National Semiconductor recently introduced two battery-charging products for portable electronics, a single-cell USB/AC charger, and a charge control and protection circuit for embedded Lithium-Ion and Lithium-Polymer batteries. Ideal for small portable devices, these ICs require few external components and support up to 1,2 A full-rated current.
The LP3947 charge management system and LM3655 battery protection IC offer extensive battery over-voltage and over-current protection, battery pre-conditioning and 1% charger voltage accuracy. They are packaged in a small thermally-enhanced leadless leadframe (LP3947) and a very small micro SMD (LM3655).
Charge manager
The LP3947 is a complete charge management system that safely charges and maintains a Li-Ion battery from either a USB power source or an AC adaptor. Using the USB power source, the LP3947 supports both low-power or high-power charging. Alternatively, the LP3947 can take a charge from the AC adaptor. For the USB power source or AC adaptor, the charge current, battery regulation voltage and end-of-charge point can be selected via an I²C compatible interface.
The LP3947 can also operate on default values that are pre-programmed in manufacturing. The battery temperature is monitored continuously at the temperature sensor pin to safeguard against hazardous charging conditions. The charger also has under-voltage and over-voltage protection, as well as an internal 5,6-hour timer to protect the battery. The pass transistor and charge current-sensing resistor are all integrated inside the LP3947.
The LP3947 operates in four modes: pre-qualification, constant current, constant voltage and maintenance. There are two open-drain outputs for status indication. An internal amplifier readily converts the charge current into a voltage. The charger can also operate as a linear regulator, providing a maximum of 1,2 A to the load.
Battery charge and protection
The LM3655 provides complete charge control, discharge control and battery safety of a single Li-Ion cell. It supports battery charging by using a variety of power supply types including unregulated current-limited wall adopters, regulated wall adopters and vehicle power adopters. Charge current control is achieved using an external bipolar PNP power transistor.
The LM3655 provides effective and comprehensive discharge control functionality. The operating load current is supplied by the Li-Ion battery and passes through the IC device. This allows the battery power to disconnect due to overload, short-circuit or low battery conditions. The IC also offers extensive battery safety protection against over-voltage and over-current. The internal safety circuit is backed up by an identical circuit to provide safety redundancy.
For more information contact Simon Churches, Arrow Altech Distribution, +27 (0)11 923 9600, schurches@arrow.altech.co.za
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