problem in getting native voltage using NCP3170

[manju_gowda]

Hi,
I have conducted test to obtain -5V using NCP3170 as explained in a link https://www.onsemi.com/pub_link/Collateral/DN05004-D.PDF (Figure 1)
In case 1: with input voltage 5V and without any output load I was able to get -5V .
In case 2: with 5V, and later test with 8V input voltage, if i place a load of 15 ohm or 100 ohm across the output I'm not getting the -5V, and the chip does not turn on switching. Instead I'm getting +2V or 0V. Changing the chip twice times yields the same result.



Please suggest potential causes and solutions to this problem.

 

[alec_t]

Double-check that you have a good connection to pin6 (Enable). Is your circuit built on a breadboard or a pcb?

 

[manju_gowda]

enable pin is high thats sure . and i did this circuit on general pcb board

 

[cowboybob]

I think that, in this case, your load resistances are too low.

Try increasing the output load resistance (gradually) and see where the SMPS starts switching, giving you the negative output you expect.

I believe this circuit is only for providing a negative "rail" (or potential) of little current capability: something you might use to assure that, for instance, and OpAmp comparator circuit output goes all the way to zero volts (or less) when appropriate.

On that note, there are simpler circuits for that purpose...