FEDEVEL
Platform forum

SkyDvv , 08-14-2024, 03:07 AM

Hey, hope y'all okay.

I just wanted to ask, I don't quite understand something about the chip.
I wanted to design a 20V input to 20V output even in back up.
when vin is connected with 20V i should expect 20V.
when Vin disconnect do i expect that the chip will step up the voltage of the capacitors to 20V?
the explanation in datasheet is quite difficult for me and all the application designs the backup voltage is always less than the VIN.

SirJames , 08-14-2024, 07:41 AM

Yes, LTC3350 will step-up voltage of supercaps up to 35V on Vout when Vin is disconnected or 0V. Set feedback resistors for OUTFB pin according to equation from datasheet (see pic) https://www.analog.com/media/en/technical-documentation/data-sheets/ltc3350.pdf

SirJames , 08-14-2024, 08:07 AM

On page 24, there is also paragraph **Minimum VCAP Voltage in Backup Mode **. Be careful with maximum permitted current of your inductor because low voltage means high current at same output power.