This reference design is an open-loop LLC converter, which provides four 18 V and 2.5 V outputs, up to 2.4 W for onboard charger applications. The UCC25800-Q1 device is used here as the controller. The LLC topology allows the transformer to have significant leakage inductance, but a much smaller primary-secondary capacitance, which significantly reduces common-mode current injection through the bias transformer.
Parameter | Specifications |
---|---|
Input voltage range | 12 V |
Output voltage and current | 4 × (18 V and –2.5 V, 30 mA), 2.4 W maximum |
Nominal switching frequency | 400 kHz |
Isolation | Yes, 3000 VAC, 1 min |
Topology | Open-loop LLC |
The board dimensions are 55 mm (length) × 45 mm (width) × 25 mm (height).
Efficiency is shown in the following figure.