Defect INN2604 units
Dear sir or madam,
we are utilising the INN2604 in one of our power supply designs. This power supply is in production for 4+ years already without notable difficulties.
This summer we recieved a customer complaint, where multiple units (>30) fail to deliver power after circa one year in the field. Our product is used in a IT / data center application. Input power is universal 100V-240Vac. Our customer states the whole installation is sourced by a online uninterruptable power supply (UPS).
The load itself appears to be fine. Supplied with an external lab bench power supply the current draw is fine and there is no short circuit. But there are defect components on the secondary side (e.g. rectifier diode - parallel to the SR MOSFET)
I have five units with me. I check the drain-source voltage Vds of the INN2604 internal MOSFET. The MOSFET is turned off and the measurement shows the rectified and filtered 325Vdc, as to be expected with 230Vac RMS line voltage.
There is no "sign of life". The converter will not start switching.
I check the Input Voltage Monitor pin. It is about 12V, which is too high. Counter-check with a "healthy" unit there are about 4V, which is fine.
I disable the Input Voltage Monitor (V) pin and tie it to the Primary Bypass (BPP) pin. This net now measures 0V (BPP vs. Source/Primary GND).
I tried to supply 5.95V via an external power supply directly to the primary BPP pin. The lab bench power supply enters current limitation (> 100mA), the pin appears to be shorted to ground.
I checked the RCD snubber circuit. All the parts, which I previously desoldered from the board, are intact and have their nominal values.
Furthermore, I tried to change the IC itself. On the backside a hole in the enclosure revealed itself. It is located in proximity to the drain and source pin. Please find pictures attached to this post. The desoldering itself is not the issue, because I have another unit where the INN2604 is still on the board and you can see the same bit of molten enclosure.
What conclusions can be drawn? What might have caused the damage of the INN2604 converter IC?
Is there any possiblity to investigate this further?