look at the component tube and sure enough they're marked 5V AND! I've drawn the pinouts on the tube, which are the same)

Cheers, Camerart.

 

[camerart]

Can't find any datasheets matching 17L50.... does sound like it could be a 5V though.

Hi again T,

I requested the D/S from 'ON' and they said use LDO NCP117LPS50T39.Thanks for looking

C.