The L6562A is a current-mode PFC controller operating in Transition Mode (TM). Coming
with the same pin-out as its predecessors L6561 and L6562, it offers improved performance.
The highly linear multiplier includes a special circuit, able to reduce AC input current
distortion, that allows wide-range-mains operation with an extremely low THD, even over a
large load range.
The output voltage is controlled by means of a voltage-mode error amplifier and an accurate
(1% @T
The device features extremely low consumption (60µA max. before start-up and <5 mA
operating) and includes a disable function suitable for IC remote ON/OFF, which makes it
easier to comply with energy saving requirements (Blue Angel, EnergyStar, Energy2000,
etc.).
An effective two-step OVP enables to safely handle overvoltages either occurring at start-up
or resulting from load disconnection.
The totem-pole output stage, capable of 600 mA source and 800 mA sink current, is suitable
to drive high current MOSFETs or IGBTs. This, combined with the other features and the
possibility to operate with the proprietary Fixed-Off-Time control, makes the device an
excellent low-cost solution for EN61000-3-2 compliant SMPS in excess of 350W.
= 25°C) internal voltage reference.
J
3/26
Pin settingsL6562A
2 Pin settings
2.1 Pin connection
Figure 2.Pin connection (top view)
2.2 Pin description
Table 2. Pin description
Pin N°NameDescription
Inverting input of the error amplifier. The information on the output voltage of
1INV
2COMP
3MULT
the PFC pre-regulator is fed into this pin through a resistor divider. The pin
doubles as an ON/OFF control input.
Output of the error amplifier. A compensation network is placed between this
pin and INV to achieve stability of the voltage control loop and ensure high
power factor and low THD.
Main input to the multiplier. This pin is connected to the rectified mains
voltage via a resistor divider and provides the sinusoidal reference to the
current loop.
INV
COMP
MULT
CS
1
2
3
4
Vcc
8
GD
7
GND
6
ZCD
5
Input to the PWM comparator. The current flowing in the MOSFET is sensed
through a resistor, the resulting voltage is applied to this pin and compared
4CS
5ZCD
6GNDGround. Current return for both the signal part of the IC and the gate driver.
7GD
8Vcc
4/26
with an internal sinusoidal-shaped reference, generated by the multiplier, to
determine MOSFET’s turn-off. The pin is equipped with 200 ns leading-edge
blanking for improved noise immunity.
Boost inductor’s demagnetization sensing input for transition-mode
operation. A negative-going edge triggers MOSFET’s turn-on.
Gate driver output. The totem pole output stage is able to drive power
MOSFET’s and IGBT’s with a peak current of 600 mA source and 800 mA
sink. The high-level voltage of this pin is clamped at about 12V to avoid
excessive gate voltages in case the pin is supplied with a high Vcc.
Supply Voltage of both the signal part of the IC and the gate driver. The
supply voltage upper limit is extended to 22V min. to provide more headroom
for supply voltage changes.
Under steady-state conditions, the voltage control loop keeps the output voltage Vo of a
PFC pre-regulator close to its nominal value, set by the resistors R1 and R2 of the output
divider. Neglecting ripple components, the current through R1, I
I
. Considering that the non-inverting input of the error amplifier is internally referenced at
R2
2.5V, also the voltage at pin INV will be 2.5V, then:
Equation 1
V
I
R2IR1
2.5
------- -
R2
O
--------------------- -===
2.5–
R1
If the output voltage experiences an abrupt change ∆Vo > 0 due to a load drop, the voltage
at pin INV will be kept at 2.5V by the local feedback of the error amplifier, a network
connected between pins INV and COMP that introduces a long time constant to achieve
high PF (this is why ∆Vo can be large). As a result, the current through R2 will remain equal
to 2.5/R2 but that through R1 will become:
, equals that through R2,
R1
Equation 2
VO2.5–VO∆+
I'
--------------------------------------- -=
R1
R1
The difference current ∆IR1=I'R1-IR2=I'R1-IR1= ∆Vo/R1 will flow through the compensation
network and enter the error amplifier output (pin COMP). This current is monitored inside
the device and if it reaches about 24µA the output voltage of the multiplier is forced to
decrease, thus smoothly reducing the energy delivered to the output. As the current
exceeds 27µA, the OVP is triggered (Dynamic OVP): the gate-drive is forced low to switch
off the external power transistor and the IC put in an idle state. This condition is maintained
until the current falls below approximately 7µA, which re-enables the internal starter and
allows switching to restart. The output ∆Vo that is able to trigger the Dynamic OVP function
is then:
Equation 3
∆
VO = R1 · 20 · 10
- 6
An important advantage of this technique is that the OV level can be set independently of
the regulated output voltage: the latter depends on the ratio of R1 to R2, the former on the
individual value of R1. Another advantage is the precision: the tolerance of the detection
current is 13%, i.e. 13% tolerance on ∆Vo. Since ∆Vo << Vo, the tolerance on the absolute
value will be proportionally reduced.
R2 = 1.5 MΩ ·2.5/(400-2.5) = 9.43kΩ. The tolerance on the OVP level due to the L6562A will
be 40·0.13 = 5.3V, that is ± 1.2%.
13/26
Application informationL6562A
When the load of a PFC pre-regulator is very low, the output voltage tends to stay steadily
above the nominal value, which cannot be handled by the Dynamic OVP. If this occurs,
however, the error amplifier output will saturate low; hence, when this is detected the
external power transistor is switched off and the IC put in an idle state (Static OVP). Normal
operation is resumed as the error amplifier goes back into its linear region. As a result, the
device will work in burst-mode, with a repetition rate that can be very low.
When either OVP is activated the quiescent consumption of the IC is reduced to minimize
the discharge of the Vcc capacitor and increase the hold-up capability of the IC supply
system.
7.2 Disable function
The INV pin doubles its function as a not-latched IC disable: a voltage below 0.2V shuts
down the IC and reduces its consumption at a lower value. To restart the IC, the voltage on
the pin must exceed 0.45 V. The main usage of this function is a remote ON/OFF control
input that can be driven by a PWM controller for power management purposes. However it
also offers a certain degree of additional safety since it will cause the IC to shutdown in case
the lower resistor of the output divider is shorted to ground or if the upper resistor is missing
or fails open.
7.3 THD optimizer circuit
The device is equipped with a special circuit that reduces the conduction dead-angle
occurring to the AC input current near the zero-crossings of the line voltage (crossover
distortion). In this way the THD (Total Harmonic Distortion) of the current is considerably
reduced.
A major cause of this distortion is the inability of the system to transfer energy effectively
when the instantaneous line voltage is very low. This effect is magnified by the highfrequency filter capacitor placed after the bridge rectifier, which retains some residual
voltage that causes the diodes of the bridge rectifier to be reverse-biased and the input
current flow to temporarily stop.
14/26
L6562AApplication information
Figure 19. THD optimization: standard TM PFC controller (left side) and L6562A
(right side)
Input currentInput current
Rectified mains voltageRectified mains voltage
Imains
Input current
MOSFET's drain voltage
Vdrain
Imains
Input current
MOSFET's drain voltage
Vdrain
To overcome this issue the circuit embedded in the device forces the PFC pre-regulator to
process more energy near the line voltage zero-crossings as compared to that commanded
by the control loop. This will result in both minimizing the time interval where energy transfer
is lacking and fully discharging the high-frequency filter capacitor after the bridge. The effect
of the circuit is shown in figure 2, where the key waveforms of a standard TM PFC controller
are compared to those of the L6562A.
Essentially, the circuit artificially increases the ON-time of the power switch with a positive
offset added to the output of the multiplier in the proximity of the line voltage zero-crossings.
This offset is reduced as the instantaneous line voltage increases, so that it becomes
negligible as the line voltage moves toward the top of the sinusoid.
To maximally benefit from the THD optimizer circuit, the high-frequency filter capacitor after
the bridge rectifier should be minimized, compatibly with EMI filtering needs. A large
capacitance, in fact, introduces a conduction dead-angle of the AC input current in itself even with an ideal energy transfer by the PFC pre-regulator - thus making the action of the
optimizer circuit little effective.
15/26
Application informationL6562A
7.4 Operating with no auxiliary winding on the boost inductor
To generate the synchronization signal on the ZCD pin, the typical approach requires the
connection between the pin and an auxiliary winding of the boost inductor through a limiting
resistor. When the device is supplied by the cascaded DC-DC converter, it is necessary to
introduce a supplementary winding to the PFC choke just to operate the ZCD pin.
Another solution could be implemented by simply connecting the ZCD pin to the drain of the
power MOSFET through an R-C network as shown in figure 3: in this way the highfrequency edges experienced by the drain will be transferred to the ZCD pin, hence arming
and triggering the ZCD comparator.
Also in this case the resistance value must be properly chosen to limit the current
sourced/sunk by the ZCD pin. In typical applications with output voltages around 400V,
recommended values for these components are 22pF (or 33pF) for C
R
. With these values proper operation is guaranteed even with few volts difference
ZCD
between the regulated output voltage and the peak input voltage
Figure 20. ZCD pin synchronization without auxiliary winding
ZCD
C
ZCD
R
and 330k for
ZCD
ZCD
5
L6562A
16/26
L6562AApplication information
7.5 Comparison between the L6562A and the L6562
The L6562A is not a direct drop-in replacement of the L6562, even if both have the same
pin-out. One function (Disable) has been relocated.
Table 2 compares the two devices, i.e. those parameters that may result in different values
of the external components. The parameters that have the most significant impact on the
design, i.e. that definitely require external component changes when converting an L6562based design to the L6562A, are highlighted in bold.
Table 6. L6562A vs. L6562
Parameter L6562 L6562A
IC turn-on & turn-off thresholds (typ.) 12/9.5 V 12.5/10 V
Turn-off threshold spread (max.) ±0.8 V ±0.5 V
IC consumption before start-up (max.) 70 uA 60 uA
Multiplier gain (typ.) 0.6 0.38
Current sense reference clamp (typ.) 1.7 V 1.08 V
Current sense propagation delay (delay-to-output) (typ.) 200 ns 175 ns
Dynamic OVP triggering current (typ.) 40 uA 27 uA
ZCD arm/trigger/clamp thresholds (typ.) 2.1/1.4/0.7 V 1.4/0.7/0 V
Enable threshold (typ.)
Gate-driver internal drop (max.) 2.6 V 2.2 V
Leading-edge blanking on current sense No Yes
Reference voltage accuracy ( overall) 2.4%1.8%
1. Function located on pin 5 (ZCD)
2. Function located on pin 1 (INV)
0.3 V
(1)
0.45 V
(2)
The lower value (-36%) for the clamp level of the current sense reference voltage allows the
use of a lower sense resistor for the same peak current, with a proportional reduction of the
associated power dissipation. Essentially, the advantage is the reduction of the power
dissipated in a single point (hotspot), which is a considerable benefit in applications where
heat removal is critical, e.g. in adapters enclosed in a sealed plastic case. The lower value
for the Dynamic OVP triggering current allows the use of a higher resistance value (+48%)
for the upper resistor of the divider sensing the output voltage of the PFC stage (keeping the
same overvoltage level) with no significant increase of noise sensitivity. This reduction goes
in favor of standby consumption in applications required to comply with energy saving
regulations.
In order to meet environmental requirements, ST offers these devices in ECOPACK®
packages. These packages have a Lead-free second level interconnect . The category of
second level interconnect is marked on the package and on the inner box label, in
compliance with JEDEC Standard JESD97. The maximum ratings related to soldering
conditions are also marked on the inner box label. ECOPACK is an ST trademark.
ECOPACK specifications are available at: www.st.com
22/26
L6562APackage mechanical data
Table 7. DIP-8 mechanical data
mm Inch
Dim.
MinTypMaxMinTypMax
A 3.32 0.131
a1 0.51 0.020
B 1.15 1.65 0.045 0.065
b 0.356 0.55 0.014 0.022
b1 0.204 0.304 0.008 0.012
D 10.92 0.430
E 7.95 9.75 0.313 0.384
e 2.54 0.100
e3 7.62 0.300
e4 7.62 0.300
F 6.6 0.260
I 5.08 0.200
L 3.18 3.81 0.125 0.150
Z 1.52 0.060
Figure 31. Package dimensions
23/26
Package mechanical dataL6562A
Table 8. SO-8 mechanical data
Dim.
MinTypMaxMinTypMax
A 1.35 1.75 0.053 0.069
A1 0.10 0.25 0.004 0.010
A2 1.10 1.65 0.043 0.065
B 0.33 0.51 0.013 0.020
C 0.19 0.25 0.007 0.010
(1)
D
4.80 5.00 0.189 0.197
E 3.80 4.00 0.15 0.157
e 1.27 0.050
H 5.80 6.20 0.228 0.244
h 0.25 0.50 0.010 0.020
L 0.40 1.27 0.016 0.050
k 0° (min.), 8° (max.)
ddd 0.10 0.004
1. Dimensions D does not include mold flash, protru-sions or gate burrs. Mold flash, potrusions or gate burrs
shall not exceed 0.15mm (.006inch) in total (both side).
mm.inch
Figure 32. Package dimensions
24/26
L6562ARevision history
10 Revision history
Table 9. Revision history
DateRevisionChanges
03-Mar-20071First release
28-Jun-20072Updated electrical characteristics
07-Aug-20073Added Chapter 6: Typical electrical characteristic on page 9
25/26
L6562A
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