LT8228 – 100 V Bidirectional Buck or Boost DC/DC Controllers with Protection

Analog Devices’ LT8228 100 V bidirectional buck or boost DC/DC controllers provide sustainable power in hybrid and electric vehicle (EV) critical non-drive train subsystems by controlling 48 V and 12 V batteries with bidirectional capabilities allowing for power source redundancy. These controllers also enable full functional safety if one of the batteries fails by forcing the other battery to take over allowing the vehicle to function properly, avoiding potential catastrophic results.

The LT8228 automatically determines the direction of power flow, or the direction can be externally controlled. Input and output protection MOSFETs protect against negative voltages, control inrush currents, and provide isolation between terminals under fault conditions such as shorts in the switching MOSFETs. In step-down mode, protection MOSFETs prevent reverse current. In step-up mode, the same MOSFETs regulate the output inrush current and use an adjustable timer circuit breaker to protect themselves.

Simplified Schematic

The LT8228 implements bidirectional input and output current limiting as well as independent current monitoring. Masterless, fault-tolerant current-sharing allows LT8228 chips to work in parallel and to be added or subtracted while maintaining current sharing accuracy. Internal and external fault diagnostics and reporting are available via separate pins (FAULT and REPORT). Each LT8228 regulates to the average output current, thus eliminating the need for a master controller. When an individual LT8228 is disabled or in a fault condition, it stops contributing to the average bus, making the current sharing scheme fault-tolerant. The LT8228 sits in a 38-lead TSSOP package.

The LT8228 controller provides a step-down output voltage when in buck mode or a step-up output voltage when in boost mode. The input and output voltage can be set as high as 100 V. In applications such as battery backup systems, the bidirectional feature allows the battery to be charged from either a higher or lower voltage supply. When the supply is unavailable, the battery boosts or bucks power back to the supply.

To optimize transient response, the LT8228 has two error amplifiers, one for boost mode, the other for buck mode with separate compensation pins. The controller operates in discontinuous conduction mode when reverse inductor current is detected for light load conditions.