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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 4520
Maxim > Design Support > Technical Documents > Application Notes > Battery Management > APP 4520
Keywords: lithium-battery chargers, charge-termination voltage, fast charge, dual op amp
APPLICATION NOTE 4520
Charging Lithium Batteries with a Nonstandard
Termination Voltage
By: Shasta Thomas, Applications Engineer
Jul 05, 2011
Abstract:
By adding
a dual op amp and some other components to a lithium-battery-charger IC, you can
adjust the charging voltage to any level within the range for standard lithium batteries (3.6V to 4.2V).
A similar version of this article appeared in the March 31, 2008 issue of EE Times magazine.
Lithium batteries have been produced over the years by many manufacturers, and they have settled into a
fairly standard product—one with a maximum charge voltage of 4.2V ±1%. As a result, most of the ICs
currently available for charging lithium batteries are designed to charge at 4.2V, with a tight tolerance of
±1%.
In the past few years, however, a different lithium-battery technology has reached the market, offering
higher power density, accepting much higher charge and discharge rates than standard batteries, and
featuring various charge-termination voltages. This design idea modifies the application circuit of a
standard, high-end IC charger to provide a different termination voltage and higher current rate, while
maintaining all the charger's original features.
The battery to be charged in this case is type ANR26650m1, manufactured by A123 Systems. It accepts a
standard charge mode at 3A (1.3C), and can be fast-charged at 10A (4.34C) with a charge-termination
voltage of 3.6V. Thus, it represents the battery types whose termination voltages range between 4.2V and
3.6V. The circuit of Figure 1 is a modification of the application circuit for an IC designed to charge from
one to four 4.2V lithium cells (MAX1737). By adding a micropower dual op amp (MAX4163) and some
resistors, this modification allows you to charge 3.6V cells.
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