L6566B STMicroelectronics, L6566B Datasheet - Page 29

• Manufacturer Part Number: L6566B
• Description: IC CTRLR OVP OTP UVLO HV 16SOIC
• Manufacturer: STMicroelectronics

Specifications of L6566B

• Output Isolation: Isolated
• Frequency Range: 10 ~ 300kHz
• Voltage - Input: 8 ~ 23 V
• Power (watts): 750mW
• Operating Temperature: -40°C ~ 150°C
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• Output Current: 800 mA
• Output Power: 750 mW
• Input Voltage: 8 V to 23 V
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: SMD/SMT
• Duty Cycle (max): 75 %
• Selectable Multi-mode Operation: fixed frequency or quasi-resonant
• For Use With: 497-6452 - 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

L6566B
Figure 17. Left: overcurrent setpoint vs VFF voltage; right: line feedforward function block
V
1.2
0.8
0.6
0.4
0.2
csx
1
0
0
[V]
0.5
Experience shows that this value is typically lower than the real one. Once the maximum
peak primary current, I
the value of Rs can be determined from (5):
Equation 7
The converter is then tested on the bench to find the output power level Pout
regulation is lost (because overcurrent is being tripped) both at Vin = Vin
Vin = Vin
If Pout
increasing; if Pout
needs decreasing. This will go on until the difference between the two values is acceptably
low. Once found the true k
from the target; to correct this, the sense resistor Rs needs adjusting and the above tuning
process will be repeated with the new Rs value. Typically a satisfactory setting is achieved in
no more than a couple of iterations.
In applications where this function is not wanted, e.g. because of a narrow input voltage
range, the VFF pin can be simply grounded, directly or through a resistor, depending on
whether one wants the OVP function to be auto-restart or latched mode (see “
OVP block on page 35
1V. If a lower setpoint is desired to reduce the power dissipation on Rs, the pin can be also
biased at a fixed voltage using a divider from VREF (pin 10).
If the FF option is selected the line feedforward function can be still used to compensate for
the total propagation delay Td of the current sense chain (internal propagation delay td
plus the turn-off delay of the external MOSFET), which in standard current mode PWM
controllers is done by adding an offset on the current sense pin proportional to the input
voltage. In that case the divider ratio k, which will be much smaller as compared to that used
with the QR option selected, can be calculated with the following equation:
1
lim
1.5
V
max
@ Vin
VFF
[V]
.
V
COMP
2
= Upper clamp
max
lim
2.5
> Pout
@ Vin
”). The overcurrent setpoint will be then fixed at the maximum value of
PKpmax
3
lim
opt
max
@ Vin
in this way, it is possible that Pout
, occurring at minimum input voltage Vinmin has been found,
3.5
< Pout
min
Rs
lim
the system is still undercompensated and k needs
=
COMP
Rectif ied Line Voltage
@ Vin
1
−
R1
R2
9
I
L6566B
k
PKp
opt
3
min
15
max
V
VFF
the system is overcompensated and k
in
FORWARD
VOLTAGE
min
OVP settings
Optional for
FEED
Vcsx
1.5 V
CS
7
+
+
+
Hiccup
-
-
-
PWM
OCP
lim
turns out slightly different
Rs
Application information
Clock/ZCD
min
R
S
Q
and
lim
DISABLE
Section 5.11:
where
DRIVER
4
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