LC709209FXE-01TBG - 1-Cell Li-Ion Fuel Gauge | onsemi
MPN: LC709209FXE-01TBG β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.57 | $1.57 |
| 10 | $1.44 | $14.40 |
| 100 | $1.31 | $131.00 |
| 500 | $1.2 | $600.00 |
| 1,000 | $1.1 | $1,100.00 |
LC709209FXE-01TBG Overview
A battery fuel gauge is a power-management IC that estimates the remaining capacity of a rechargeable battery. Within the power management IC hierarchy, it sits alongside battery chargers and protectors, but its role is measurement rather than energy transfer: it translates cell voltage, and in this family internal modeling, into a percentage-of-full-charge value a host microcontroller can read. Gauges are essential in any product where accurate runtime indication or low-battery warnings matter.
Key features of the LC709209F family include ultra-low power consumption that minimizes drain on the host cell, an I2C-compatible two-wire interface for state-of-charge and status readout, Pb-free and halogen-free construction, and an extremely small 12-WLCSP footprint suited to wearables, true-wireless earbuds, and other handheld electronics. According to the onsemi LC709209F data sheet, the device is specified as a Smart LiB Gauge for 1-cell applications.
Technically, the gauge monitors the single-cell pack voltage through an internal ADC path and applies the manufacturer's gauge algorithm to derive state of charge; configuration and status registers are accessible via the I2C bus, allowing the host to read SOC, voltage, and alarm flags and to adjust operating parameters. The WLCSP ball layout keeps external component count minimal, supporting very dense PCB layouts.
Typical applications include smartphone and wearable battery monitoring, true-wireless stereo earbud charging cases, portable medical sensors, and IoT asset trackers where a 1-cell Li-ion/Li-polymer pack must be monitored with minimal board area and quiescent drain.
Design consideration: WLCSP devices require careful PCB land-pattern design per the manufacturer's packaging specification, and the I2C bus should include appropriate pull-up resistors sized for the chosen bus speed.
This page adds distributor pricing, cross-reference data, and application guidance not consolidated in the manufacturer data sheet.
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 |
| Battery Chemistry | Lithium Ion / Lithium Polymer |
| Cell Configuration | 1 Cell |
| Interface | I2C |
| Package | 12-WLCSP (1.48 x 1.91 mm) |
| Mounting Type | Surface Mount |
| Pb-Free | Yes |
| Halogen-Free | Yes |
| Packaging | Tape & Reel (per onsemi BRD8011/D brochure) |
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 Earbuds and Charging Cases, Smart Wearables and Fitness Bands, Portable IoT Asset Trackers, Portable Medical and Health Monitors, Smartphone and Tablet Battery Management, Handheld Test and Measurement Instruments.
True-Wireless Earbuds and Charging Cases
TWS earbud batteries are tiny Li-polymer cells where every square millimeter of PCB counts, and the LC709209FXE-01TBG fits this constraint with a 12-ball WLCSP of only 1.48 x 1.91 mm, smaller than most 0402 passive arrays. Its I2C interface connects directly to the earbud SoC, letting firmware read state of charge and alarm flags without an external ADC channel. The gauge's low-power architecture minimizes parasitic drain on the small cell, which directly extends playtime between charges. Placed across the cell terminals with the sense routing kept short, it reports SOC that remains meaningful under the pulsed load profile of Bluetooth LE audio transmission, where instantaneous voltage sag would otherwise mislead a voltage-only measurement.
Recommended
Smart Wearables and Fitness Bands
Fitness bands and smartwatch-class wearables use compact single-cell Li-polymer packs and require runtime accuracy as a core user feature. The LC709209FXE-01TBG provides dedicated state-of-charge reporting over I2C with the gauge computation done on-chip, freeing the wearable MCU from managing ADC sampling and charge-model math. Its Pb-free, halogen-free construction supports the environmental declarations these consumer products require, and the 1.48 x 1.91 mm footprint fits beneath a shield or beside the wireless module in dense stacked PCBs. Because wearable discharge profiles are bursty, a dedicated gauge yields steadier SOC readings than voltage thresholds alone, and the device's low quiescent drain avoids a measurable penalty on the small cells typical of this category.
Recommended
Portable IoT Asset Trackers
Battery-powered asset trackers spend most of their life in sleep, waking briefly to obtain a GNSS fix and transmit. Battery runtime prediction is a headline spec for these products, and the LC709209FXE-01TBG supplies a host-readable state-of-charge value over I2C that firmware can report upstream alongside GPS coordinates. Its small 12-WLCSP footprint suits the minimal tracker PCB, and the gauge's low-power operation keeps self-discharge contribution negligible during long sleep intervals. Placed directly across the 1-cell Li-SOCl2-unfriendly Li-ion or Li-polymer pack with an I2C pull-up network, the gauge allows the cloud backend to schedule maintenance swaps based on true remaining capacity rather than coarse voltage estimates that collapse abruptly near end of discharge.
Recommended
Portable Medical and Health Monitors
Battery-powered medical monitors, from pulse oximeters to glucose meters, must not fail silently from an exhausted cell, so an accurate fuel gauge is a functional-safety-adjacent necessity. The LC709209FXE-01TBG monitors a 1-cell Li-ion or Li-polymer pack and reports SOC plus alarm status over I2C, letting the device warn the user well before end of charge. The 1.48 x 1.91 mm WLCSP integrates into compact handheld enclosures, and Pb-free halogen-free construction aids regulatory documentation. Its low power draw is important for devices that remain on standby between spot measurements, and the digital interface keeps the analog front end free for the physiological sensor rather than battery diagnostics.
Recommended
Smartphone and Tablet Battery Management
Even where a main gauge exists, secondary gauges are used in smartphone accessories, styluses, and battery cases. The LC709209FXE-01TBG provides a compact 1-cell gauge with I2C readout that integrates into these accessory form factors where the main phone gauge is unavailable. The 12-WLCSP at 1.48 x 1.91 mm fits the thin flex and rigid-flex boards common in accessories, and Pb-free halogen-free construction aligns with the environmental requirements of tier-one consumer suppliers. Because the gauge is readable via a standard I2C bus, accessory firmware can report charge state to the host phone over the existing connection, delivering a polished user experience at minimal board cost.
Recommended
Handheld Test and Measurement Instruments
Handheld multimeters, environmental meters, and portable diagnostic tools increasingly run from single-cell Li-ion packs instead of disposable batteries. The LC709209FXE-01TBG gives these instruments a precise percentage-of-charge indication over I2C, which is displayed directly to the technician. Its 12-WLCSP footprint of 1.48 x 1.91 mm occupies negligible space on the main PCB, and the low-power gauge operation suits instruments that idle between measurements. Because gauge computation is internal, firmware effort is limited to register reads and display formatting. Placed across the pack with short sense traces, it remains accurate under the pulsed measurement loads these instruments generate, where a raw voltage divider would read pessimistically during current spikes.
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+T10 |
|---|---|---|---|
| Brand | onsemi | onsemi | Analog Devices |
| Package | 12-WLCSP (1.48 x 1.91 mm) | 12-WLCSP - same footprint | Different package (TDFN) - not footprint compatible |
| Battery Chemistry | Li-Ion / Li-Polymer | Li-Ion / Li-Polymer | Li-Ion / Li-Polymer |
| Cell Count | 1 Cell | 1 Cell | 1 Cell |
| Interface | I2C | I2C | I2C |
Key Differentiators
- Footprint-compatible dual sourcing within the onsemi family (vs LC709209FXN-01TBG)
- Extremely small footprint (vs MAX17048G+T10)
- Integrated gauge computation with standard I2C (vs Discrete ADC voltage sensing)
Design Notes
The LC709209FXE-01TBG is a 12-ball WLCSP, so the land pattern must be taken directly from the onsemi LC709209F data sheet rather than adapted from QFN footprints. Use non-solder-mask-defined pads where the data sheet specifies them, and route fanout with dog-bone traces or microvias as allowed by your PCB stackup. Keep the cell-voltage sense path as short as possible and connect it close to the battery terminal to minimize IR-drop error under load. Verify stencil aperture design per onsemi packaging guidance for reliable WLCSP solder joint formation.
The I2C bus is the only host interface, so size pull-up resistors for the chosen bus speed and total bus capacitance; typical portable designs use 4.7k to 10k ohm pull-ups to the host rail at 100/400 kHz. Keep SDA and SCL routing short and away from switching regulator nodes and the RF antenna feed used by the host device. Add the decoupling capacitor on the gauge supply pin close to the ball as specified in the data sheet typical application to prevent supply dip reset during transmit bursts.
Do not substitute the LC709209FXE-01TBG footprint with an LC709209FXN-01TBG reel variant without confirming tape orientation per onsemi brochure BRD8011/D, as pick-and-place programming depends on it. The Analog Devices MAX17048 is functionally similar but differently packaged - treating it as a drop-in swap is a common error that forces a PCB respin. Finally, handle WLCSP stock per its moisture sensitivity rating and bake if the floor-life clock has expired to prevent reflow popcorn defects.
Compliance Information
The onsemi LC709209F data sheet ordering table explicitly identifies the LC709209FXE-01TBG device as Pb-Free and Halogen Free. Full REACH and conflict-minerals declarations should be obtained from the official onsemi product page.
