Design Specification Development

flux

I updated the living spec to a v2 in Design Specification.
What changed:
  • Locked in USB-C, 500 mA USB budget, 1S 4400 mAh LiPo, and onboard battery protection
  • Recorded that external power should run the system first, with charging as secondary when source power is limited
  • Locked in USB priority over solar, with solar allowed to stay attached but not contribute when USB is present
  • Locked in always-on 3.3 V
  • Locked in mutually exclusive 5 V / 12 V, with manual switch preferred over jumper
  • Added clearer sections for power path, charging behavior, power budget, constraints, risks, and a decisions log
  • Narrowed the remaining uncertainties to a short list so we can finish requirements before schematic work
The remaining questions I still need from you are:
  1. USB-C behavior
    • Do you want:
      • simple USB-C sink-only behavior,
      • BC1.2-style charger detection, or
      • fuller USB-C current negotiation / PD-style behavior?
    • Since your source budget is still 500 mA, my default recommendation would be USB-C sink-only unless you explicitly want more advanced negotiation.
  2. Solar threshold
    • What should count as “usable solar” before the board tries to charge or power from it?
    • If you want, I can choose a conservative threshold rule and document it.
  3. Live switching between 5 V and 12 V
    • During switching while powered, is a brief interruption acceptable?
    • Or must the downstream load see little to no interruption?
  4. Rail quality / sequencing
    • Any hard constraints on:
      • ripple,
      • startup time,
      • brownout tolerance,
      • rail sequencing?
    • If not, I can define conservative defaults in the spec.
  5. Battery connector
    • Should I lock this now to a common JST family, or leave it as an implementation choice until part selection?
If you want, reply in a compact format like:
  • USB-C:
  • Solar threshold:
  • 5 V / 12 V switching:
  • Rail quality / sequencing:
  • Battery connector:
Choose defaults now
Use sink-only USB-C
Lock JST connector
Define rail limits
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Low-Power Embedded Power Management Board e5ec

Low-Power Embedded Power Management Board e5ec thumbnail
Power management board for a low-power embedded system with solar panel, 1S LiPo battery, and USB 2.0 inputs; charges the battery from available external power, powers the system from battery when external sources are absent, prioritizes USB over solar, and generates selectable boosted 12V or 5V output plus a regulated 3.3V rail.

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