AN817
Vishay Siliconix
A Discrete Approach to Battery Charging for Cellular Phones
Guy Moxey and Michael Speed
INTRODUCTION
All portable cordless appliances must receive power from an external source, whether it’s a wall cube adapter, car charger, or docking station. This external source will then charge, in a predetermined fashion, the equipment’s internal battery. In the case of a portable phone, the power management system will incorporate charging control circuitry to regulate the voltage supplied to the battery from the external charger. External charging equipment- whether wall cubes or chargers that utilize car cigarette lighters- will supply a continuous but unregulated voltage to the phone, typically 4.2 V for a single Lithium-ion (Li+) cell. A typical charging design is explored in Appendix A. Charge control for a Li+ cell is most monly implemented by a discrete MOSFET in series with a Schottky diode, controlled via the onboard power management ASIC or system microprocessor....
