TPS62736: When Vout is higher than Vin

Hi Kenny,

I do not expect damage as long as VOUT is less than the abs max rating.  However, we haven't tested that condition extensively so I can't warranty that operation.

Regards,

Jeff

Oh, thank you so much for answering me in the Thanks Giving Holiday!

I will appreciate your help if you can be more sure.  Either yes or no is ok.  May be after you go back to work?

Yes or no affects our production procedure.  Because TPS supplies 3.3V to the CPU.  But when we do the on board programming, the program writer also supplies 3.3V to the CPU.  At this moment, Vin of the TPS is 0V, but its Vout gets 3.3V from the writer.  So we are afraid that some TPS may not be strong enough to stand this reverse voltage.  So really need your help to make it clear.

Thank you so much!

Kenny

Hi Kenny,

Since there is a dc path from VOUT and VIN through the inductor and the buck converter's high side FET body diode, VIN could see VOUT=3.3V minus a body diode drop (~0.6V).  I can test one unit at room temp on the bench to see if this causes an issue but I can't test a statistical sample over temp to provide a warranty for the device operated in the this manner.  So, unfortunately, I have to say no.  Can you add a PFET following the TPS62736 VOUT pin with an NFET at its gate that pulls down on when the TPS is not on? 

Regards,

Jeff

Dear Jeff,

Thanks for the answer!  So please help to verify at room temperature is good enough.  Thank you!

And is there any way to get around of the surge current?

The load draws 350 mA for 50 us, and then remains at 30 mA.  

The surge current triggered your short circuit protection.

I added a LC  between TPS and the load, hoping to filter this surge.  But then the TPS output kept on pulsing at 25 kHz.

The C is 400 uF, L was 60 uH.  But it could not filter (but was not pulsing). 

So I put several unknown inductors in series, hoping to be large enough.   Then it was pulsing.  But it could not be stopped by eliminating one by one, until the last one was short.  Sorry to tell you something without figures.  But do wish you can give me some hints to get around of this surge current.

I could use a larger DC DC converter, but I like this one which has the highest efficiency.  I am regulating the power output from your solar energy harverting IC BQ25505.  So every uA counts.  Or if you have a more suitable one for me, please let me know.  Thank you so much!

Kenny

Hi Kenny,

I had to order an EVM so I can't test until Monday.  Can you explain more about the surge current?  I am assuming it is from the load on VOUT?  

Regards,
jeff

Dear Jeff,

Yes, the surge current is drawn by the load on Vout.  350 mA for 50 us.  Then stays at 30 mA.

I want to attach some drawings to help the explanation.  However, I don't know how to attach it.  Sorry!

Thank you for your help and looking forward to hearing from you soon!

Kenny