The LTC3355 is a complete input power interrupt ride-through DC/DC system. The part charges a supercapacitor while delivering load current to VOUT, and uses energy from the supercapacitor to provide continuous VOUT backup power when VIN power is lost. The LTC3355 contains a nonsynchronous constant frequency current mode monolithic 1A buck switching regulator to provide a 2.7V to 5V regulated output voltage from an input supply of up to 20V.
A 1A programmable CC/CV linear charger charges the supercapacitor from VOUT. When the VIN supply drops below the PFI threshold, the devices's constant frequency nonsynchronous current mode 5A boost switching regulator delivers power from the supercapacitor to VOUT. A thermal regulation loop maximizes charge current while limiting the die temperature to 110°C. The IC has boost, charger and VIN programmable current limits. The LTC3355 is available in a 20-lead 4mm × 4mm QFN surface mount package.
Demonstration circuit 2040A is a 12V to 4V/1A regulator with an integrated supercap charger and backup boost regulator featuring the LTC3355EUF. The LTC3355 charges up a 3F supercapacitor from the output when the 12V input is available. When the 12V input fails, the backup boost regulator supplies the output until the energy in the supercapacitor is depleted. Figure 2 illustrates how long a 3F supercapacitor can provide a 4W output when the input power fails (~600ms).