LC709209FXE-01TBG - 1-Cell Li-Ion Fuel Gauge | onsemi
MPN: LC709209FXE-01TBG β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.57 | $1.57 |
| 10 | $1.57 | $15.70 |
| 100 | $1.57 | $157.00 |
| 500 | $1.57 | $785.00 |
| 1,000 | $1.57 | $1,570.00 |
LC709209FXE-01TBG Overview
A battery fuel gauge is a power-management IC that estimates the state of charge (SOC) of a rechargeable cell and reports it to a host microcontroller. Within the power-management hierarchy, the fuel gauge sits alongside chargers and protectors in the battery management IC category, converting cell voltage and current behavior into a usable percentage readout. Accurate gauging is essential in portable systems because cell voltage alone is a poor predictor of remaining capacity, especially across different battery chemistries and load profiles.
Key features of the LC709209FXE include its dedicated 1-cell Li-ion/Li-polymer support, I2C digital interface for host communication, ultra-compact 12-WLCSP (1.48 x 1.91 mm) footprint suited to space-constrained wearables and IoT devices, and Pb-free and halogen-free construction per the onsemi data sheet. The device is supplied in tape and reel packaging (refer to onsemi BRD8011/D for tape and reel specifications).
From a technical perspective, the Smart LiB Gauge architecture performs SOC estimation based on cell voltage monitoring with profile-based algorithms, requiring minimal external components. Because it gauges by voltage, integration into a design is straightforward: connect the cell voltage sense line, the I2C bus, and the supply rails. Host software reads SOC values through the I2C register map, allowing firmware-level power management decisions such as low-battery shutdown or capacity reporting to an operating system.
Typical applications include true wireless stereo (TWS) earbuds, smartwatches and fitness bands, small IoT sensor nodes, and other single-cell portable products where board area is at a premium and battery life reporting is a user-facing feature.
When designing with this part, verify the I2C address and pull-up resistor sizing against the host bus loading, and confirm the battery profile matches the cell chemistry in use, since gauging accuracy depends on correct cell characterization.
This page synthesizes distributor pricing, availability, cross-reference findings, and practical design notes not consolidated in the manufacturer data sheet, with pricing verified as of 2026-09-13.
Drop-in alternatives for LC709209FXE-01TBG β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
LC709209FXN-01TBG
β Drop-Inπ Reference alternative (not in catalog)
LC709209FXE-01TBG Specifications
| Function | Battery Fuel Gauge IC |
| Battery Chemistry | Lithium Ion / Lithium Polymer |
| Battery Cell Count | 1 cell |
| Interface | I2C |
| Package | 12-WLCSP (1.48 x 1.91 mm) |
| Mounting Type | Surface Mount |
| Category | Battery Management |
| Family | Smart LiB Gauge (LC709209F) |
| Pb-Free | Yes |
| Halogen-Free | Yes |
| Packaging | Tape & Reel |
| Tape & Reel Reference | onsemi BRD8011/D |
LC709209FXE-01TBG 12-wlcsp (1.48 x 1.91 mm) Pin Configuration Guide
Pin configuration for LC709209FXE-01TBG (12-wlcsp (1.48 x 1.91 mm) package). Pin numbering, functions, and connection diagrams are defined in the manufacturer datasheet. Refer to it for the exact footprint and soldering guidelines.
No detailed pinout data available for LC709209FXE-01TBG.
Refer to the datasheet for full pin configuration.
Typical Applications
LC709209FXE-01TBG is suitable for 6 applications: True Wireless Stereo (TWS) Earbuds, Smartwatches and Fitness Bands, IoT Sensor Nodes, Portable Medical Monitoring Devices, Bluetooth Beacons and Asset Trackers, Small Rechargeable Consumer Electronics.
True Wireless Stereo (TWS) Earbuds
TWS earbuds are the canonical use case for the LC709209FXE-01TBG: the 12-WLCSP package at just 1.48 x 1.91 mm fits on the cramped battery-protection PCB inside an earbud shell, where every square millimeter counts. Its voltage-based single-cell Li-ion gauging requires no sense resistor and minimal external components, keeping the BOM lean. The I2C interface connects directly to the Bluetooth audio SoC, which reports battery percentage to the smartphone. Because earbud loads are light and fairly steady, voltage-based SOC estimation maintains practical accuracy without coulomb counting. Place the IC close to the battery terminal with short sense traces, and poll the SOC register periodically rather than continuously to conserve system power.
Recommended
Smartwatches and Fitness Bands
In smartwatches and fitness bands, the LC709209FXE-01TBG provides state-of-charge data for the user-facing battery icon and for firmware power-management decisions. The 1.48 x 1.91 mm WLCSP footprint suits the dense, stacked boards typical of wearables, and the I2C bus is already present for the sensor hub and display controller, so integration adds only a slave address. Wearable loads are pulsed but moderate; the voltage-based gauging algorithm of the Smart LiB Gauge family handles this acceptably at lower cost than a coulomb counter. Designers should pair the gauge with the correct battery profile for their cell and schedule SOC reads after load transients settle, improving percentage-report stability across charge and discharge cycles.
Recommended
IoT Sensor Nodes
Battery-powered IoT sensor nodes benefit from the LC709209FXE-01TBG's ability to report remaining capacity to the network, enabling predictive battery replacement and fleet battery analytics. The device's minimal external component count and tiny WLCSP footprint suit low-cost, coin-cell or small Li-polymer powered nodes that sleep most of the time. The MCU reads SOC over I2C once per wake cycle, adding negligible energy overhead to the duty cycle. Because the gauge monitors cell voltage, it also gives firmware an implicit low-voltage warning for graceful data flush before brownout. For nodes with very high pulsed transmit currents, verify gauging accuracy under your load profile, or buffer the radio rail to reduce voltage sag seen by the gauge.
Recommended
Portable Medical Monitoring Devices
Compact medical wearables and portable monitors need trustworthy battery reporting for patient safety and regulatory documentation. The LC709209FXE-01TBG supplies SOC over I2C to the host MCU, which can log battery state alongside vitals data and trigger conservative low-battery behavior. Its Pb-free and halogen-free construction per the onsemi data sheet supports common environmental compliance requirements, and the 12-WLCSP package suits patch-style and handheld form factors. Note that voltage-based gauging accuracy depends on correct cell characterization for the specific Li-ion or Li-polymer pack used; validate SOC readings across the medical device's full temperature and load range during design verification, and document the gauging behavior in your risk management file.
Recommended
Bluetooth Beacons and Asset Trackers
Asset trackers and Bluetooth beacons run for months on a small single-cell Li-polymer battery, making remaining-capacity visibility valuable for maintenance scheduling. The LC709209FXE-01TBG reports SOC via I2C on each advertising or GPS-fix wake cycle at near-zero average cost, and its 1.48 x 1.91 mm WLCSP fits the ultra-thin PCBs used in card-style trackers. Because beacon loads are dominated by short radio bursts, place the gauge sense connection at the battery terminal rather than after high-current switching paths to minimize sag-induced SOC misreads. Firmware can combine SOC trends with radio-current estimates to adapt advertising intervals dynamically, extending usable battery life by weeks before replacement or recharge.
Recommended
Small Rechargeable Consumer Electronics
Beyond wearables, the LC709209FXE-01TBG fits any compact single-cell product that reports battery level: electric toothbrushes, small remote controls, mini fans, LED cues, and rechargeable accessories. Its value proposition is consistent across these products: an I2C digital SOC output, no sense resistor, minimal board area in the 12-ball WLCSP, and Pb-free/halogen-free construction. Consumer products with simple button-cell-style Li-polymer packs and modest loads achieve acceptable gauging accuracy with the Smart LiB Gauge voltage-based method. Designers should verify the I2C address does not collide with other bus devices, add standard bus pull-ups, and expose the SOC register to the product's status LED or app so end users see an accurate, stable battery indicator throughout the discharge curve.
Recommended
Recommended Products Summary
Engineering reference data for LC709209FXE-01TBG β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | LC709209FXN-01TBG | MAX17048G+T |
|---|---|---|---|
| Package | 12-WLCSP (1.48 x 1.91 mm) | 12-WLCSP (1.48 x 1.91 mm) - same | Different package (not drop-in) |
| Brand | onsemi | onsemi | Analog Devices |
| Function | 1-cell Li-ion/Li-polymer fuel gauge | 1-cell Li-ion/Li-polymer fuel gauge | 1-cell Li-ion fuel gauge |
| Interface | I2C | I2C | I2C |
| Battery Cell Count | 1 cell | 1 cell | 1 cell |
| Drop-in Footprint Compatibility | Reference | Yes - identical ball map | No - requires PCB rework |
Key Differentiators
- Identical-die family variant for supply flexibility (vs LC709209FXN-01TBG)
- Ultra-compact WLCSP footprint (vs MAX17048G+T)
- Sense-resistor-free voltage gauging (vs Coulomb-counter gauges)
Design Notes
WLCSP packages route traces directly under the die, so the PCB land pattern must follow the onsemi data sheet ball map exactly, including any recommended via-in-pad or escape routing. Keep the cell voltage sense trace short and routed directly from the battery positive terminal to minimize series resistance that could skew voltage-based SOC readings. For assembly, confirm your stencil aperture design follows onsemi WLCSP application recommendations, and handle per the moisture sensitivity instructions on the product page to avoid delamination during reflow.
Because the LC709209FXE gauges by cell voltage, connect its sense input as close to the battery terminal as possible and avoid sharing the trace with high-current load paths. Pulsed loads such as radio transmitters cause transient voltage sag that the gauge can interpret as a sudden SOC drop. If your load profile is heavily pulsed, add local bulk capacitance at the load or average SOC readings in firmware over several samples after load transients settle to stabilize reported battery percentage.
The I2C bus is the only host interface, so its reliability defines gauge usability. Size pull-up resistors for your bus capacitance and target speed (typical portable designs use 4.7k to 10k ohm at standard 100/400 kHz speeds), keep the bus short, and verify the LC709209FXE slave address does not conflict with other devices sharing the bus. During firmware development, validate SOC register reads across the full battery discharge curve and at low temperature, where battery internal resistance rises and voltage-based gauging accuracy is most affected.
Compliance Information
Per the onsemi LC709209F data sheet, the LC709209FXE-01TBG ordering code specifies Pb-Free and Halogen-Free construction. REACH and conflict-minerals declarations were not stated in the provided data.
