Power Electronics

Compact Fuel-Gauge ICs Accurately Estimate Li+ Battery State Of Charge

Maxim Integrated Products introduces the MAX17040/MAX17041 and MAX17043/MAX17044 1- and 2-cell fuel-gauge ICs. Using the Company's ModelGauge algorithm, these are the industry's only fuel gauges that accurately estimate the state of charge (SOC) of a Li+ battery without requiring current sensing. ModelGauge ICs eliminate the current-sense resistor and require very few external components, thus saving both space and cost. Because of their simplicity, low implementation cost, and small size, these ICs are ideal for handheld 1- and 2-cell Li+ battery applications like wireless handsets, smartphones, e-books, portable game players, digital cameras, handheld computers and financial terminals, portable navigation equipment, and portable medical equipment.

Traditional Li+ battery fuel gauges are mounted inside the battery pack and require multiple supporting discrete components, including a sense resistor. To provide the estimation of battery capacity, they rely on coulomb counters, which must then be calibrated--another added cost. Yet, coulomb counters also have a problem with even small ADC offset errors that accumulate indefinitely. To correct for these drifts, the battery must go into full, empty, or standby states on a regular basis.

Some recent design advances have enabled implementation of the fuel-gauging function on the system side, instead of inside the battery pack. While this approach reduces the cost of the application somewhat, it has little effect on the board area.

Finally, most price-sensitive applications save cost by measuring the battery voltage and using a simplistic lookup table, which results in unreliable SOC estimation (30% to 40% error), as load variations, temperature effects, and aging are not accounted for properly. Because of this, many system designers are barely comfortable showing even three to four bars to indicate battery state.

Maxim's ModelGauge technology overcomes the limitations of voltage-only-based fuel gauging. The MAX17040/MAX17041 and MAX17043/MAX17044 ICs' sophisticated battery-modeling scheme provides excellent accuracy with very few external components.

Finally, these ModelGauge ICs can be mounted on the system-side, instead of the battery pack. This allows the system manufacturer to control all costs, and minimize the complexity of supply-chain constraints, and reduces the expense of the battery pack

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