L6566B datasheet(6/51 Pages) STMICROELECTRONICS

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Description

L6566B

6/51

Description

The L6566B is an extremely versatile current-mode primary controller ICs, specifically

designed for high-performance offline flyback converters. It is also suited for single-stage

single-switch input-current-shaping converters (single-stage PFC) for applications supposed

to comply with EN61000-3-2 or JEITA-MITI regulations.

Both fixed-frequency (FF) and quasi-resonant (QR) operation are supported. The user can

pick either of the two depending on application needs. The device features an externally

programmable oscillator: it defines converter’s switching frequency in FF mode and the

maximum allowed switching frequency in QR mode.

When FF operation is selected, the ICs work like a standard current-mode controller with a

maximum duty cycle limited at 70 % min. The oscillator frequency can be modulated to

mitigate EMI emissions.

QR operation, when selected, occurs at heavy load and is achieved through a transformer

demagnetization sensing input that triggers MOSFET’s turn-on. Under some conditions,

ZVS (zero-voltage switching) can be achieved. Converter’s power capability rise with the

mains 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 ICs enter 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 meet energy saving

recommendations.

An innovative adaptive UVLO helps minimize the issues related to the fluctuations of the

self-supply voltage due to transformer’s 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 that 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 complete the equipment of this

device.

L6566B Arkusz danych(PDF) 6 Page - STMicroelectronics