Circuitry useable to protect and reliably charge a rechargeable battery, evenfrom a zero-volt state, is disclosed, and is particularly useful when employedin an implantable medical device. The circuit includes two charging paths, afirst path for trickle charging the battery at a relatively low current whenthe battery voltage is below a threshold, and a second path for charging thebattery at relatively higher currents that the battery voltage is above acertain threshold. A passive diode is used in the first trickle-charging pathwhich allows trickle charging even when the battery voltage is too low forreliable gating, while a gateable switch (preferably a PMOS transistor) isused in the second higher-current charging path when the voltage is higher andthe switch can therefore be gated more reliably. A second diode between thetwo paths ensures no leakage to the substrate through the gateable switchduring trickle charging. The load couples to the battery through the switch,and preferably through a second switch specifically used for decoupling theload.
