A 3.7-V 100-mA Dual-Loop CC/CV Lithium-Ion Battery Charger With Programmable Current Regulation and Voltage Buffer

Abstract

A hybrid based CC/CV dual loop system continues to remain the most effective approach for Li-Ion batteries charging for many applications. However, issues with adjustable regulators used in constant current circuits and error amplifiers for constant voltage pose risks to sufficient operation. This paper describes a novel design of a charging mechanism for Li-Ion batteries rated at 1C and 100 m - 500 mAh via a CC/CV dual loop feedback circuit, to manage a regulated current of 100 mA with a maximum 3.7 terminal voltage. The constant current circuit implements a programmable current source adjusted with external resistor ratios, RC network for noise reduction in the 10 Hz-100 kHz bandwidth range, and a supplementary series resistor to dampen resonant ringing against parasitic reactance. The method for constant voltage uses an error amplifier with negative feedback and reference from a 3 resistor divider for a reduced 8 mA current draw and designated voltage output for error detection. The output is then chained to a voltage buffer with high input and low output impedance for stability and high current isolation before leading to a MOSFET pass element handling battery charging, with regulation procedures when nearing the terminal voltage of 3.7 V. Moreover, onboard power input is 5 V regulated from the external powering device.