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The L6983I is a device specifically designed for isolated buck topology. The primary output voltage can be accurately adjusted, whereas the isolated secondary output is derived by using a given transformer ratio. No optocoupler is required. The primary sink capability up to -4.5 A (even during soft-start) allows a proper energy transfer to the secondary side as well as enabling 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 QFN16 3x3 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 - 1 MHz range with 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 Power Good open collector that monitors the FB voltage. Pulse by pulse current sensing on both power elements implements an effective constant current protection and thermal shutdown prevents thermal run-away.