STEVAL-L6983IV1 Synchronous Iso-Buck Converter Evaluation Board

STMicroelectronics' STEVAL-L6983IV1 is an evaluation board based on the ST L6983I 38 V, 10 W synchronous iso-buck converter designed for isolated applications. The primary output voltage can be accurately adjusted, whereas the isolated secondary output is derived using a given transformer ratio. No optocoupler is required. The primary sink capability up to -4.5 A (even during soft-start) allows proper energy transfer to the secondary side and enables a tracked soft-start of the secondary output. The control loop is based on a peak current mode architecture, and the device operates in forced PWM. The 390 ns blanking time filters oscillations generated by the transformer leakage inductance, making the solution more robust.

The compact QFN-16 3 mm x 3 mm package and the internal compensation of the L6983I help minimize design complexity and size. The switching frequency can be programmed in the 200 kHz to 1 MHz range with an optional spread spectrum for improved EMC. The EN pin provides enable/disable functionality. The typical shutdown current is 2 µA when disabled. As soon as the EN pin is pulled up, the device is enabled and the internal 1.3 ms soft-start takes place.

The L6983I features a power good open collector that monitors the FB voltage. Pulse-by-pulse current sensing on both power elements implements effective constant current protection, and thermal shutdown prevents thermal runaway. Due to the primary reverse current limit, the secondary output is protected against short-circuit events. The evaluation board generates an isolated unregulated voltage and allows the use of postregulation to generate a dual voltage (layout available on the bottom of the PCB, components not mounted).