The L6591 is a double-ended PWM controller specific for the soft-switched half-bridge
topology. It provides complementary PWM control, where the high-side switch is driven ON
for a duty cycle D and the low-side switch for a duty cycle 1-D, with D 50 %. An externally
programmable dead-time inserted between the turn-off of one switch and the turn-on of the
other one 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 of the converter by means of an
externally programmable oscillator: the maximum duty cycle is digitally clipped at 50 % by a
T-flip-flop, so that the operating frequency will be half that of the oscillator.
At very light load the IC enters a controlled burst-mode operation that, along with the built-in
non-dissipative high-voltage start-up circuit and the low quiescent current, helps keep low
the consumption from the mains and be compliant with energy saving recommendations.
To allow compliance with these standards in two-stage power-factor-corrected systems as
well, an interface with the PFC controller is provided that enables to switch off the preregulator
between one burst and the following one.
An innovative adaptive UVLO helps minimize the issues related to the fluctuations of the
self-supply voltage with the output load, due to transformer's parasitic.
IC's protection functions include: not-latched input undervoltage (brownout), a first-level
OCP with delayed shutdown able to protect the system during overload and short circuit
conditions (either auto-restart or latch mode can be selected) and a second-level OCP that
latches off the IC when the transformer saturates or one of the secondary diodes fails short.
Finally, a latched disable function allows easy implementation of OTP or OVP.
Programmable soft-start and digital leading-edge blanking on current sense input pin
complete the equipment of the IC.