LT3796 as capacitor charger

I'm trying to use the LT3796 as a boost regulator (12-30 in, 45V out) to charge a capacitor bank, but my LTSpice simulation shows the device is in a fault condition and it never toggles the Gate output.

As a sanity check I modified the example simulation, LT3796_TA01A.asc and isolated the problem. As soon as I remove the LED from the circuit and connect straight to GND, the fault appears. I guess this makes sense, as the inrush of Vin (through the inductor and the Schottky diode) is racing through to ground and creating what looks like a short circuit regardless of the state of the rest of the chip.

So, I'm guessing this is more of a topology problem. Is there a way to do what I want, to use the LT3796 to charge caps from 0V up to the CV limit at constant current? SEPIC?

Thank you,



  • 0
    •  Analog Employees 
    on Dec 2, 2020 2:01 AM 4 months ago

    Hi Brian,

    Yes, when you tie the ISN to ground, the circuit will see a shorted output. You must connect your load from ISN to GND to operate. I have tried placing a load (212 Ohm) from ISN to GND and the Gate started switching. You can try simulating with your load tied to the same pin I mentioned.

    For simple operation, boost converter is enough for your needs since your input voltage range is below your target output voltage.