Design of AFE and PWM Drive for Lithium-Ion Battery Management System for HEV/EV System

This paper describes Analog-front-end (AFE) for lithium-ion battery management system. It includes the design of the differential clocked comparator which compares the cell voltage and the external reference voltage in the cell voltage domain to find if the cell voltage is within the safe operating range. This also includes PWM drive for the external fly-back dc-dc converter, the charge shuttling switches and control logic for active cell balancing of Lithium-ion battery cells in 0.35um high voltage (HV) CMOS technology. PWM drive circuit generates programmable frequency and programmable duty cycle to drive external low-side FET in the primary of the fly-back dc-dc converter. Secondary of the fly-back converter is connected to on-chip charge shuttling switches. Based on the differential comparators decision for the set target cell balance voltage, the digital finite state machine (FSM) generates control signal to charge individual cells in the battery sequentially. These circuits are part of lithium-ion battery cell balancer IC. The IC is designed to support cell voltage monitoring and cell balancing of a lithium-ion battery of seven cells.