UC2845: What is the temperature restrict reason for different devices?

Hi expert,

The UC184x devices are specified for operation from –55°C to 125°C,

the UC284x series is specified for operation from –40°C to 85°C,

and the UC384x series is specified for operation from 0°C to 70°C.

My customer want to know the reason of the difference, since the Tj is all 150°C, and the thermal information share the same table.

BR

Emma