Monolithic Lithium Battery Charge Management Chip Design

With the development of modern electronic technology, electronic devices tend to be portable. This trend also made their batteries portable and efficient. Lithium-ion battery with its high energy power density, high power supply voltage, no memory effect, no pollution gradually replace the traditional nickel-cadmium, nickel metal hydride batteries, lead acid batteries are widely used in modern portable electronic products. Compared with other chemical batteries, lithium-ion batteries have excellent performance and also more delicate and fragile therefore the charging process must be strictly controlled. They require high accuracy voltage and current settings, different charging mode and comprehensive protection circuitry.This paper designed a current control model PWM switching power supply chip. It is suitable for the charging management of all kinds of lithium batteries. In order to ensure efficient charging and energy saving, this chip offers constant current mode, constant voltage mode and BURST mode. When the completely released lithium-ion battery is placed in chip as its load, the system automatically detects and chooses a larger constant current to charge the battery. At this stage, duty cycle is constant and the operating frequency increased as the battery voltage rises. When the battery voltage approaches the termination value, the chip enters into constant voltage charging mode. The system began to reduce the duty cycle, the charging current also reduces. At this stage chip works in the same frequency. When battery voltage reaches the termination value, the system will shut down in order to prevent battery damage caused by its overshoot. When the battery voltage falls for some reason, the system automatically enters BURST mode. The chip work with lower frequency, lower current to complement battery energy slowly. Cycle-by-cycle current limit, OVPT and UVLO circuit are built-in the chip to ensure the safe operation of chips.Firstly, this paper characteristic of lithium-ion battery and a brief description of the principle of switching power supply; secondly, introduced each module of the system and for the key modules we give the design process and simulation results; finally, each operating mode and the overall operation of the chip are simulated. This chip is build on CSMC 0.5um BCD process and used in the simulation is Cadence Spectre simulation tools.