This application note explores how to implement the parallel operation of buck-boost converters using the LM51772 Buck-Boost Controller IC. The LM51772 is designed to handle a wide range of input voltages and can operate in buck, boost, or buck-boost modes, making the device a flexible choice for various power supply designs. When higher output currents or system redundancy are needed, using multiple LM51772 controllers in parallel can be an effective design. This document guides users through the practical steps of setting up parallel operation with the LM51772, focusing on key factors like verify the controllers share current evenly, maintain loop stability, and manage heat dissipation. This application note also addresses the challenges of parallel operation, particularly the potential for current-sharing errors, and offers practical advice on reducing these errors. Real-world design examples, simulation results, and experimental data are presented to demonstrate the effectiveness of the proposed configurations.
By following the guidelines in this application note, designers can optimize power delivery and verify reliable operation in demanding power conversion applications.
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The LM51772 device is a wide input voltage range, four-switch buck-boost controller IC with integrated drivers for N-channel MOSFETs.
One single LM51772 converter can deliver power greater than 200 W. To get higher output power, parallel power stages are needed to solve the excessive board heating problem because of the increased switching and conduction losses. Parallel operation of power stages can also provide many other benefits like: enhanced modularity, design flexibility, and minimized component ratings. These benefits can be realized only if the LM51772 converters evenly share the total load power. This application report shows how to configure and interconnect the LM51772 devices to get a well-balanced load-sharing. Test results show less than a 10% error in load sharing without sacrificing the overall performance.