L6566ATR(2007) データシートの表示（PDF） - STMicroelectronics
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L6566ATR Datasheet PDF : 51 Pages
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Description
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Description
L6566A
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 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 IC works like a standard current-mode controller with a
maximum duty cycle limited at 70% min.
QR operation, when selected, occurs 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
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 start-up circuit and a
reduced quiescent current, helps keep low the consumption from the mains and meet
energy saving recommendations.
To allow meeting them in two-stage power-factor-corrected systems as well, the L6566A
provides an interface with the PFC controller that enables to turn off the pre-regulator at light
load.
An innovative adaptive UVLO helps minimize the issues related to the fluctuations of the
self-supply voltage due to transformer's parasitics.
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.
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