Bidirectional Buck or Boost DC-DC Converter – Reference Design

February 15, 2020 by Paul Shepard

Demonstration circuit 2351A from Analog Devices is a high voltage, high efficiency synchronous buck or boost dc-dc converter. It is designed to have 36V to 56V on one side and 8V to 14V on the other side. It can supply a 35A maximum output current in buck mode and delivers 7A of current in boost mode. The demo board features the LT8228EFE controller. This part can seamlessly transition from bucking to boosting.

With built-in circuit breaker function and other protection features, the LT8228 is designed for high reliability systems requiring N+1 redundancy or other protections in industrial, automotive, medical, military, and avionics applications.

The DC2351A is designed to be paralleled with other DC2351A boards to increase the total output current. With adequate heatsinking or airflow, the output current can be increased.

About the LT8228

The LT8228 is a 100V bidirectional constant-current or constant-voltage synchronous buck or boost controller with independent compensation network. The direction of the power flow is automatically determined by the LT8228 or externally controlled. The input and output protection MOSFETs protect against negative voltages, control inrush currents and provide isolation between terminals under fault conditions such as switching MOSFET shorts.

In buck mode, the protection MOSFETs at the V1 terminal prevents reverse current. In boost mode, the same MOSFETs regulate the output inrush current and protects itself with an adjustable timer circuit breaker.

The LT8228 offers bidirectional input and output current limit as well as independent current monitoring. Masterless, fault tolerant current sharing allows any LT8228 in parallel to be added or subtracted while maintaining current sharing accuracy. Internal and external fault diagnostics and reporting are available via the FAULT and REPORT pins. The LT8228 is available in a 38-lead TSSOP package.

Summary of LT8228 features

  • Bidirectional Voltage or Current Regulation
  • Bidirectional Reverse Current Protection
  • Input and Output Negative Voltage Protection to -60V
  • Bidirectional Inrush Current Limit and Boost Output Short Protection
  • Switching MOSFET Short Detection and Protection
  • 10V Gate Drive
  • Wide Input and Output Voltage Range Up to 100V
  • Feedback Voltage Tolerance: ±1.0% Over Temperature
  • Bidirectional Programmable Current Regulation and Monitoring
  • Extensive Self-Test, Diagnostics and Fault Reporting
  • Programmable Fixed or Synchronizable Switching Frequency: 80kHz to 600kHz
  • Programmable Soft-Start and Dynamic Current Limit
  • Masterless, Fault Tolerant Current Sharing