Method and apparatus for measuring battery charge and discharge current using a direct analog-to-digital conversion of a charge/discharge replica current

Abstract

Disclosed is a method for charging a battery and circuitry for performing the method. The method includes steps of: (A) generating at a first node a battery charge current (Icharge) for charging the battery; (B) generating at a second node a replica current (Irep) from Icharge, where Irep<Icharge; and (C) operating a closed loop current sink for sinking Irep, where a digital output of said closed loop current sink is a measure of the magnitude of Icharge. In the preferred embodiment the digital output is input to a control circuit for controlling the generation of Icharge. Also in the preferred embodiment the closed loop current sink is constructed from a multi-stage DAC that is driven by an output of an n-level digital filter that is incremented or decremented as a function of a voltage difference between the first node and the second node. Preferably the multi-stage DAC is a multi-stage current steering DAC, and the n-level digital filter is constructed using an up/down counter. A selection of stages of the multi-stage DAC to be turned off and on is made by a DEM logic block that is interposed between the output of the counter and the multi-stage DAC. The disclosed circuitry and method may be extended for providing a battery discharge measurement circuit for enabling a battery capacity test to be performed.