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LM5118 question

Other Parts Discussed in Thread: LM5118, CSD18533KCS

Hi all,

I posted earlier with a question about using the LM5118 to charge a 48V battery.

Since that time i have built a circuit using the LM5118 but so far i have been unable to get it to work.

So far all i can get it to do is have the output voltage follow the input voltage (never boosting). the output voltage is exhibiting a saw tooth type shape. the gate signals to the 2 FETs will have some non-zero duty ratio long enough to boost the output just above the input voltage and then both FETS will turn off completely until the capacitor discharges below Vin. Why is it that the controller is behaving such that it works to maintain Vout=Vin? also, once the input voltage gets too high (~35 [V]) the output drops all the way down to under 10 [V]

I have tried using a 12 [V] external bias at VCCX but this has not solved my problem

The schematic of my circuit is below (sorry for rotation, otherwise it was too small too read)

I used the quick-start excel sheet to calculate the values I used

Also, i am using CSD18533KCS MOSFETs in my design right now, could these be the problem?

I have tried using the WEBENCH program but it says that solutions cannot be created unless the output current is dropped to 0.7 [A] is there a reason why i cant output more amperage than this?

ANy help would be appreciated. Thanks guys