The Maxim MAX17201 Single-Cell Stand-Alone Fuel Gauge IC

Implementing single-cell pack-side battery gauges in portable devices is now easier and more secure with the MAX17201 from Maxim Integrated Products. The MAX17201 is an ultra-low-power (consuming 9 µA quiescent current and just 18 µA in active mode), single-cell, stand-alone fuel gauge IC that implements the Maxim ModelGauge™ m5 algorithm without requiring host interaction for configuration. This feature makes the MAX17201 an excellent choice for a single-cell pack-side fuel gauge.

Figure 1: Maxim’s ModelGauge™ m5 secure stand-alone fuel gauge requires no battery customization.

MAX17201 operation overview

Fuel gauging can be difficult because battery voltage varies with temperature and load, while coulomb-counting requires sophisticated compensation to eliminate offset accumulation errors. The MAX17201 provides precision measurements of current, voltage, and temperature. The temperature of the battery pack is measured using an internal temperature measurement and up to two external thermistors supported by ratiometric measurements on auxiliary inputs. The sophisticated ModelGauge m5 algorithm converts these raw measurements into accurate values for state-of-charge (SOC), absolute capacity (mAh), time-to-empty, and time-to-full (while charging); all of which improve the user experience of the host device while enabling maximum run-time. Additionally, the MAX17201 provides for programmable alert functions for voltage, temperature, current, and SOC. A 2-wire I²C interface provides access to this data and to control registers.

Furthermore, the ModelGauge m5 algorithm automatically compensates for cell aging, temperature and discharge rate, and provides accurate SOC in mAh or percentage over a wide range of operating conditions. The algorithm combines the short-term accuracy and linearity of a coulomb-counter with the long-term stability of a voltage-based fuel gauge, along with temperature compensation to provide highly accurate fuel gauge data.  Also, the algorithm does not suffer from abrupt corrections that normally occur in coulomb-counter algorithms, since tiny continual corrections are distributed over time.

Accurate end-of-life calculation

Battery packs generally need to be replaced every few years—when batteries age, their characteristics change over time and no longer provide adequate run-time. As batteries age, the cell approaches empty and the fuel gauge error always converges to 0%. As the battery approaches this critical region, the ModelGauge m5 algorithm invokes a special error correction mechanism that eliminates any error. The algorithm detects the smallest changes in the capacity of the battery to more accurately predict how long the battery will last before the capacity degrades rapidly. The MAX17201 provides an accurate estimation of time-to-empty and time-to-full, Cycle+™ age forecast, and three methods for reporting the age of the battery: reduction in capacity, increase in battery resistance, and cycle odometer. This age forecasting gives system designers the ability to adjust charger parameters to extend the battery life, or to plan a timely replacement of the battery.

Design benefits

To ease in the design process, the ModelGauge m5 EZ configuration eliminates the time and resource-consuming characterization and calibration processes for a large number of battery types. There is no need to reset the device to track battery usage correctly since it learns the capacity without the battery going to the full, empty, or relaxed states. This gives the projects that incorporate the MAX17201 a faster time-to-market.

Designers can learn more about how the IC works and if it would be suitable for their applications with the MAX17201 ModelGauge™ Series Power Management, Fuel Gauge Evaluation Board (Figure 2). The MAX17201G evaluation kit is a fully assembled and tested surface-mount PCB that evaluates the stand-alone ModelGauge m5 pack-side fuel gauge IC for lithium-ion batteries in handheld and portable equipment. The evaluation kit includes the Maxim DS91230+ USB interface, IC evaluation board, and RJ-11 connection cable. The Windows®-based graphical user interface (GUI) software (requires a Windows 7 or newer operating system) is available for use with the evaluation kit and can be downloaded from Maxim’s website.

Figure 2: Maxim’s MAX17201 ModelGauge Series Power Management, Fuel Gauge Evaluation Board

Advanced security

Another added feature that the MAX17201 has is enhanced security against creating counterfeit products. To prevent battery pack cloning, the ICs integrate SHA-256 authentication with a 160-bit secret key. Every IC also incorporates a 64-bit unique identification number (ROM ID). So if battery-pack security is something that is desired for an application, this device would fit the bill nicely.

Applications

The MAX17201 is ideal for any rechargeable battery-operated device such as wearables, drones, tablets, smartphones, portable game players, e-readers, digital still and video cameras, handheld computers and terminals, portable medical equipment, handheld radios, and other IoT applications.