ADI MAX17055: ModelGauge m5 Fuel Gauge
Overview
The MAX17055 from Analog Devices (formerly Maxim Integrated) is a single-cell Li-ion fuel gauge that uses the ModelGauge m5 EZ algorithm to estimate state of charge and remaining capacity. It combines the short-term linearity of a current-based estimator with the long-term stability of an open-circuit-voltage model, and it runs on only about 7 uA. A key selling point of the EZ configuration is that it eliminates the custom battery characterization cycle that older gauges required, which shortens product development. This article covers its verified features, its pack-side implementation, and design notes.
Part Overview
A fuel gauge tracks how much charge remains in a battery so the system can display a percentage and predict run time. The MAX17055 measures cell voltage, current through an external sense resistor, and temperature, then runs the ModelGauge m5 EZ state estimator. The algorithm blends a coulomb-counting-like short-term path, which tracks fast current changes linearly, with an open-circuit-voltage-based long-term model, which corrects drift and accounts for aging, temperature and discharge rate. The EZ variant ships with a default cell model, so the product can start without the lengthy cell characterization used by earlier generation gauges. Data and control are exchanged over a 2-wire I2C bus.Key Features
ModelGauge m5 EZ algorithm for state-of-charge and remaining capacity.
No custom battery characterization required for EZ configuration.
Combines short-term current tracking with long-term voltage-based correction.
Automatic compensation for cell aging, temperature and discharge rate.
Reports SOC in percent and remaining capacity in mAh.
Low 7 uA operating current for long shelf and standby life.
Small wafer-level and DFN packages suited to space-constrained packs.
2-wire I2C host interface.
Key Specifications
Battery support: single-cell Li-ion / Li-polymer
Operating current: about 7 uA (per datasheet)
Algorithm: ModelGauge m5 EZ, hybrid current and voltage estimation
Accuracy: manufacturer testing reports about 97% of tested batteries with error below 3% after a cycle (per Analog Devices design note)
Interface: 2-wire I2C
Sensing: cell voltage, sense-resistor current, and temperature (internal or external thermistor)
Outputs: state of charge percent, remaining capacity mAh, voltage, current, temperature
Packages: small WLP and TDFN options (per datasheet)
(Values per the official MAX17055 datasheet; accuracy depends on cell and initialization.)Applications and Design Notes
The MAX17055 is intended for battery-powered portable devices: smartphones, tablets, wireless headphones, handheld medical and industrial instruments, and any single-cell product that needs an accurate remaining-run-time estimate. It is typically mounted on the battery pack side, close to the cell and the protection circuit, and communicates to the host over the I2C bus.
Design guidance:Use the recommended small-value current-sense resistor between the cell negative and the system ground; its value sets the current measurement range and resolution.
For EZ operation, load the default model and provide the required cell parameters (capacity, sense resistor, termination voltage) through the configuration procedure in the datasheet and vendor software.
Connect a thermistor, or use the internal temperature measurement, so the estimator can apply temperature compensation.
Route the I2C lines with pull-ups to the pack-side voltage, and keep the sense traces Kelvin-connected to the sense resistor to avoid IR errors.
Place the gauge close to the cell so the sensed voltage is not distorted by pack resistance.
Design Considerations and Common Mistakes
The EZ algorithm still needs the correct nominal capacity and sense-resistor values at initialization. Guessing these parameters is the most common cause of a drifting percentage.
A poor sense-resistor layout (shared ground paths, noisy traces) corrupts the current measurement. Use Kelvin sense connections.
The gauge estimates, it does not know the chemistry by magic. For non-standard cells or very high-rate applications, evaluate the accuracy against the actual pack rather than assuming the typical figure.
Because the device lives in the battery pack, shelf-life current matters. The 7 uA operating current is chosen to minimize long-term drain; do not add external loads on the same rail.
Expect the SOC to settle over the first few discharge cycles. The algorithm improves as it observes the cell, so early bench readings are not the steady-state accuracy.
Conclusion
The MAX17055 brings ModelGauge m5 EZ accuracy to single-cell packs while removing the custom characterization step, which is why it is widely used in portable consumer and industrial devices. Its hybrid current-plus-voltage estimator avoids the long-term drift of a pure coulomb counter, and its low 7 uA draw keeps pack drain negligible. The design discipline is in the initialization and the analog layout: correct capacity, a clean sense resistor, and good temperature data are what turn the algorithm into a trustworthy fuel gauge.
FAQ
Q: Does the MAX17055 need a sense resistor?
A: Yes. An external current-sense resistor between the cell and system ground lets the device measure current; its value is part of the EZ initialization.
Q: What is ModelGauge m5 EZ?
A: It is a hybrid fuel-gauge algorithm that uses the linear short-term response of current counting together with the long-term stability of an open-circuit-voltage model, with temperature and aging compensation, and it removes the need for custom cell characterization.
Q: How accurate is the remaining capacity reading?
A: Analog Devices reports that about 97% of tested batteries show less than 3% error after a discharge cycle; real-world accuracy depends on the cell and correct initialization.
Q: Where is the gauge usually mounted?
A: On the battery pack side, near the cell and protection circuitry, communicating to the device host over I2C.
Q: Does it measure temperature?
A: Yes, using an internal temperature sensor or an external thermistor on the pack, which feeds the algorithm's temperature compensation.
For exact specifications and design guidance, refer to the official Analog Devices datasheet for MAX17055:
https://www.analog.com/media/en/technical-documentation/data-sheets/max17055.pdf
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