The cause of LT8491 generation of heat

Question

I made an evaluation board with LT8491 by myself. It works, but it is hot very much. I'm searching the cause of this heat. Not the whole surface but the side of 33pin-52pin gererates heat, about 70 degree with 3 minutes. This is saturated. It's same as both with-load and without-load. The circuit is blow. I changed the FETs in red circle to the more drain current. 
 Could you give me some advices to solve ?

EZAutoReply · Accepted Answer

The LT8491 has an internal LDO. If both the input voltage and output voltage are high, the LDO must step down to the internal voltage and will dissipate a lot of heat. Try supplying EXTVCC with a separate supply set at 8V to 10V and see if that makes the heating acceptable. Also, ensure the MOSFETs you are using do not require a very large gate charge.)

EZAutoReply · Answer

Yes, with the internal LDO having to step down from either 50V or 56.8V, the IC will get hot and 100C sounds reasonable. If you use a small internal buck supply feeding EXTVCC set at 8V to 10V, it will run much cooler. This buck supply could be powered from the input supply to minimize drain on the load battery. Powering the buck from the PV panel is also beneficial as you stated if the load battery is removed. You could also diode or the PV panel and load battery to the buck supply so it always has power if desired. Keep in mind, if EXTVCC voltage is not present the LT8491 will take power from the Vin pin.

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The cause of LT8491 generation of heat