AnasSarkiz/ble-pedometer

POWER_BUDGET.md

# Power budget

Typical-value sizing model for the BQ25186 + TPS7A02 revision, not measured data. Cold, aging, RF retries, regulator dropout and component leakage need qualification.

| Load | Assumption | Average |
|---|---|---:|
| CC2340R5 standby | RAM/RTC retained | 0.71 µA |
| BMA400 | normal mode, OSR3 | 14.50 µA |
| BQ27427 | sleep approximation | 9.00 µA |
| Charger, regulator and CE bias | 4 µA charger + 0.025 µA LDO + approximately 0.65 µA CE bias, rounded up | 5.00 µA |
| CPU housekeeping | 3 mA, 40 ms/min | 2.00 µA |
| Other leakage margin | pull-ups, switches, capacitors | 3.00 µA |
| BLE advertising | 20 µC/event every 2 seconds | 10.00 µA |
| OLED | 20 mA, 3 seconds, 10 sessions/day | 6.94 µA |
| **Electronics total** | | **51.15 µA** |

The power-stage assumptions use TI's [BQ25186](https://www.ti.com/product/BQ25186) battery-only operation and [TPS7A02](https://www.ti.com/product/TPS7A02) typical quiescent current. Ship mode is not normal pedometer sleep: it disconnects the system.

Budget = electronics × 1.15 + capacity × 3% / 720 hours. Use 80% of nameplate capacity. A 150 mAh cell at the example profile gives about 65.08 µA budgeted battery current and **77 days**, before measured corrections.

## Sensitivity

Each column includes its own capacity-dependent self-discharge, not a shared fixed current.

| Advertising interval | OLED sessions/day | 100 mAh | 150 mAh | 200 mAh |
|---|---:|---:|---:|---:|
| 1 second | 0 | 50 days | 73 days | 94 days |
| 1 second | 10 | 45 days | 65 days | 85 days |
| 5 seconds | 0 | 69 days | 100 days | 128 days |
| 5 seconds | 10 | 59 days | 86 days | 111 days |

A 3-second, 20 mA display session costs 0.0167 mAh. Higher display current, GPIO contention or failure to isolate the unpowered display can materially shorten life.

## Measurement acceptance

Measure battery current with calibrated equipment. Provisional targets: display-off current below 40 µA between radio events, no unexplained milliamp plateaus, and 24-hour coulomb consumption within ±25% of the model. Verify charge current and temperature inhibition separately.

TPS7A02's nominal 3.3 V output cannot be maintained below its required input headroom. Qualify radio/display transients and disable the OLED below a measured safe threshold. The 80% usable-capacity assumption does not establish this threshold. Publish no battery-life claim until first-article measurements replace these assumptions.