L6566ATR STMicroelectronics, L6566ATR Datasheet - Page 27

• Manufacturer Part Number: L6566ATR
• Description: IC CTRLR OVP UVLO 16SOIC
• Manufacturer: STMicroelectronics

Specifications of L6566ATR

• Output Isolation: Isolated
• Frequency Range: 93 ~ 107kHz
• Voltage - Input: 8 ~ 23 V
• Power (watts): 750mW
• Operating Temperature: -40°C ~ 150°C
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• For Use With: 497-8834 - BOARD DEMO FOR L6563/LL6566A497-6452 - BOARD EVAL FOR L6566B497-6451 - BOARD EVAL FOR L6566B497-6450 - BOARD EVAL FOR L6566B497-6449 - BOARD EVAL FOR L6566A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6296-2

L6566A
5.6
Figure 15. Externally controlled burst-mode operation by driving pin COMP: timing
PWM comparator, PWM latch and voltage feedforward blocks
The PWM comparator senses the voltage across the current sense resistor Rs and, by
comparing it to the programming signal delivered by the feedforward block, determines the
exact time when the external MOSFET is to be switched off. Its output resets the PWM
latch, previously set by the oscillator or the ZCD triggering block, which will assert the gate
driver output low. The use of PWM latch avoids spurious switching of the MOSFET that
might result from the noise generated (“double-pulse suppression”).
Cycle-by-cycle current limitation is realized with a second comparator (OCP comparator)
that senses the voltage across the current sense resistor Rs as well and compares this
voltage to a reference value V
the circuit schematic in
delivered by the feedforward block and sent to the PWM comparator exceeds V
the OCP comparator to reset first the PWM latch instead of the PWM comparator. The value
of Vcsx, thereby, determines the overcurrent setpoint along with the sense resistor Rs.
The power that QR flyback converters with a fixed overcurrent setpoint (like fixed-frequency
systems) are able to deliver changes with the input voltage considerably. Obviously, this is
not a problem if the flyback converter runs off a fixed voltage bus generated by the PFC pre-
regulator; however, with a tracking boost PFC (a “boost follower” PFC), the regulated output
voltage at maximum mains voltage can be even twice the value at minimum mains voltage.
In this case the issue is still there, although not as big as without PFC and wide-range
mains. With a 1:2 voltage change, the maximum transferable power at maximum line can be
50 % higher than at minimum line, as shown by the upper curve in the diagram of
The L6566A has the line feedforward function available to solve this issue.
diagram
Vcc_PFC
0.85 mA
Vcc_OK
(pin 6)
Vcc
Vout
COMP
(pin 9)
(pin 5)
(pin 4)
I
Vcc
charge
Vcc
Vcc
GD
restart
OFF
ON
Figure 17 on page 29
CSX
Standby is commanded here
. Its output is or-ed with that of the PWM comparator (see
). In this way, if the programming signal
Application information
t
t
t
t
t
t
t
CSX
Figure 16
, it will be
27/51
.