Battery Fuel Gauge Reference Design 

The design enhances battery fuel gauge accuracy for low-power IoT applications, integrating wireless connectivity, automatic pairing, and efficient power management.

The TIDA-01014 reference design from Texas Instruments (TI) features a high-accuracy battery fuel gauge for low-power applications like Bluetooth-enabled wireless IoT field metering devices. It enhances the wireless digital multimeter (DMM) reference design by improving fuel gauge resolution and accuracy while showcasing the state-of-battery reporting capabilities of the bq27426 fuel gauge. The design also integrates TI’s NFC Bluetooth automatic pairing and CapTIvate capacitive touch technologies.

With the rise of battery-powered IoT sensors, industrial field instruments and data acquisition (DAQ) systems require reliable remote monitoring. Advances in sensor technology and low-power connectivity, such as TI’s solutions, now enable these instruments to function as wireless battery-powered systems, improving cost efficiency, deployment, and reliability. As a result, effective battery management has become crucial, particularly in tracking the battery’s state of charge (SoC). TI’s bq27426 fuel gauge, originally designed for higher-power applications, also supports lower-power sensor nodes, as demonstrated in this reference design.

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The TIDA-01014 improves fuel gauge accuracy by enhancing coulomb measurement resolution through an increased sense resistor and adjustments to the bq27426 discharge profile parameters. The system-side Impedance Track™ feature provides key battery metrics, including remaining capacity, average current, voltage, power, and SoC. Additionally, it calculates and reports “time remaining” based on these parameters.

To demonstrate these capabilities, the design uses an LIR2477 Li-Ion coin cell battery instead of the AAA Li-Ion battery in the TIDA-01012 design. This 3.7-V, 150-mAh coin cell better represents batteries typically used in sensor and field metering applications. The bq27426 determines battery state using impedance tracking and coulomb counting, both of which depend on accurate current measurement.

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The bq27426 is a single-cell battery gauge with a pre-programmed chemistry profile that accurately predicts the capacity and operational characteristics of a Li-based rechargeable cell using patented Impedance Track technology. A system processor can query the device for battery information, including state of charge (SoC).

It offers three selectable pre-programmed profiles for 4.20-V, 4.35-V, and 4.40-V cells. The gauge reports remaining capacity and SoC with a smoothing filter, automatically adjusting for battery aging, self-discharge, temperature, and rate changes while estimating state-of-health. It supports a 400-kHz I²C serial interface.

The CC2640 is a wireless MCU designed for Bluetooth Low Energy applications. As part of the CC26xx family, it offers cost-effective, ultra-low-power 2.4-GHz RF performance. Its low active RF and MCU current consumption enable long battery life, making it suitable for small coin cell batteries and energy-harvesting applications.

The device features a 32-bit ARM Cortex-M3 processor running at 48 MHz, along with a rich set of peripherals, including an ultra-low-power sensor controller. This controller autonomously collects analog and digital data while the rest of the system remains in sleep mode, making it ideal for applications requiring long battery life and a compact form factor.

TI  has tested this reference design. It comes with a bill of materials (BOM), schematics, assembly drawing, printed circuit board (PCB) layout, and more. The company’s website has additional data about the reference design. To read more about this reference design, click here.