A high-precision low-drop linear regulator for battery charging application

A linear voltage regulator for lithium-ion battery charging application is presented. This circuit is part of a power management chip implemented in a standard BiCMOS technology within a chip set for GSM phone handsets. For this application a low-drop regulator configuration with external p-channel power MOSFET is required. A new technique is proposed in order to achieve a specified accuracy with limited loop gain. Stability of the regulator is ensured over a wide range of the load current by carefully shaping the regulator´s frequency transfer function. The regulator performs a limitation of the gate-source voltage of the external MOSFET, even though the technology does not provide zener diodes. Thanks to an inherent suppression of line voltage variation, the total error of the output voltage over all modes of operation is only 1.5%, which is necessary for charging Li-Ion batteries. The regulator occupies an area of 0.4 mm²in a 0.5 µm BiCMOS technology.