L6566A View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566A' PDF : 52 Pages View PDF
Application information
L6566A
The operation described so far under different operating conditions for the converter is
illustrated in the timing diagrams of Figure 10.
If the FF option is selected, the operation is exactly equal to that of a standard current-mode
PWM controller. It works at a frequency fsw = fosc; both DCM and CCM transformer
operations are possible, depending on the operating conditions (input voltage and output
load) and on the design of the power stage. The MOSFET is turned on at the beginning of
each oscillator cycle and is turned off as the voltage on the current sense pin reaches an
internal reference set by the line feedforward block. The maximum duty cycle is limited at
70% minimum. The signal on the ZCD pin in this case is used only for detecting feedback
loop failures (see Section 5.11).
Figure 10. Operation of ZCD, triggering and oscillator blocks (QR option active)
ZCD
(pin 11)
100 mV
50 mV
Oscillator
ramp
ZCD
(pin 11)
100 mV
50 mV
Oscillator
ramp
ZCD
(pin 11)
100 mV
50 mV
Oscillator
ramp
ZCD
blanking
time
Arm/Trigger
armed
trigger
ZCD
blanking
time
Arm/Trigger
ZCD
blanking
time
Arm/Trigger
ON-enable
ON-enable
ON-enable
PWM latch
Set
PWM latch
Set
PWM latch
Set
PWM latch
Reset
PWM latch
Reset
PWM latch
Reset
GD
(pin 4)
GD
(pin 4)
GD
(pin 4)
a) full load
b) light load
c) start-up
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Doc ID 13794 Rev 4
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