SPV1040 Failure

[Pramod_Bangalore]

we are noticing some failure SPV1040 in our implementation on a board for energy harvesting from solar panel. The breakdown is only for SPV1040. Short between GND and Vout. Attached schematic for your reference.
we have taken the reference design of STEVAL-ISV012V1 and gone through the design recommendation doc of SPV1040. 

@ peter Bensch  
Can you please check and suggest on design.

Need support ASAP.

[Hexel]

There`s actually couple of designs available with PCB.

https://docs.rs-online.com/c85f/A700000006572356.pdf

https://www.farnell.com/datasheets/1817171.pdf

https://static5.arrow.com/pdfs/2012/1/1/0/33/7/806/st_/auto/cd00292052.pdf

Both have supercap at the 1040 output so my assumption about trantient overvoltage may be correct. Following your symptoms that fail occur at high input and light load condition, lower FET may fail suddenly due to overvoltage when IC goes into constant-voltage regulation mode. MPPT loop response may be to long to hold voltage within acceptable limit. Supercap will provide sufficient time for loop to control voltage. Even while TVS is populated, its trim voltage lies far above IC failure threshold of 5.5V. And with use of supercap, shunt is absolutelly required to limit IC current.

Here`s another advice: you may debug PCB from a bench PSU in lab, just set its voltage and current to limiting ones of PV, I think it will ease you work.

[Pramod_Bangalore]

we have tested with 220uF in C6. still we are seeing failure in spv1040. failed after 4 days, battery is 4.14 V at the time of failure.

Note - we have connected our system power parallel to battery. (on average it can consume max 350 mA while triggered else it will consume 20mA )

Specification of solar panel - 3.85V/4.4W, Voc:4.55v,Vm:3.85v,Isc:1.22A,Im:1.14A

[Pramod_Bangalore]

we have limited the charging current to 250 mA  from L6925D IC but still we are facing failure in SPV1040. Battery volt at the time of failure 4.1V.

@Peter BENSCH @Hexel  any suggestions or help please. 
@Peter BENSCH we are near to the production please look into it.

[Hexel]

Run setup in a lab, use bench PSU to mimic PV behaviour (set PV limiting parameters as curr and volt of PSU). Check if 1040 tracks PSU settings and runs around that point (PSU mode will switch countiniously between CC CV mode). Manually charge battery to voltage of interest and take maesurements of key points: waveforms of input current (drawn from PSU), LX, VOUT voltages. It all could be done in lab and is a basic diagnostic jobs to talk about. I`ve already asked to put these waveforms here to take a look at. Show you PCB design, screenshot by a layer will be enought.

And you probably missed that supercap is not a 220uF (microfarads) but 220mF (millifarads). 3 orders difference BTW