Maximum Vin voltage specification LT3083

Hi.  The abs. max. ratings for the LT3083 are with respect to OUT, so I highlight that in one of the images below.  

I'm not sure why the reference design on page 28 of the LT3083 datasheet says 28VIN is o.k.  I made some comments on that reference design that I think are appropriate in another of the images below.

There is a reference design in the LT3083 datasheet that can keep IN and VCONTROL within their abs. max. ratings - even at startup when OUT = 0V.  I would try to use the approach used in that reference design to limit the IN to OUT voltages.  

Finally, I show another reference design from the LT3090 datasheet that is another way to limit the abs. max. of IN and VCONTROL.  The LT3090 is a negative LDO, but the idea of using clamps to limit voltages should still work for a positive LDO like the LT3083.

Hello Arad,

Thank you for your reply and information. Based on your feedback I have designed a circuit to limit Vin below 23V when Vout <12V. When Vout >12V than Vin increases to to 27V.

The circuit runs fine, but there is a problem with the P-channel mosfet M2. The GS voltage exceeds 25V. Is there a way to limit the gate voltage on the mosfet?

I think you are a better designer than me but I would just clamp the PMOS S-G with a zener.