I try to use the LT3757 to step up 48V to 88V in order to driver a 88V led string. I made a simulation in LTspice and it works fine. So i decided to make a prototype based on the circuit's datasheet and formulas as following:
Vcc (chip supply): 12V
Vin(at the inductor): 48V / 8A
When i switch on the circuit, without led string,i can see high output voltage that i can change with the feedback resistor divider. So i adjust the output voltage @ 88V. But, when i connect the led string, the output voltage drops down at 76V with only 10mA in the led string. Adjusting the Vfbx voltage has no effect on the output voltage which stays at 76V and Vfbx stays under 1.6V.
Please, could you help and explain me why i get this issue ?