A wireless power interface for rechargeable battery operated medical implants

This brief presents a highly integrated wirelessly powered battery charging circuit for miniature lithium (Li)-ion rechargeable batteries used in medical implant applications. An inductive link and integrated Schottky barrier rectifying diodes are used to extract the dc signal from a power carrier while providing low forward voltage drop for improved efficiency. The battery charger employs a new control loop that relaxes comparator resolution requirements, provides simultaneous operation of constant-current and constant-voltage loops, and eliminates the external current sense resistor from the charging path. The accuracy of the end-of-charge (EOC) detection is primarily determined by the voltage drop across matched resistors and current-sources and the offset voltage of the sense comparator. Experimental results in 0.6-mu m 3M-2P CMOS technology indicate that +/- 1.3 % (or +/- 20 mu A) EOC accuracy can be obtained- under worst case conditions for a comparator offset voltage of +/- 5 mV. The circuit measures roughly 1.74 mm(2) and dissipates 8.4 mW in the charging phase while delivering a load current of 1.5 mA at 4.1 V (or 6.15 mW) for an efficiency of 73%.