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LTM8054 failures

Hi, I've had two (out of a couple dozen) LTM8054's fail recently.  They are being used to convert a 28V input to a 35V output, with a typical load of 0.1A.  The schematic is below:

Because of the BGA package, I can't get to most of the pins, but I can see that Vin is 28V, Vout, Iout, and FB are near ground (0 to 0.25V).  The only pin with activity is RT, which shows a 1V pulse every 85us or so.  On a functional board, Vout and Iout are at 35V, FB is at 1.2V, and RT is at a DC level of about 1V (no pulses).  The LTM8054 had no load during testing, and I confirmed Vout is not shorted to ground.  During normal operation (when the failures occurred), the LTM8054 is just powering some op-amps, which are themselves current limited, so I'm not sure how they could have been damaged.  Has anyone else seen a similar failure?

Thanks,

-Greg