L6591

Device description

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Device description

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 pre-

regulator 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.

Figure 2.

Typical system block diagram

 

L6561/2

or

L6563

PW M is turned off in case of PFC's

anomalous oper ation, for safety

PFC can be turned off at light

load to ease compliance with

energy saving r egulatio ns.

L6591

PFC PRE-REGULATOR

ZVS HALF-BRIDGE

L6561/2

or

L6563

PW M is turned off in case of PFC's

anomalous oper ation, for safety

PFC can be turned off at light

load to ease compliance with

energy saving r egulatio ns.

L6591

PFC PRE-REGULATOR

ZVS HALF-BRIDGE