The L6566A is an extremely versatile current-mode primary controller IC specifically designed for high-performance offline flyback converters operated from front-end power factor correction (PFC) stages in applications in compliance with EN61000-3-2 or JEITA-MITI regulations.
Both fixed-frequency (FF) and quasi-resonant (QR) operation are supported. The user can choose either of the two depending on application needs.
The device features an externally programmable oscillator; it defines the converter's switching frequency in FF mode and the maximum allowed switching frequency in QR mode.
When FF operation is selected, the IC works like a standard current-mode controller with a maximum duty cycle limited to 70% (min.).
QR operation, when selected, occurs and is achieved through a transformer demagnetization sensing input that triggers MOSFET turn-on. Under some conditions, ZVS (zero-voltage switching) can be achieved. The converter's power capability rise with the input voltage is compensated by line voltage feedforward. At medium and light load, as the QR operating frequency equals the oscillator frequency, a function (valley skipping) is activated to prevent further frequency rise and keep the operation as close to ZVS as possible.
With either FF or QR operation, at very light load the IC enters a controlled burst-mode operation that, along with the built-in non-dissipative high-voltage startup circuit and a reduced quiescent current, helps keep the consumption from the mains low and meet energy saving recommendations.
To allow the meeting of energy saving recommendations in two-stage power-factor-corrected systems as well, the L6566A provides an interface with the PFC controller that enables the re-regulator to be turned off at light load.
An innovative adaptive UVLO helps minimize the issues related to fluctuations in the self-supply voltage due to transformer parasites.
The protection functions included in this device are: not-latched input undervoltage (brownout), output OVP (auto-restart or latch-mode selectable), a first-level OCP with delayed shutdown to protect the system during overload or short-circuit conditions (auto-restart or latch-mode selectable), and a second-level OCP which is invoked when the transformer saturates or the secondary diode fails short. A latched disable input allows easy implementation of OTP with an external NTC, while an internal thermal shutdown prevents IC overheating.
Programmable soft-start, leading-edge blanking on the current sense input for greater noise immunity, slope compensation (in FF mode only), and a shutdown function for externally controlled burst-mode operation or remote ON/OFF control are all features of this device.