TPS2350: Output power fluctuating with DC-DC supplies

Part Number: TPS2350

We are using TPS2350 in one of our designs .

In 3 of the 4 boards it is working fine, but one of the board is working fine when input is -48 V from AC-DC Supply but its output is fluctuating when DC-DC supply is used at input.

When connecting both AC-DC and DC-DC supplies it is working fine (giving -48V Output).

While probing pins of the IC in faulty board we got following results- 

-48 V at pin 2, -48 V with fluctuations at pin 6 and pin 11, and -22 V WITH MAJOR FLUCTUATIONS at pin 13

While probing pins of the IC in WORKING board we got following results- 

0 V at pin 2, -38 V at pin 6 and pin 11, and -48 V at pin 13

 Attached is the snapshot of our design

Regards,

Hammad

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