DC-DC Converters Optimized for Battery Management Systems

Mornsun has introduced 50Vdc and 60Vdc dc-dc converter, the B05xxLD-1WR2 and B05xxLS-1WR2 series, respectively, designed specifically for battery management systems (BMS). These dc-dc converters are optimized for BMS employing the LTC680X chip from Linear Technology to monitor each lithium battery block. The series meets the requirements of EMI CISPR25 CLASS 3 standard and electrostatic discharge of ISO 10605±8KV and have high reliability. The operating temperature range is -40 to +85 degrees C and they have 1500Vdc input-to-output isolation.

Linear Technology’s LT8584 is a monolithic flyback dc-dc converter designed to actively balance high voltage stacks of batteries. These battery stacks are commonly found in electric and hybrid vehicles as well as failsafe power supplies and energy storage systems. Because these batteries are stacked in series, the lowest capacity battery will limit the entire battery stack’s run-time. Ideally, the batteries would be perfectly matched, but this is often not the case and generally gets worse as the batteries age.

Passive energy balancing offers no improved run-time as it dissipates the added energy of the higher capacity batteries to match the lowest one. Conversely, the LT8584 offers high efficiency active balancing, which redistributes the charge from the stronger cells (higher voltage) to charge the weaker cells during discharge. This enables the weaker cells to continue to supply the load, extracting 96% of the entire stack capacity where passive balancing usually extracts approximately 80%.

The LT8584 includes an integrated 6A/50V power switch, enabling an average discharge current of 2.5A while offering a simple and compact application circuit. Its isolated balancing design can return charge to the top of the battery stack or to any combination of cells in the stack or even to a 12V battery used as an alternator replacement. The LT8584 runs off of the cell that it is discharging, removing the need for complicated biasing schemes. It integrates seamlessly via the enable pin with the LTC680x family of battery stack voltage monitoring ICs without any additional software.

The LT8584 also provides system telemetry, including current, resistance and temperature monitoring when used with the LTC680x family of parts. When the LT8584 is disabled, it draws less than 20nA of quiescent current from the battery. For applications that require higher balancing current, multiple LT8584s can be paralleled. It is packaged in a 16-lead TSSOP and is both FMEA and ISO 26262 compliant.