I think i am using a fake LM2596. Guessing because it's not from Texas Instruments.

Not necessarily, several other manufacturers make them too. Show a good close up pic of your chip's markings.

 

470 mean 47 with no trailing zeros, i.e. 47 uH.

A 470 uH should be marked 471, meaning 47 with one trailing zero, or 470.

Bob

 

470 mean 47 with no trailing zeros, i.e. 47 uH.

A 470 uH should be marked 471, meaning 47 with one trailing zero, or 470.

Bob

Thank you Bob this is very very helpful!! -

 

Why the 470uH inductor is a problem only when the polarity is reversed, why not during normal operation?

 

you cannot reverse the input polarity, opposite to some posts above, 470uH will work just fine, the only thing that changes is the current ripple is less, which is good for the lower peak current at turn off for the device, 47uH may well be too small.
Check your build, duble check, then check again - most issues are due to build - where did you buy the device from ? there are a lot of fakes out there ....

 

also 220pF on the F/B pin to gnd works well on these chips

 

Not necessarily, several other manufacturers make them too. Show a good close up pic of your chip's markings.

Here's the IC i am using from JLCPCB

 

you cannot reverse the input polarity, opposite to some posts above, 470uH will work just fine, the only thing that changes is the current ripple is less, which is good for the lower peak current at turn off for the device, 47uH may well be too small.
Check your build, duble check, then check again - most issues are due to build - where did you buy the device from ? there are a lot of fakes out there ....

I've had my PCB produced from JLCPCB and all the parts are from JLCPCB as well.

 

Other peoples cock ups are still cock ups ....

 

Hello,

The PCB is showing an inductor with the code 471 , wich is an 470 μH inductor , wich is to large as said before.

Bertus

 

Hello,

The PCB is showing an inductor with the code 471 , wich is an 470 μH inductor , wich is to large as said before.

Bertus

Yes but i am still confused about why when i connect the battery right way; i.e., +12V to +12V, it works perfectly without any heating issues but when i connect the battery the wrong way (reverse polarity) i.e., +12V to Gnd, it makes the IC burst ? the explaination would help me a lot in understanding the electronics behind it.

Also before when i was using SS34 diodes instead of SK34A, the PCB had no problem with reverse polarity, even if i kept it for 5 minutes. Now it just destroys within a second.

 

If you connect your car battery to your car the wrong way round - you get plenty of things being destroyed too - correct ?

as said above 470uH is no issue for the choke value - all opinions to the contrary have no valid engineering reasons behind such comments.

 

Peak reverse current of SS34 is 500uA. Peak reverse current of SK34A is 200uA. Maybe that had something to do with it.

 

Peak reverse current of SS34 is 500uA. Peak reverse current of SK34A is 200uA. Maybe that had something to do with it.

Um, no, not remotely connected - the issue has been exposed as the OP connecting the 12V input the WRONG WAY ROUND to the input - so case solved really .

 

Um, no, not remotely connected - the issue has been exposed as the OP connecting the 12V input the WRONG WAY ROUND to the input - so case solved really .

But then is there something wrong with my P channel Mosfet for reverse polarity protection?

 

So it would appear - except there is no reference to this at all in the original post - some thing of an oversight perhaps that you forgot to mention that you were zapping the circuit with reversed input volts in an attempt to test this feature ?
Possibly a good idea to mention all the ways you were abusing the converter next time.

 

hi nishant,
How is the MOSFET circuit clip connected to the LM2596 circuitry.?
E

 

So it would appear - except there is no reference to this at all in the original post - some thing of an oversight perhaps that you forgot to mention that you were zapping the circuit with reversed input volts in an attempt to test this feature ?
Possibly a good idea to mention all the ways you were abusing the converter next time.

Yes, I'm sorry i forgot to mention that in my original post. But, now that it's out there, could you please tell me how my reverse polarity protection circuit is bad because before that i used a diode (SS34) and it didn't seem to work as well, that is why i replaced it with a P-Channel Mosfet.

 

hi nishant,
How is the MOSFET circuit clip connected to the LM2596 circuitry.?
E
View attachment 248995

Hi thanks for your comment, the MOSFET's pin2 is connected to the 12V plane through a vias on the top layer which also provides to the input pins of the DC-DC through vias.
Please refer to the pictures in the attachment.

 

perhaps you exceeded the Vgs, or the Vds of the mosfet, perhaps you static damaged it ? there are a myriad ways you could have ruined it - over zealous with a soldering iron ... the list goes on ...