An implantable
medical device, such as an implantable
pulse generator (IPG) used with a
spinal cord stimulation (SCS)
system, includes a rechargeable lithiumion battery having an
anode electrode with a substrate made substantially from
titanium. Such battery construction allows the rechargeable battery to be discharged down to zero volts without damage to the battery. The implantable
medical device includes battery charging and protection circuitry that controls the charging of the battery so as to assure its reliable and
safe operation. A multi-rate charge
algorithm is employed that minimizes charging time while ensuring the
battery cell is safely charged.
Fast charging occurs at
safer lower battery voltages (e.g.,
battery voltage above about 2.5 V), and slower charging occurs when the battery nears full charge higher battery voltages (e.g., above about 4.0 V). When potentially less-than-safe very low voltages are encountered (e.g., less than 2.5 V), then very slow (
trickle) charging occurs to bring the
battery voltage back up to the
safer voltage levels where more rapid charging can safely occur. The battery charging and protection circuitry also continuously monitors the
battery voltage and current. If the battery operates outside of a predetermined range of
voltage or current, the battery protection circuitry disconnects the battery from the particular fault, i.e. charging circuitry or load circuits.