A Wireless Power Interface for Rechargeable Battery Operated Medical Implants

• Published in: IEEE transactions on circuits and systems. II, Express briefs Vol. 54; no. 10; pp. 912 - 916
• Main Authors: Pengfei Li, Bashirullah, R.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2007; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Batteries; Battery; Battery charger; Charging; Circuits; CMOS technology; Comparators; Electric batteries; Electric potential; Implants; Lithium; Low voltage; Medical; medical implants; rechargeable lithium (Li)-ion battery; Resistors; Schottky barriers; Schottky diodes; Signal resolution; Surgical implants; Transplants & implants; wireless power interface
• ISSN: 1549-7747; 1558-3791
• DOI: 10.1109/TCSII.2007.901613

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-mum 3M-2P CMOS technology indicate that plusmn1.3% (or plusmn20 muA) EOC accuracy can be obtained under worst case conditions for a comparator offset voltage of plusmn5 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%.