The L6599AF is an improved revision of the previous L6599A. It is a double-ended controller specific to series-resonant half bridge topology. It provides 50% complementary duty cycle: the high-side switch and the low-side switch are driven ON/OFF 180° out-of-phase for exactly the same time. Output voltage regulation is obtained by modulating the operating frequency. A fixed deadtime inserted between the turn-off of one switch and the turn-on of the other guarantees soft-switching and enables high-frequency operation.
To drive the high-side switch with the bootstrap approach, the IC incorporates a high voltage floating structure able to withstand more than 600 V with a synchronous-driven high voltage DMOS that replaces the external fast-recovery bootstrap diode.
The IC enables the designer to set the operating frequency range of the converter by means of an externally programmable oscillator.
At startup, to prevent uncontrolled inrush current, the switching frequency starts from a programmable maximum value and progressively decays until it reaches the steady-state value determined by the control loop. This frequency shift is non-linear to minimize output voltage overshoots; its duration is programmable as well.
At light load the IC may enter a controlled burst mode operation that keeps the converter input consumption to a minimum.
IC functions include a not-latched active-low disable input with current hysteresis useful for power sequencing or for brownout protection, a current sense input for OCP with frequency shift and delayed shutdown with automatic restart. A higher level OCP latches off the IC if the first-level protection is not sufficient to control the primary current. Their combination offers complete protection against overload and short-circuits. An additional latched disable input (DIS) allows easy implementation of OTP and/or OVP.
An interface with the PFC controller is provided that enables the pre-regulator to be switched off during fault conditions, such as OCP shutdown and DIS high, or during burst mode operation.