AN4026 Datasheet, PDF (6/40 Pages) STMicroelectronics – using the L6563H and L6699

Main characteristics and circuit description
1
Main characteristics and circuit description
AN4026
The main features of the SMPS are listed here below:
● Universal input mains range: from 90 to 264 Vac - frequency from 45 to 65 Hz
● Output voltage: 19 V at 4.75 A continuous operation
● Mains harmonics: meets EN61000-3-2 Class-D and JEITA-MITI Class-D
● No load mains consumption: according to ENERGY STAR 2.0 for external power
supplies
● Average efficiency: according to ENERGY STAR 2.0 for external power supplies
● Light load efficiency: according to ErP Lot 6 Tier2 requirements
● EMI: within EN55022-Class-B limits
● Safety: meets EN60950
● Dimensions: 65 x 151 mm, 25 mm components maximum height
● PCB: double side, 70 µm, FR-4, mixed PTH/SMT.
The circuit is made up of two stages: a front-end PFC using the L6563H and an LLC
resonant converter featuring the L6699.
The PFC stage works as pre-regulator and powers the resonant stage with a constant
voltage of 400 V. The downstream converter operates only if the PFC is working and
regulating its output voltage. In this way, the resonant stage can be optimized for a narrow
input voltage range improving the efficiency of the primary side power components.
1.1
Startup sequence
As previously indicated, the PFC acts as master and the resonant stage can operate only if
the PFC output is delivering its rated output voltage. Therefore the circuit is designed so that
at startup the PFC starts first, the downstream converter then turns on by means of the
LINE pin (#7). At the beginning, the L6563H is supplied by the integrated high-voltage
startup circuit; once the PFC starts switching, a charging pump connected to the PFC
inductor supplies both PFC and resonant controllers. Once both stages are working, the
controllers are supplied also by the auxiliary winding of the resonant transformer, assuring
correct supply voltage even during standby operation.
After reaching the turn-on threshold on the VCC pin the L6563H integrated HV startup
circuit is turned off and it is therefore not dissipative during normal operation, significantly
contributing to the reduction of input power consumption once the power supply operates at
light load, and meeting the standby worldwide efficiency standards that are currently
required.
1.2
Brownout protection
Brownout protection prevents the circuit from working with abnormal mains levels. It is easily
achieved using the pin RUN (#12) of the L6563H: this pin is connected through a resistor
divider to the pin VFF (#5) which provides a DC voltage the same as the peak of the MULT
pin (#3) signal which is a partition of the rectified mains input voltage. An L6563H internal
comparator allows IC operations only if the mains level is correct, within the nominal limits,
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Doc ID 022603 Rev 1