Is it possible for the LT3081 to generate 40V from 45Vin if the potential difference from Vin to Vout is within 40V?

Hi,
be aware that "absolute maximum ratings" are not intended for steady use.
If the input voltage range is stated as maximum 36V, you will probably damage the device with 45Vin.
Also keep in mind that if there is an unintentional short of Output or just after power-up, Uout ->0V - hence destroying the IC.

Hi　Alexxx 

Thank you for the reply.

I have more question.

What is the absolute maximum rating of the IN pin from GND?
And what is the absolute maximum rating from GND of the OUT pin?

Best regards

Hi.  The LT3081 is capable of arbitrarily high output voltages, but as Alexxx mentions, you need to be careful about start up and faults.  We don't have a reference design of arbitrarily high output voltages for the LT3081, but the LT3090 datasheet has a reference design that shows the idea and I show that in the image below.  The LT3090 is a negative LDO and has a GND in that can attach to OUT, but the same idea of clamping with zeners can be applied to the LT3081 with no GND pin.