Ho letto e consolidato la documentazione R2 e avviato lo schema Rev A. Il progetto ora contiene 53 componenti e 45 reti, inclusi nRF9151, nRF5340, power path, MAX17055 con reti Kelvin, collegamento SPI tra MCU, ES8388/I²S e catena RF 50 Ω.
Lo schema non è ancora pronto per il layout:
L’esecutore iniziale ha riportato 235 segnalazioni ERC.
Mancano ancora verifiche/completamenti per decoupling e pin riservati dei due MCU, shunt Kelvin reale, protezione batteria, consenso USB-C, watchdog/CE, NTC, matrici K1, PTT, UI, debug e test point.
Pinout OLED e alcuni dati meccanici restano non verificati.
Ho rimandato lo schema allo stesso esecutore con istruzioni precise per completare questi punti e ridurre l’ERC, ma non ho potuto recuperarne il nuovo rapporto finale.
Nessun placement, routing o layout PCB è stato avviato: procedere con uno schema ancora non verificato sarebbe rischioso.
Il prossimo passo è recuperare il risultato dell’ultima correzione, eseguire una review indipendente dello schema e, solo dopo ERC accettabile, configurare il PCB JLCPCB a sei strati e iniziare placement e routing.
L’esecuzione si è fermata perché gli ACUs sono terminati.
Non ho potuto recuperare né riconciliare il report dell’executor “Beltpack Schematic Rev A”, quindi non posso confermare che lo schema sia corretto o pronto per il layout. In questa sessione non sono state apportate ulteriori modifiche a schema o PCB.
Restano da completare:
verifica indipendente di componenti, collegamenti, alimentazioni ed ERC;
confronto dello schema con i documenti di specifica allegati;
correzione degli eventuali errori;
definizione del budget di potenza;
solo dopo la validazione dello schema: stackup JLCPCB a 6 strati, profilo scheda, placement, vincoli RF/antenna e routing controllato;
checkpoint di approvazione tra schema verificato e layout.
L’esecuzione si è fermata perché gli ACUs disponibili sono esauriti.
Flux can arrange them into readable blocks and draw the wires. Your connections stay the same.
Takes about 10–60 min, depending on the number of parts
Battery Management Validation Report
Status: Phase 2 validation baseline updated with the locked Rev A cell and holder path. No schematic capture has started.
Scope: single protected removable 18650 Li-ion power system for the DECT NR+ Intercom Beltpack, using JLCPCB standard 6-layer manufacturing assumptions and the Phase 2 preferred battery-management architecture.
Executive Decision
Proceed to schematic planning with this Rev A battery-management architecture:
Table
Function
Rev A choice
Decision
Charger / power-path
TI BQ25895RTWT
Approved for Rev A if safe-default requirements below are implemented.
Fuel gauge
ADI / Maxim MAX17055ETB+T
Approved for Rev A with 10 mΩ Kelvin current-sense resistor.
USB-C current detection
TI TUSB320LAIRWBR
Preferred simple Type-C advertised-current detector for 5 V sink operation.
Protected cell
KeepPower P1835J
Locked Rev A removable cell; separately procured and inserted after PCBA.
Cell holder
MPD BK-18650-PC2
Locked Rev A through-hole removable-cell holder; hand-install, consign, or special-source unless assembly stock is confirmed at BOM lock.
USB-PD sink fallback
HUSB238A or STUSB4500-class
Do not use by default; reserve for later if USB-PD input becomes required.
Simple gauge fallback
MAX17048
Keep as fallback only if MAX17055 schedule/layout risk becomes unacceptable.
The key change from the earlier selection note is that BQ25895 must not be allowed to charge autonomously at its 2.048 A reset/default fast-charge current. Rev A must use a hardware/firmware boot policy that keeps charging disabled or current-limited until the MCU has configured safe charge parameters.
Hard Requirements Before Schematic Capture
No schematic capture may begin until this validation report and the project specification are treated as the battery-management requirements baseline.
BQ25895 charge enable must be deterministic at boot. The charger CE pin shall default to charge-disabled, or an equivalent hardware-safe state, until firmware has configured charge voltage, charge current, input current, watchdog, and safety behavior.
Rev A normal charge current shall default to 1.0 A. A 1.5 A normal option is allowed only after the approved cell is selected and the NTC/thermal layout is validated.
2.0 A charging is engineering-validation only. It shall be disabled in normal firmware and enabled only after cell datasheet, USB-C input capability, enclosure thermal, and simultaneous-system-load tests pass.
USB-C input current shall follow actual advertised capability. A fixed Rd-only USB-C sink is not enough for this design if charging above conservative default USB current is allowed.
Battery temperature sensing is mandatory. BQ25895 TS shall be connected to an NTC thermally coupled to the removable cell or mounted in the cell compartment with validated correlation to cell surface temperature.
Treat the protected 18650 as secondary protection only. The beltpack PCB must still handle reverse insertion, absence, hot insertion/removal, protector-open behavior, and charger faults.
Use JLCPCB standard capabilities only: Shengyi S1000-2M, 6 layers, ENIG, controlled impedance, standard through vias, epoxy-filled/capped vias only where available as a standard JLCPCB option, and no blind/buried/HDI microvias.
Datasheet Facts That Drive the Requirements
BQ25895 Charger / Power Path
Table
Item
Datasheet-backed value / behavior
Design consequence
Input voltage range
3.9 V to 14 V recommended
Compatible with 5 V USB-C input; do not assume PD voltages.
Input current range
Up to 3.25 A input current limit
Enough for 5 V / 3 A Type-C sources if current is advertised and thermals pass.
Fast charge current
Up to 5 A
Capability exceeds safe default for removable 18650; must be configured.
Reset/default fast charge current
2.048 A
Too high as an unvalidated default; require charge-disabled boot or safe configuration before charging.
Default charge voltage
4.208 V
Compatible with 4.2 V Li-ion cells, but final value must match approved cell.
Default input current limit register
500 mA, then may change after source detection
Good safe starting point; firmware still must own the final policy.
ILIM pin
Hardware input-current ceiling; datasheet example 260 Ω for 1.5 A using KILIM max example
Use ILIM as a conservative hardware ceiling, but do not confuse input-current limit with battery fast-charge current.
TS profile
Cold/hot profile; 103AT example gives RT1 = 5.21 kΩ and RT2 = 29.87 kΩ for 0°C to 45°C Li-ion window
Use BQ25895 TS as the primary hardware safety temperature qualification.
BATFET
Supports ship mode, QON wake/reset, over-discharge protection
Useful, but system must validate battery absent/protector-open/hot-swap behavior.
Layout
Tight input capacitor loop, small SW node, inductor adjacent to SW, thermal pad grounded with vias
Requires disciplined power layout; no exotic PCB tech needed.
MAX17055 Fuel Gauge
Table
Item
Datasheet-backed value / behavior
Design consequence
Battery voltage range
2.3 V to 4.9 V operating range; 3.0 V startup typical
Compatible with 1S Li-ion.
Active current
18 µA typical, 30 µA max excluding thermistor current
Acceptable for beltpack standby/runtime goals.
Current measurement range
±51.2 mV
With 10 mΩ, full-scale is ±5.12 A.
Sense resistor range
1 mΩ to 1000 mΩ
10 mΩ is valid and recommended for this capacity class.
Current LSB with 10 mΩ
156.25 µA
Excellent diagnostic resolution for charge/discharge logging.
Recommended sense option for >400 mAh
10 mΩ table row gives ±5.12 A range
Good for 3000–3500 mAh protected 18650.
CSP/CSN routing
Kelvin connect CSP to battery side and CSN to load side; do not share high-current paths; vias on Kelvin traces not recommended
Requires a true Kelvin, quiet routing layout.
Temperature
External thermistor supported; for removable battery, external thermistor divider is recommended
Use a cell-compartment NTC for fuel-gauge temperature if practical, or document reduced accuracy.
TUSB320LAI USB-C Current Detection
Table
Item
Datasheet-backed value / behavior
Design consequence
UFP/sink mode
PORT low; presents Rd on both CC pins and detects DFP advertisement
Suitable for a USB-C sink charger input.
Current reporting
OUT1/OUT2 GPIO or I2C CURRENT_MODE_DETECT
Connect OUT1/OUT2 to MCU; I2C is recommended for diagnostics.
OUT1/OUT2 default unattached
H/H
Treat as no valid high-current source.
OUT1/OUT2 default attached
H/L
Limit input to default USB-safe current.
OUT1/OUT2 medium
L/H = 1.5 A
Allow up to 1.5 A input if charger/thermal policy allows.
OUT1/OUT2 high
L/L = 3.0 A
Allows 5 V / 3 A input, but does not permit 2 A battery charge unless thermal/cell validation passes.
VDD note for 3 A advertisement
Datasheet notes system designer must ensure TUSB320 VDD is at least 3.5 V when DFP advertises 3 A
Check supply implementation; if powered from 3.3 V, validate the exact TUSB320LAI requirement and mode.
Temperature coefficient: low-TCR preferred for fuel-gauge accuracy.
Calculations:
Table
Current
Sense voltage at 10 mΩ
Resistor dissipation
1.0 A
10 mV
10 mW
1.5 A
15 mV
22.5 mW
2.0 A
20 mV
40 mW
3.0 A
30 mV
90 mW
5.12 A MAX17055 full-scale
51.2 mV
262 mW
A 10 mΩ resistor gives enough range for expected beltpack load, charger current, and transient logging without excessive battery-path voltage drop.
Gauge Placement and Routing Requirements
Place MAX17055 near the battery holder/connector and sense resistor.
Put the sense resistor in the battery current path so both charge and discharge current are measured.
Route CSP and CSN as a quiet Kelvin pair directly to the sense resistor pads.
Do not share the Kelvin traces with charger, system, or battery current.
Avoid vias on Kelvin traces where possible.
Keep the gauge and sense lines away from the BQ25895 SW node, inductor, USB VBUS surge paths, OLED switching currents, RF feed, and audio inputs.
Add test points for BAT+, BAT-/PACK reference, CSP, CSN if safe, I2C, ALRT, and gauge temperature input.
Verify sign convention in firmware: charge and discharge polarity must match the MAX17055 configuration.
Fuel-Gauge Temperature
For a removable 18650, the MAX17055 datasheet supports external thermistor measurement and specifically distinguishes removable-pack style measurement. Rev A should do one of the following:
Preferred: provide a second 10 kΩ NTC thermally coupled to the cell compartment for MAX17055 THRM/AIN, separate from the BQ25895 TS safety NTC.
Acceptable for Rev A validation: use BQ25895 TS as the safety NTC and let MAX17055 use internal temperature, but document reduced SOC accuracy under charge/discharge thermal gradients.
Do not directly tie one NTC node to both ICs unless both datasheets and bias timing are verified; competing bias sources can corrupt readings.
Charger / USB-C Validation
Safe BQ25895 Boot Policy
The BQ25895 default fast-charge current is 2.048 A. That is above the desired unvalidated default and can return after reset/watchdog conditions. Therefore Rev A shall implement this boot policy:
CE defaults to charge-disabled using a resistor or equivalent safe hardware state.
MCU boots from SYS when USB is present.
Firmware verifies charger identity over I2C.
Firmware disables or services charger watchdog intentionally.
Firmware sets:
Charge voltage for the approved cell, normally 4.2 V class.
Fast-charge current initially 1.024 A or another exact BQ25895 register value at or below 1.0 A target.
Pre-charge and termination current appropriate for the approved cell.
Firmware reads charger status/fault/ADC and TS state.
Only then may firmware assert CE low to enable charging.
If firmware is absent, crashed, or I2C fails, the safe state is no battery charging, while USB may still power SYS if supported by the charger configuration.
Input-Current Policy
TUSB320LAI shall be authoritative for USB-C Type-C current advertisement. BQ25895 input limits shall not exceed the detected source capability.
Table
TUSB320LAI result
Allowed Rev A input-current policy
Unattached / invalid
Charging disabled or safe low state.
Default attached
500 mA input limit unless USB enumeration/BC1.2 policy justifies more.
1.5 A advertised
Up to 1.5 A input limit.
3.0 A advertised
Up to 3.0 A input limit may be tested, but normal battery charge still limited to 1.0–1.5 A until thermal validation.
Recommended ILIM implementation:
Populate ILIM for a conservative hardware input-current ceiling, initially around 1.5 A using the datasheet example class of resistor value.
Add a resistor option or solder-jumper/test variant if 2.0 A charge validation needs a higher input ceiling.
Keep EN_ILIM enabled unless there is a documented reason to disable it.
Remember: ILIM limits input current, not battery charge current directly.
USB-C / PD Boundary
Rev A remains a 5 V USB-C sink design unless a later requirement adds USB-PD.
Do not assume 9 V, 12 V, 15 V, or 20 V input.
Do not use HUSB238A, STUSB4500, or FUSB302B unless USB-PD is deliberately added.
HUSB238A is technically available and capable, but overqualified for simple 5 V current detection.
FUSB302B requires substantial PD policy-engine firmware and is not the simple path.
STUSB1602A was found as a possible Flux/LCSC part, but TUSB320LAI remains simpler for this 5 V sink-current detection requirement.
Battery Cell and Holder Validation
Locked Rev A mechanical and sourcing path
Table
Item
Locked choice
Verified information
Sourcing / assembly status
Protected cell
KeepPower P1835J protected button-top 18650
3.7 V nominal, 3500 mAh typical / 3350 mAh minimum, 4.2 V maximum charge voltage, protection against overcharge, over-discharge, over-current, and short circuit. Manufacturer maximum envelope is 18.65 mm diameter × 69.25 mm length, ±0.2 mm.
Open single-cell holder, two through-hole PC pins, 21.4 mm nominal height above PCB, polypropylene UL94V-0 body, nickel-plated spring contacts; MPD describes it as intended for protected 18650 cells.
Reserve for the P1835J maximum envelope plus tolerance, installation angle, spring travel, finger/tool access, NTC contact, and enclosure clearance. Do not use a generic 65 mm-cell cavity.
Exact P1835J-to-BK-18650-PC2 fit is a prototype/incoming-inspection gate. Third-party holder listings are inconsistent about the supported protected-cell length, and the holder drawing does not provide an unambiguous maximum accepted cell length. Buy samples from the intended suppliers and verify insertion force, compression, retention, terminal contact, and removal without damaging the cell wrap or protection cap.
The holder contact-current rating is not stated in the available MPD drawing. Treat contact heating and voltage drop at the preliminary 0.65 A system peak, at protected-cell fault transients, and during charge/discharge tests as a validation gate. Do not infer a current rating from contact material.
Preserve removable-cell service: provide end access for finger or insulated pull-tab removal, prevent tools from shorting the cell ends, and ensure the enclosure—not only the solder joints—reacts insertion/removal force.
Mark polarity clearly on PCB, holder area, and enclosure. Add electrical reverse-polarity protection because an open holder alone is not sufficient keying.
The P1835J remains the only approved Rev A cell. Flat-top or unprotected substitutes are not approved.
Rejected LCSC/JLC holder option
MYOUNG BH-18650-B1BA002, LCSC/JLCPCB C2988620, is rejected for the P1835J baseline. It is cataloged as an SMT 18650 holder, but the selected protected button-top cell compatibility and 69.25 mm maximum length are not demonstrated; project research identified it as a flat-top path. Catalog stock does not overcome the mechanical-compatibility gap.
Other LCSC clips or wire-lead holders are not substitutions unless their drawings explicitly accommodate the locked cell envelope, polarity, retention, current, and removal requirements.
Charge-current implication of the locked cell
Keep the approved 1.0 A default. The manufacturer product page used for the dimensional lock does not publish an authoritative charge-current table, so 1.5 A remains validation-only pending a lot-specific KeepPower specification or written manufacturer confirmation.
1.5 A may become the normal option only after supplier documentation, NTC correlation, closed-enclosure thermal testing, and cycle/temperature review.
2.0 A remains engineering-only and is not presently approved for P1835J normal charging.
NTC / JEITA / Thermal Requirements
BQ25895 TS is the primary hardware battery-temperature safety input.
Recommended starting point:
NTC type: 10 kΩ 103AT-class NTC or exact equivalent used by the BQ25895 datasheet example.
Charge window: 0°C to 45°C minimum, matching the datasheet example network.
Example divider values from BQ25895 datasheet for 103AT and 0°C to 45°C: RT1 = 5.21 kΩ, RT2 = 29.87 kΩ.
Physical placement: NTC shall touch or closely track the cylindrical cell surface, ideally with a spring/contact feature or thermally coupled holder feature.
Holder integration: use a spring finger, compliant pad, or retained sensor feature that keeps the BQ25895 safety NTC pressed against the P1835J sleeve near the middle third of the can across repeated removal cycles. Adhesive alone shall not be the only retention method.
Verify that the NTC cannot be displaced, pinched, or shorted by cell insertion and that the sensor does not damage the wrapper.
Validate NTC reading versus actual cell surface temperature.
Validate USB-C default, 1.5 A, and 3.0 A source detection.
Validate input current limit never exceeds advertised source capability.
Validate simultaneous charging and worst-case radio/audio/OLED load.
Validate battery absent, hot insertion, removal, reverse-insertion attempt, protector-open, and deeply discharged cell cases.
Complete incoming inspection of the actual P1835J and BK-18650-PC2 lots: maximum measured diameter/length, insertion force, removal force, spring compression, contact resistance, polarity, NTC contact pressure, wrap abrasion, and ten-cycle retention check.
Measure holder/contact temperature rise and voltage drop at the final measured system peak and fault-test current; establish an approved current rating from supplier confirmation or prototype evidence.
Before 2.0 A charging is allowed:
Use only a cell whose datasheet permits 2.0 A or higher charging.
Use a USB-C source advertising enough current with margin.
Run closed-enclosure high-ambient thermal testing.
Run simultaneous system-load charging tests.
Confirm charger thermal regulation is not the normal operating mode.
Confirm cell surface remains within the approved cell charge-temperature limit.
Enable only through engineering firmware/configuration until product validation passes.
Final Recommendation
Use KeepPower P1835J + MPD BK-18650-PC2 + MAX17055ETB+T + BQ25895RTWT + TUSB320LAIRWBR for Rev A, but only with the safe-default and validation requirements above. The cell is separately procured; the holder is PCB-compatible but not confirmed as assembly-stocked. The schematic must be designed so an unconfigured charger cannot silently charge the removable cell at 2.048 A.
Schematic capture may proceed after user approval of these requirements.