4 Application Cases

A super capacitor is usually used as the energy storage cell in backup power supply systems. The super capacitor is charged when the bus voltage VBUS exists and discharged when the bus voltage falls to hold the VBUS. The lower the boost converter minimum operating voltage, the deeper the super capacitor can be discharged, the longer the backup time. To meet the backup time requirement, the minimum operating voltage is set lower than 2 V but there is no extreme low-voltage boost converter with enough load capability. To optimize the application, the TLV61048 can be used when the VIN pin is supplied by external bias from a buck converter. The details are found in the Smart Meter PLC Module Backup Power Supply Reference Design. Figure 4-1 shows the simplified block diagram of the power structure.

Another case of external bias is for solar panel with only a 0.4V to 0.55V input voltage range. As shown in Figure 4-2, a discrete charge pump circuit outputting 2 × Vout voltage is used to supply the VIN pin after start-up in the Energy Harvesting From Single Cell Solar Panel for Li-Ion Battery Reference Design. The battery voltage is also under the minimum output voltage of the TPS61089 but the system operates well with higher efficiency.