Abstract

The LM5177 is a 4-switch buck-boost converter that supports seamless bi-directional operation, designed for applications like critical system power backups and energy storage from renewable sources. This application note provides a comprehensive guide on setting up the bi-directional current feature of the LM5177, offering clear design guidelines to help users get the most out of the device and optimize the performance in various scenarios. In Battery Backup mode, energy storage connected to the Vin of the LM5177 is charged with a constant current, managed by the built-in current limit features of the device and an external circuit using the TLV431 shunt regulator.

The TLV431 is used for limiting the charging voltage and controls the MODE pin with switching the converter between FPWM and PSM modes to maintain the desired storage voltage with minimal fluctuations. Tests using the LM5177 Buck-Boost Controller Evaluation Module show smooth transitions between constant current and constant voltage charging, with only minor ripple due to mode switching delays. The low operating current and reference voltage boost efficiency of the TLV431, and further adjustments to the MODE pin controller can enhance performance even more.

Overall, the capabilities of the LM5177 and the outlined control strategies offer a reliable design for efficient energy storage and management for a wide range of applications.