L6699DTR

Features

■ Symmetrical duty cycle, variable frequency

control of resonant half bridge

■ Self-adjusting adaptive deadtime

■ High-accuracy oscillator

■ 2-level OCP: frequency-shift and immediate

shutdown

■ Interface with PFC controller

■ Anti-capacitive-mode protection

■ Burst-mode operation at light load

■ Input for brownout protection or power-on/off

sequencing

■ “Safe-start” procedure prevents hard switching

at startup

■ 600 V rail compatible high-side gate driver with

integrated bootstrap diode and high dv/dt

immunity

■ -300/800 mA high-side and low-side gate

drivers with UVLO pull-down

■ SO16N package

Applications

■ SMPS for LCD TVs, desktop and AIO PCs,

servers, Telecom power

■ AC-DC adapter, open frame SMPS

Description

The L6699 is a double-ended controller specific to series-resonant half bridge topology. Both LLC and LCC configurations are supported. It provides symmetrical complementary duty cycle: the high-side switch and the low-side switch are driven ON/OFF 180° out-ofphase for exactly the same time. Output voltage regulation is obtained by modulating the operating frequency. The deadtime inserted between the turn-off of one switch and the turnon of the other one is automatically adjusted to best fit the transition times of the half bridge midpoint. 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 user to set the operating frequency range of the converter by means of a high-accuracy externally programmable oscillator.

At startup, in addition to the traditional frequency-shift soft-start (the switching frequency starts from a preset maximum value and then decays as far as the steady-state value determined by the control loop), a proprietary circuit controls the half bridge to prevent hardswitching from occurring in the initial cycles because of the unbalance in the V·s applied to the transformer.

At light load the IC can be forced to enter a controlled burst-mode operation that keeps the converter input consumption as low as possible.

IC protection functions include a current sense input for OCP with frequency shift and delayed shutdown with automatic restart. Fast shutdown with automatic restart occurs if this

first-level protection cannot control the primary current. Additionally, the IC prevents the converter from working in or too close to the capacitive mode, to guarantee soft-switching. A latched disable input (DIS) can be used to implement OTP and/or OVP. The combination of these protection features offers the highest degree of safety.

Other functions include a not-latched active-low disable input with current hysteresis, useful for power sequencing or for brownout protection, and an interface with the PFC controller that enables the switching-off of the pre-regulator during fault conditions or during burstmode operation. 

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