TPS2490: Question on SLVA158's SOA calculation

Dear Sir/Madam;

I am a bit confused with the calculation that shown in page 8 (SOA derating example) of the following application note:

SLVA158: “Hotswap Design using TPS2490/91 and MOSFET Transient Thermal Response”

(www.ti.com/.../slva158.pdf

In step 2 with 116degC operating junction temp the derating factor should be 0.393

Taking into this derating factor the device biasing point at 56V @ 1A should already drop outside the boundary of 10ms’s SOA curve.

So I didn’t quite see why in point (3) of the article it still say that “The result is that the device will survive the fault with little margin.”

Thanks.

Chee