A low power battery management system for rechargeable wireless implantable electronics

An integrated battery management system for low power wireless implantable electronics is presented herein. The system is designed for miniature implantable Li-ion rechargeable batteries with limited cell capacity and 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 detection is primarily determined by the voltage drop across matched resistors and current-sources and the offset voltage of the sense comparator. Preliminary simulations in 0.5mum bulk CMOS technology indicate that plusmn1% (or plusmn15muA) end-of-charge accuracy can be obtained under worst-case conditions for a comparator offset voltage of plusmn5mV. The proposed battery control loop measures roughly 170mum by 960mum and dissipates approximately 150muWatts