Charging EnerChips

As with other rechargeable batteries, discharge capacity and cycle life are a function of charge voltage, discharge cutoff voltage, depth-of-discharge, temperature, and other factors.

The system designer must understand the effect of these factors when designing the charge control circuit.

Guidelines:

• Never apply more than 4.3V across the battery terminals. There is no need to externally limit the charging current of small surface-mount batteries. The intrinsic cell resistance is sufficient to limit the current to an acceptable level as long as the applied voltage does not exceed 4.3V.
• The charging voltage and charge time determine the amount of charge delivered to, and accessible from, the battery. A higher charging voltage will deliver more charge, but will also result in greater long-term capacity fade as a function of charge/discharge cycling.
• The rechargeable batteries may be charged at a constant current (CC) followed by a constant voltage (CV). During the CC phase, the current may be set to any value that results in an acceptable charging time and does not cause the battery voltage to exceed 4.3V.
• CV charging will normally result in faster charging times than the combined CC-CV approach. Please refer to the data sheets of these batteries.
• The range from 4.1V to 4.0V is also acceptable, but the EnerChip will not attain a full charge.

Charge Circuits:

EnerChip thin film rechargeable batteries are conducive to a variety of charge control circuits. Circuits as simple as one or more diodes and a fixed power supply may be used in the most cost sensitive applications. However fluctuations in the power supply voltage and part-to-part variability in the diode voltage drop will affect the voltage across the battery terminals. In some cases a diode may be needed to meet a system supply voltage requirement or to prevent the battery from discharging through the power supply line when main power is lost. The reverse bias leakage of the diode must be very low. For more information and charging circuit design examples for EnerChip batteries, consult AN-1002 titled, ‘Guidelines for Charging Cymbet Batteries’ on the Applications Note Note page.