MAX38889 2.5V to 5.5V, 3A Reversible Buck/Boost Regulator for Backup Applications Functional Diagram BACKUP ENB ENABLE BOOST CONTROLLER SYS VSYS (MAIN SUPPLY) C DISCHARGE CHARGE SYS ISET CURRENT LX LIMIT L CAP V R CAP ISET MUX R1 C1 CSC SUPER BUCK CAP CHARGE ENC CONTROLLER PGND ENABLE R2 R6 C2 0.5V FBCR R3 R7 FBCH 1.2V R8 R9 FBS R4 BKB BACKUP MODE CONTROL RDY CAP READY C4 0.5V MAX38889Detailed Description The MAX38889 is a flexible storage capacitor or capacitor bank backup regulator transferring power efficiently between a storage element and a system supply rail. When the main supply is present and its voltage is above the minimum threshold system supply voltage, the regulator operates in charging mode and charges the storage element with a maximum 3A peak, 1.5A average inductor current. Once the storage element is charged, the circuit draws only 4µA of current while maintaining the storage element in its ready state. The supercapacitor needs to be fully charged to enable backup operation. When the main supply is removed, the regulator prevents the system from dropping below the set system backup operating voltage, boosting the supercapacitor voltage to a regulated VSYS by discharging the storage element with a maximum 3A peak inductor current. During this backup mode of operation, the MAX38889 utilizes an adaptive on-time, current-limited, pulse-frequency-modulation (PFM) control scheme. Once the MAX38889 is in backup mode, the BKB flag is low. The external pins allow various settings such as maximum supercapacitor voltage, system backup voltage (VSYS), and peak inductor charge and discharge current. www.maximintegrated.com Maxim Integrated | 9 Document Outline Product Highlights Key Applications Simplified Application Diagram Pin Configuration Absolute Maximum Ratings Package Information Electrical Characteristics Typical Operating Characteristics Pin Configuration Pin Descriptions Functional Diagram Detailed Description Application Circuits Supercapacitor Voltage Configuration System Voltage Configuration Charge/Discharge Current Configuration Charging Backup Applications Information Capacitor Selection Supercapacitor Selection Inductor Selection Status Flags BKB Flag RDY Flag Enabling the Device Charger Enable Input (ENC) Backup Enable Input (ENB) PCB Layout Guidelines Ordering Information
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