Charger power switch for mobile phones

A battery charging control IC has been developed in third-generation BCD technology and the experimental results of its typical application are described. The device consists of a fully integrated 300 mW power switch connected between the battery-charger and the battery. It has to protect the phone from high voltage spikes caused by battery-charger plug connection and disconnection, or those entering the charger via the mains or from the car battery. To eliminate audio and RF band interference problems in the phone, a new circuit for a soft switching has been implemented allowing a controlled slew-rate of the charging current. Moreover, the device is protected when a charger reverse polarity occurs; for this reason the integrated power switch connected between the battery-charger and the battery consists of two DMOS transistors in "back to back" configuration to avoid the battery discharge. The device has two different operation modes: it works like a current regulator when the battery is completely discharged, providing a lower current than the charger one, and like a low value resistance switch when the battery voltage is high enough to power up the phone. The IC includes other functions such as programmable externally output voltage protection, input transient voltage protection and thermal protection.