A method and circuit for simultaneously charging a battery and providing
supply voltage to a load. The circuit includes a low-drop-out voltage
(LDO) regulator and a constant-current, constant-voltage (CC-CV)
regulator. In one embodiment, CC-CV regulator provides a control voltage
to the LDO regulator generated by a voltage-controlled current source. As
charge voltage approaches battery termination voltage, the control
voltage is reduced regulating LDO regulator output to provide constant
voltage while decreasing charge current to the battery. In another
embodiment, a slow response amplifier and a current mirror in the CC-CV
regulator provide a smooth and stable charging current to the battery
that is decreased as battery charge approaches a full charge level, while
maintaining constant supply voltage to the load. In a further embodiment,
an externally programmable amplifier in the CC-CV regulator may enable
use of the circuit with varying power sources.