Hi
I see the reliabilty report (r530) of LT3693.

LT3693
Production
The LT3693 is an adjustable frequency (200kHz to 2.4MHz) monolithic buck switching regulator that accepts input voltages up to 36V. A high efficiency 95mÎ...
Datasheet
LT3693 on Analog.com
Hi
I see the reliabilty report (r530) of LT3693.

Hi N. Kokubo,
Apology for late reply. Just got confirmation from reliability team that 55°C means ambient temperature Ta.
Hi Fil san
Thank you for your answer.
I close this question.
Best regards
N.Kokubo