Key locked decisions: MAX17055ETB+T + BQ25895RTWT + TUSB320LAIRWBR, 1.0 A default charge, 1.5 A only after validation, 2.0 A engineering-only, BQ25895 charge disabled until firmware configures safe settings, and mandatory cell-temperature/USB-C current validation.
Suggested next steps:
Approve these battery-management requirements as the schematic baseline.
Select the exact protected 18650 cell and holder.
Continue Phase 2 with radio/MCU/audio architecture comparison before schematic capture.
Status: Phase 2 selection note for Rev A schematic planning.
Scope: compare the requested fuel gauges and charger / power-path ICs for a single protected removable 18650 Li-ion beltpack powered and charged from USB-C 5 V, assembled by JLCPCB using standard 6-layer controlled-impedance capabilities.
Executive Decision
Recommended Rev A battery-management pair:
Fuel gauge: MAX17055ETB+T.
Charger / power-path IC: BQ25895RTWT or same RTW package ordering variant available for assembly.
The MAX17055 gives more useful runtime diagnostics than the MAX17048 while avoiding the heavier TI Impedance Track configuration burden of the BQ27441/BQ27542 family. The BQ25895 is the best fit among the charger candidates because it is single-cell focused, mature, available in the Flux/JLCPCB/LCSC ecosystem, supports switch-mode charging, has NVDC-style power-path behavior, and avoids the unnecessary 1-4 cell / PD / MPPT complexity of BQ25792 and BQ25672.
Important constraint: USB-C 5 V / 3 A input is a source capability, not a default charge current. Rev A should start at 1.0-1.5 A charge current and allow 2.0 A only after cell datasheet, enclosure thermal, and USB-C current-advertisement validation.
PCB / JLCPCB Manufacturing Assumptions
Use JLCPCB standard capabilities only:
Manufacturer: JLCPCB.
Material: Shengyi S1000-2M.
Layer count: 6.
Nominal board thickness: 1.6 mm unless mechanical design changes it.
Finish: ENIG.
Via technology: through vias; epoxy-filled and capped vias are allowed if ordered as a JLCPCB standard capability.
Controlled impedance: yes, using a standard JLCPCB 6-layer stackup.
Do not use exotic PCB technologies: no blind vias, no buried vias, no HDI microvias, no unusual materials, no nonstandard copper weights unless specifically justified.
The screenshot shows standard JLCPCB 6-layer 1.6 mm stackup options such as JLC06161H-3313, JLC06161H-7628, JLC06161H-1080, JLC06161H-2116A/B, JLC06161H-3313C/D/E, JLC06161H-1080A/B, and JLC06161H-7628A/B. Final stackup should be chosen during RF/USB/layout setup using the JLCPCB impedance calculator so the 50 ohm DECT RF feed and any USB 2.0 differential pair geometry match the actual copper/core/prepreg option.
Preliminary Power Sizing Check
The Phase 1 power budget estimated normal mixed-use system power around 0.65-0.95 W, continuous coordinator/relay around 1.0-1.5 W, and worst continuous TX/RX around 1.5-2.0 W.
For USB-C 5 V input with a switch-mode charger:
Table
Case
Battery charge power
Approx input current for charging at 90% efficiency
Add system load from USB
Planning interpretation
1.0 A at 4.2 V
4.2 W
0.93 A
~0.2-0.45 A
Easy on 5 V / 1.5 A or 3 A source if thermals pass.
1.5 A at 4.2 V
6.3 W
1.40 A
~0.2-0.45 A
Good Rev A target with Type-C current awareness and thermal testing.
2.0 A at 4.2 V
8.4 W
1.87 A
~0.2-0.45 A
Possible from 5 V / 3 A source, but enclosure and cell temperature dominate.
3.0 A at 4.2 V
12.6 W
2.80 A
~0.2-0.45 A
Not appropriate as a default; exceeds or crowds 5 V / 3 A once system load and losses are included.
Rev A design target: configure the charger and firmware so the default charge current is conservative, then expose test points and telemetry to validate higher current safely.
USB-C implementation note: a USB-C receptacle with only Rd pull-downs cannot assume 3 A from every source. Either add a simple Type-C current-detection controller or set the input current limit conservatively until firmware can identify the source capability.
Fuel Gauge Comparison
Table
Candidate
Type
Strengths
Risks / drawbacks
JLCPCB / Flux status
Rev A decision
MAX17048
ADI/Maxim 1S ModelGauge, voltage/model-based, no sense resistor
Very low hardware complexity, low current, I2C, tiny TDFN option, no current shunt, easy bring-up
Less robust under pulsed RF/audio loads, aging, temperature variation, and removable-cell uncertainty; reports less diagnostic current/capacity detail
Flux library match found: MAX17048G+T10, LCSC Extended, TDFN option
Keep as low-risk fallback only
MAX17055
ADI/Maxim 1S ModelGauge m5 EZ with current sensing
Better SOC robustness, voltage/current/SOC/capacity/time-to-empty/age reporting, no heavy learning workflow, I2C, TDFN package
Needs sense resistor, Kelvin routing, and more careful layout than MAX17048
Flux library and LCSC matches found: MAX17055ETB+T, TDFN-10, LCSC Extended
Recommended
BQ27441
TI system-side Impedance Track gauge for 1S Li-ion
Mature TI gauge, system-side use, SOC/SOH/capacity, I2C, JLC/LCSC availability
Requires sense resistor and TI gauge configuration/chemistry workflow; more firmware/bring-up effort than MAX17055
Flux library match found: BQ27441DRZT/DRZR variants, LCSC Extended
Viable alternate if TI gauge ecosystem is preferred
BQ27542
TI pack-side Impedance Track gauge for 1S smart packs
Powerful pack-side feature set, high capacity range, authentication/logging features
More appropriate inside a smart battery pack than on the beltpack PCB; highest configuration burden; unnecessary for Rev A
Flux library matches found, LCSC Extended, but fewer options
Avoid for Rev A
Fuel Gauge Recommendation
Use MAX17055ETB+T for Rev A.
Design notes:
Place the gauge near the battery connector and current-sense resistor.
Use Kelvin connections for CSP/CSN sense routing.
Use a low-value precision sense resistor in the battery current path; 10 mOhm is a reasonable first planning value subject to datasheet/reference-circuit confirmation.
Keep gauge sense traces away from charger SW node, inductor, and high di/dt loops.
Add test points for BAT+, BAT-, gauge I2C, ALERT, and the sense resistor Kelvin nodes.
Firmware should log voltage, current, SOC, remaining capacity, and temperature during charge/discharge/radio tests.
Use MAX17048 only if schedule risk matters more than SOC robustness and the product can tolerate an approximate battery indicator.
Charger / Power-Path Comparison
Table
Candidate
Topology / role
Strengths
Risks / drawbacks
JLCPCB / Flux status
Rev A decision
BQ25792
TI 1-4S 5 A buck-boost charger, NVDC, USB-PD OTG capable
Very capable, wide 3.6-24 V input, 5 A charge, integrated ADC, USB-PD/PPS-friendly OTG, high integration
Overkill for 1S 5 V charging; more pins/registers/layout complexity; unnecessary unless >5 V input, 2S-4S pack, or advanced OTG is required
Flux library and LCSC matches found: BQ25792RQMR, QFN-29, LCSC Extended
Avoid for Rev A unless PD/multicell requirement appears
BQ25895
TI 1S 5 A switch-mode charger with power path and OTG boost
Single-cell focused, mature, I2C, input current limit, NVDC-style power path, OTG boost, 4 mm QFN, good JLC availability
Still a switching charger requiring disciplined layout; USB-C CC/current detection is external
Flux library and LCSC match found: BQ25895RTWT, WQFN-24, LCSC Extended
Recommended
BQ25672
TI 1-4S 3 A buck charger with dual input, MPPT, ADC
Modern, integrated ADC, dual-input and MPPT useful for solar/multisource designs
Not aligned with simple 5 V USB-C 1S design; multi-cell/MPPT complexity; buck topology/input requirements are less attractive for 5 V-only charging
MPS 1S 4.5 A switch-mode charger with NVDC, OTG, ADC, I2C
Functionally attractive single-cell charger, compact QFN-26, good feature fit on paper
Not found as a usable Flux library part; weaker JLCPCB/Flux ecosystem confidence for immediate schematic capture; would require part creation/import
Web-confirmed part exists, but Flux library search found no usable match; missing-part request filed
Avoid for Rev A unless user specifically wants MPS path and accepts library creation
Charger Recommendation
Use BQ25895RTWT for Rev A.
Design notes:
Use switch-mode layout exactly following the TI reference layout: tight input capacitor loop, compact SW node, inductor adjacent to SW, short BAT/SYS current path, and solid thermal-pad copper.
Keep SW/inductor copper away from MAX17055 sense traces, audio codec input, microphone bias, and RF feed.
Add NTC / JEITA battery temperature monitoring; do not rely only on protected-cell internal protection.
Expose charge status, fault, I2C, SYS, BAT, VBUS, PMID, and NTC test points.
Add firmware control of input-current limit and charge-current limit.
Add USB-C CC handling outside the charger. For Rev A, a simple Type-C current detector is preferred over a full USB-PD controller unless later power requirements justify PD.
Default charge current should be 1.0-1.5 A. Allow a 2.0 A firmware/test option only after thermal validation.
Why Not USB-PD / Buck-Boost by Default
The beltpack uses one protected 18650 cell. A 5 V / 3 A USB-C source can provide up to 15 W before cable/source losses, which is already enough for conservative 1.0-2.0 A single-cell charging plus system operation if current advertisement is respected.
A PD buck-boost charger such as BQ25792 becomes justified only if one of these requirements is added:
9 V / 12 V / 15 V / 20 V USB-PD input is required.
Charging above the practical 5 V / 3 A budget is required.
The battery pack changes to 2S-4S.
The device must source high-power programmable USB-C OTG.
Dual-source or adapter-management requirements exceed BQ25895 capability.
None of those are currently required for Rev A.
Recommended Rev A Power Architecture
Diagram
Schematic Capture Implications
Add these parts and support circuits in the power block during schematic capture:
BQ25895RTWT charger/power path.
MAX17055ETB+T fuel gauge.
USB-C receptacle with CC handling and ESD.
Input protection / fuse strategy sized after the full power budget.
Charger inductor, input/output/BAT capacitors, bootstrap/support parts, NTC network, and status/test pins per TI reference design.
MAX17055 sense resistor, decoupling, I2C pull-ups if not shared, ALERT net, and test points.
Battery connector/holder strategy with reverse-insertion and serviceability review.
Current-measurement jumpers or 0 ohm links for BAT and SYS if they do not compromise high-current paths.
Before freezing charger passives, complete the detailed rail-by-rail power budget and reflect all loads through SYS/VBUS at worst-case input and charge conditions.
Open Validation Items
Confirm selected 18650 cell maximum recommended charge current and temperature limits.
Decide whether Rev A uses simple CC Rd resistors plus conservative input current, or a Type-C current-detection controller.
Run charger thermal simulation/bench test at 1.0 A, 1.5 A, and 2.0 A in enclosure-like conditions.
Validate MAX17055 SOC accuracy under DECT NR+ TX/RX bursts, OLED activity, audio amplifier load, and removable-cell swaps.
Confirm JLCPCB stock/assembly class at time of BOM lock; all selected active ICs are Extended-class candidates today, so availability must be rechecked before ordering.
Select final JLCPCB 6-layer stackup and controlled-impedance geometry before RF/USB layout.
Sources / Evidence
ADI MAX17048 product/datasheet: 1-cell ModelGauge fuel gauge, I2C, 3 uA hibernate, no sense resistor, TDFN/WLP packages.
ADI MAX17055 product/datasheet: 1-cell ModelGauge m5 EZ fuel gauge, I2C, current/voltage/SOC/capacity/time reporting, TDFN/WLP packages.
TI BQ27441-G1 datasheet/product page: 1S system-side Impedance Track fuel gauge, I2C, VSON-12, 200-8000 mAh class.
TI BQ25792 datasheet/product references: 1-4S 5 A buck-boost charger, I2C, dual input, USB-PD OTG, QFN-29.
TI BQ25895 datasheet/product references: 1S 5 A switch-mode charger with power path, I2C, boost/OTG, WQFN-24.
TI BQ25672 datasheet/product references: 1-4S 3 A buck charger, dual input, MPPT, ADC, QFN-29.
MPS MP2731 product/datasheet references: 1S 4.5 A switching charger with I2C, NVDC power path, OTG, ADC, QFN-26; not currently found as a usable Flux library component.
Flux library searches confirmed usable matches for MAX17048, MAX17055, BQ27441, BQ27542, BQ25792, BQ25895, and BQ25672. MP2731 was not found in the Flux library and a missing-part request was filed.