Torex published a new technical information document 0029, which introduces a method to parallel two supplies (the main board supply and a Li-Ion battery) to power a single output. While the Li-Ion battery is not in use, it will get recharged by sampling a small portion of the current from the main board supply.
The document describes a circuit that splits power between a main board supply and a Li‑Ion battery to drive a single output. It details the roles of the XC6227 LDO regulator, the XC6802 battery charger, and the XC9135M step‑up converter, and references TIP No.28 for background.
Three operating cases are covered: (A) both supplies active with the main supply higher, (B) main supply voltage dropping below the battery‑derived output, and (C) main supply disconnected, where the XC9135M alone powers the output. Key design points such as charging‑current setting, LDO dropout voltage, and UVLO thresholds are also discussed.
| XC6227 | LDO voltage regulator with built‑in reverse current protection |
|---|---|
| R_SEN | Resistor that sets the maximum charging current for the XC6802 |
It is set by the resistor R_SEN, which determines the maximum current the XC6802 can draw from the main board supply.