• Accept power from a solar panel, a 1S LiPo battery, and USB input
• Charge the battery when an external source is available
• Power the system from the battery when no external source is present
• Generate regulated output rails of 12 V, 5 V, and 3.3 V
• Prioritize USB input over solar input when both are connected

• Accept energy from a 6 W solar panel
• Accept power from a USB-C receptacle
• Interface with a 1S LiPo battery
• Manage battery charging from available external sources
• Provide regulated output rails for downstream electronics
• Enforce source prioritization so USB overrides solar when both are present
• Keep the 3.3 V rail available whenever any valid source exists
• Provide either 5 V or 12 V from a selectable boosted rail, one at a time

• Battery shall charge when solar or USB is connected and sufficient source power is available.
• Battery shall power the system when no external source is available.
• When external power is present, external power should run the system and recharge the battery.
• If external power is insufficient for both load and charging, maintaining system operation takes priority and charging current shall be reduced or deprioritized.
• If both USB and solar are connected, USB shall be the active source and solar shall be prevented from supplying power.

1. External power sources: solar input and USB-C input
2. Source qualification and prioritization stage
3. Battery charging stage for the 1S LiPo battery
4. System power-path / load-sharing stage
5. 3.3 V rail generation stage
6. Selectable boosted output stage producing either 5 V or 12 V
7. Output distribution stage for downstream loads

• Ideal-diode OR-ing with explicit priority control
• PFET-based power-path selection
• Load-switch or power-mux style selection

• USB has priority over solar.
• Solar does not need to be physically disconnected.
• Solar must simply be prevented from contributing power while USB is present.
• External power should operate the system directly when available.

• Solar input
• USB-C input

• Use CN3063 as the initial preferred LiPo charging controller.
• Favor safe, conservative charging behavior rather than aggressive fast charging.
• Respect the USB input current budget.
• Allow solar charging whenever the solar source is available and above a defined usable threshold.
• Ensure charging current can be reduced or suspended when external power is insufficient for both charging and load operation.

• Generate the 3.3 V rail using RT8059 as the preferred starting point.
• Support 500 mA continuous load, with some additional peak margin.
• Keep 3.3 V available whenever any valid source exists.

• Confirm suitability over the full system input range.
• Confirm expected efficiency across the battery voltage range.
• Confirm ripple, transient, and thermal behavior against downstream needs.

• Use MT3608L as the preferred starting point.
• Generate either 5 V or 12 V, selected manually, one at a time.
• Prefer a manual switch rather than a jumper.
• Ideally support output selection while the board is powered.

• Final selection topology
• Whether live switching requires output blanking, discharge, soft-transition, or interlock behavior
• Whether MT3608L is still the best fit after architecture review

• 5 V and 12 V are not required simultaneously.
• 3.3 V should remain available regardless of whether 5 V or 12 V is selected.

• The listed outputs should be treated as continuous worst-case loads.
• Additional margin should be allowed for peak current events.
• The 5 V and 12 V rails are selectable, one at a time, which reduces the worst-case boosted-load burden versus a simultaneous-output design.
• USB input budget of 500 mA is likely to be a major system constraint during charge-plus-load operation.
• Solar performance cannot be budgeted accurately from Voc alone.
• Converter efficiency will strongly affect battery runtime and thermal performance.

• Worst-case battery input current in each operating mode
• Worst-case USB current draw during load plus charging
• Realistic solar contribution under non-ideal conditions
• Conversion losses for the 3.3 V and boosted rail
• Runtime with 4400 mAh battery for representative load cases
• Thermal dissipation in charger, boost, buck, and priority path elements

• The LiPo battery is a single-cell chemistry with nominal voltage near 3.7 V and full-charge voltage of 4.2 V.
• The board is intended for indoor use.
• USB is the highest-priority external source whenever connected.
• 5 V and 12 V are mutually exclusive outputs.
• 3.3 V must remain available whenever any valid source exists.
• The project is currently in architecture/specification phase only; no schematic decisions are yet locked.

• Solar input is variable and environment-dependent.
• USB input budget is limited to 500 mA.
• Battery voltage varies across charge and discharge states.
• One boosted rail must serve two output-voltage targets, implying mode selection and non-simultaneous operation.
• The design should remain appropriate for a low-power indoor embedded application.

• Exact USB-C implementation scope
• Solar qualification threshold and real operating point assumptions
• Acceptable transient behavior during live 5 V / 12 V switching
• Downstream rail quality and startup expectations
• Preliminary operating-mode power budget