National Semiconductor Corporation introduced a cost-effective, high precision CVCC (constant voltage, constant current) charge controller that improves the run-time of the single- and dual-cell lithium-ion battery packs used to power hand-held electronic devices. The LM3622 precisely controls charge and end-of-charge voltage and current from a current-limited DC-DC switching charger or linear charger. In the A-grade configuration, the LM3622 is rated at 0.6% regulation, which is twice the accuracy of directly competitive products.

"Designers of hand-held electronic equipment are committed to maximizing the run-time of lithium-ion battery packs," said Venkatesh Shan, National's director of marketing for power management products. "Batteries charged with CVCC chargers that use the LM3622 will reach full capacity and have longer run time due to the part's improved precision. In addition, the high integration will reduce cost and board space."

National's LM3622 is functionally equivalent to the Mitsumi MM1332, but offers the added benefits of improved voltage regulation accuracy and selectable end-of life voltage in an SO-8 package. With its extra pin-select feature, the LM3622 gives designers a choice of 2.7V or 2.15V end-of-life detection voltages. Moreover, maximum battery capacity is attained without the need for external precision resistors.

The LM3622's architecture is based on high-gain constant voltage, constant current control loops, which are well suited to pole splitting lead-lag compensation techniques. In its simplest form, an application circuit using National's charge controller requires only four inexpensive components. The external PNP transistor, controlled by the LM3622, provides charge current to the battery from an external DC power source. The controller draws only 200nA from the battery when the charger is disconnected, preventing discharging of the battery pack.

The LM3622 operates with DC sources ranging from 5 volts to 28 volts. In addition, the LM3622 offers pin-selectable charge termination voltages for either coke (4.2V) or graphite (4.1V) anode chemistry.

This part is directly based on the Mitsumi MM1332 and has added some dramatic improvements to, quite clearly, entice a lot of design wins to Santa Clara. That is also clear from the vigorous pricing that has been adopted. Certainly the additional features make the controller a lot smarter than it was and that adds considerable value to the user in terms of maximizing battery life and, immediately, maximizing run time for any particular application. Run time is, again and again, the most demanded specification by the consumer who is willing -- knowingly or unknowingly -- to give up features or performance in a product. The selectable end-of-life, in particular, will allow the designer to choose a voltage where his design will still operate rather than approximate.