L6566B View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566B' PDF : 51 Pages View PDF
Application information
L6566B
If FF operation is selected:
1. FF mode from heavy to light load. The system operates exactly like a standard current
mode control, at a frequency fsw determined by the externally programmable oscillator:
both DCM and CCM transformer operation are possible, depending on whether the
power that it processes is greater or less than:
Equation 1
Pin T
=
⎜⎜⎝⎛
Vin VR
Vin + VR
⎟⎟⎠⎞ 2
2 fsw Lp
where Vin is the input voltage to the converter, VR the reflected voltage (i.e. the
regulated output voltage times the primary-to-secondary turn ratio) and Lp the
inductance of the primary winding. PinT is the power level that marks the transition from
continuous to discontinuous operation mode of the transformer.
2. Burst-mode with no or very light load. This kind of operation is activated in the same
way and results in the same behavior as previously described for QR operation.
The L6566B is specifically designed for applications with no PFC front-end; pin 6 (FMOD)
features an auxiliary oscillator that can modulate the switching frequency (when FF
operation is selected) in order to mitigate EMI emissions by a spread-spectrum action.
5.1
High-voltage start-up generator
Figure 5 shows the internal schematic of the high-voltage start-up generator (HV generator).
It is made up of a high-voltage N-channel FET, whose gate is biased by a 15 MΩ resistor,
with a temperature-compensated current generator connected to its source.
Figure 5.
High-voltage start-up generator: internal schematic
HV
L6566B
15 M
1
Vcc_OK
HV_EN
IHV
CONTROL
3
GND
5 Vcc
I charge
18/51
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