Patent ID: 7501794

Claim:
A semiconductor device comprising: an adjustable current source; an interface to an external battery, the interface coupled to the adjustable current source, the external battery responsive to current supplied by the adjustable current source via the interface; a feedback control module having a first input responsive to a voltage level at the external battery and a second input responsive to a limit voltage, and having an output directed to control the current supplied by the adjustable current source; and wherein the feedback control module is configured to operate in a first phase of a charging cycle in which a constant current is applied to the external battery from the start of charging to when an upper threshold voltage level of the external battery is reached without tinning off the constant current, and wherein the feedback control module is configured to operate in a second phase of a charging cycle wherein the feedback control module selectively provides a signal to turn off the current supplied by the adjustable current source, wherein a first voltage at the external battery is measured during a time period when the current is turned on and a second voltage at the external battery is measured during a time period when the current is turned off, and wherein the feedback control module provides the signal to turn off the current when a difference between the first voltage and the second voltage is less than a threshold value.