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TPS23861: TPS23861's Particular Batch has a High Failure Rate?

yang qing
Prodigy 10 points
Part Number: TPS23861

Hi,

 

We have a problem with TPS23861 chipset. We have been using this chipset in our project under normal environmental temperature. After 24 hours of continuous running, about 2.5% of our entire batch of 1000 pcs would exhibit failure. The PoE would not be able to detect our PD device and supply electricity to our board.

 

We initially thought that it might be due to a huge spike or fluctuations on the 48V that caused the chipset to fail. Therefore, we added a lot of protective circuits including adding a 510-ohm resistor on the 48V, as well as adding a protective transistor and some capacitors. However, this does not reduce the failure rate of this chipset on our board.

 

Attached is our Schematic for the PSE and the step-up voltage circuit:

1.      External supply of 27V. We stepped up to 48V through DCDC boost.

2.      We controlled TPS23861’s I2C and Reset through the MPU. MPU’s IO Voltage is 2.62V.

 

This is our schematic:

 

 

When we used an oscilloscope to test Drain1 to Drain4, we are unable to see any detection signal that is supposed to be there (as illustrated in the picture below):

 

(We could not see any of these detection signals. Our signal is always one straight line)

 

We have also done some comparison on the registers of the spoilt and normal chipset and discovered that for all the spoilt chipsets, they have the same “Firmware Revision” (0x41)and “Silicon Revision Number”(0x43). The normal chipset does not have this “Firmware Revision” or “Silicon Revision Number”. This seems to imply that this particular batch of chipsets with this “Firmware Revision” or “Silicon Revision Number” is more susceptible to failure, but we cannot be absolutely sure. We also do not know if these parameters have been re-written after it is spoilt, though from our understanding, these 2 registers are not writable. 

 

Normal Chipset Register Dump

 

Spoilt Chipset Register Dump

 

We have analyzed the spoilt chipset as well, and do not see any shorted circuits or anything that is abnormal.

 

Currently, we are at a loss. Can somebody advise us on what to do next?