LNK623-626
™
LinkSwitch-CV
Family
Energy-Efficient, Off-line Switcher with Accurate
Primary-side Constant-Voltage (CV) Control
Product Highlights
Dramatically Simplifies CV Converters
•
Eliminates optocoupler and all secondary CV control circuitry
•
Eliminates bias winding supply – IC is self biasing
Advanced Performance Features
•
Compensates for external component temperature variations
•
Very tight IC parameter tolerances using proprietary trimming
technology
•
Continuous and/or discontinuous mode operation for design
flexibility
•
Frequency jittering greatly reduces EMI filter cost
•
Even tighter output tolerances achievable with external resistor
selection/trimming
Advanced Protection/Safety Features
•
Auto-restart protection reduces delivered power by >95% for
output short-circuit and all control loop faults (open and shorted
components)
•
Hysteretic thermal shutdown – automatic recovery reduces
power supply returns from the field
•
Meets HV creepage requirements between Drain and all other
pins, both on the PCB and at the package
EcoSmart
™
– Energy Efficient
•
No-load consumption <200 mW at 230 VAC and down to
below 70 mW with optional external bias
•
Easily meets all global energy efficiency regulations with no
added components
•
ON/OFF control provides constant efficiency down to very light
loads – ideal for mandatory EISA and ENERGY STAR 2.0
regulations
•
No primary or secondary current sense resistors – maximizes
efficiency
Green Package
•
Halogen free and RoHS compliant package
Applications
•
DVD/STB
•
Adapters
•
Standby and auxiliary supplies
•
Home appliances, white goods and consumer electronics
•
Industrial controls
*
Wide Range
HV DC Input
LinkSwitch-CV
D
FB
BP
S
(a) Typical Application Schematic
V
O
±5%
PI-5195-080808
Au
to
st
-Re
art
PI-5196-080408
I
O
(b) Output Characteristic
Figure 1.
Typical Application Schematic (a) and Output Characteristic Envelope (b).
*Optional with LNK623-624PG/DG. (see Key Application Considerations section for
clamp and other external circuit design considerations).
Output Power Table
230 VAC ±15%
Product
3
85-265 VAC
Adapter
1
5.0 W
5.5 W
6.5 W
8.5 W
Peak or
Open
Frame
2
6W
6.5 W
8W
10 W
Adapter
1
6.5 W
7W
8W
10.5 W
Peak or
Open
Frame
2
9W
11 W
13.5 W
17 W
LNK623PG/DG
LNK624PG/DG
LNK625PG/DG
LNK626PG/DG
Description
The LinkSwitch-CV dramatically simplifies low power, constant
voltage (CV) converter design through a revolutionary control
technique which eliminates the need for both an optocoupler and
secondary CV control circuitry while providing very tight output
voltage regulation. The combination of proprietary IC trimming
and E-Shield™ transformer construction techniques enables
Clampless™ designs with the LinkSwitch-CV LNK623/4.
www.powerint.com
Table 1. Output Power Table. Based on 5 V Output.
Notes:
1. Minimum continuous power in a typical non-ventilated enclosed adapter
measured at +50 °C ambient.
2. Maximum practical continuous power in an open frame design with adequate
heat sinking, measured at 50 °C ambient (see Key Application Considerations
section for more information).
3. Packages: P: DIP-8C, D: SO-8C.
LinkSwitch-CV provides excellent cross-regulation for multiple-
output flyback applications such as DVDs and STBs. A 700 V
power MOSFET and ON/OFF control state machine, self-biasing,
frequency jittering, cycle-by-cycle current limit, and hysteretic
thermal shutdown circuitry are all incorporated onto one IC.
March 2014
This Product is Covered by Patents and/or Pending Patent Applications.
LNK623-626
BYPASS
(BP)
+
-
REGULATOR
+
-
DRAIN
(D)
FEEDBACK
(FB)
V
TH
D
FB
OUT
STATE
MACHINE
I
LIM
Reset
V
ILIMIT
Drive
6V
5V
t
SAMPLE-OUT
DC
MAX
6.5 V
FB
FAULT
Auto-Restart
Open-Loop
THERMAL
SHUTDOWN
t
SAMPLE-OUT
OSCILLATOR
I
LIM
+
-
DC
MAX
SAMPLE
DELAY
SOURCE
(S)
V
ILIMIT
LEADING
EDGE
BLANKING
SOURCE
(S)
Current Limit
Comparator
PI-5197-110408
Figure 2
Functional Block Diagram.
Pin Functional Description
DRAIN (D) Pin:
This pin is the power MOSFET drain connection. It provides
internal operating current for both start-up and steady-state
operation.
BYPASS (BP) Pin:
This pin is the connection point for an external bypass capacitor
for the internally generated 6 V supply.
FEEDBACK (FB) Pin:
During normal operation, switching of the power MOSFET is
controlled by this pin. This pin senses the AC voltage on the
bias winding. This control input regulates the output voltage
based on the flyback voltage of the bias winding.
SOURCE (S) Pin:
This pin is internally connected to the output MOSFET source
for high-voltage power and control circuit common returns.
P Package (DIP-8C)
FB
BP
D Package (SO-8C)
1
2
8
7
6
S
S
S
S
FB
BP
D
1
2
8
7
6
S
S
S
S
D
4
3a
5
4
5
3b
PI-5198-071608
Figure 3.
Pin Configuration.
2
Rev. F 03/14
www.powerint.com
LNK623-626
LinkSwitch-CV Functional Description
The LinkSwitch-CV combines a high-voltage power MOSFET
switch with a power supply controller in one device. Similar to
the LinkSwitch-LP and TinySwitch-III it uses ON/OFF control to
regulate the output voltage. The LinkSwitch-CV controller
consists of an oscillator, feedback (sense and logic) circuit, 6 V
regulator, over-temperature protection, frequency jittering,
current limit circuit, leading-edge blanking, and ON/OFF state
machine for CV control.
Constant Voltage (CV) Operation
The controller regulates the FEEDBACK pin voltage to remain
at V
FBth
using an ON/OFF state-machine. The FEEDBACK pin
voltage is sampled 2.5
ms
after the turn-off of the high-voltage
switch. At light loads the current limit is also reduced to
decrease the transformer flux density.
Auto-Restart and Open-Loop Protection
In the event of a fault condition such as an output short or an
open loop condition the LinkSwitch-CV enters into an
appropriate protection mode as described below.
In the event the FEEDBACK pin voltage during the Flyback
period falls below V
FBth
-0.3 V before the FEEDBACK pin
sampling delay (~2.5
ms)
for a duration in excess of 200 ms
(auto-restart on-time (t
AR-ON
) the converter enters into auto-
restart, wherein the power MOSFET is disabled for 2.5 seconds
(~8% auto-restart duty cycle). The auto-restart alternately
enables and disables the switching of the power MOSFET until
the fault condition is removed.
In addition to the conditions for auto-restart described above, if
the sensed FEEDBACK pin current during the Forward period of
the conduction cycle (switch “on” time) falls below 120
mA,
the
converter annunciates this as an open-loop condition (top
resistor in potential divider is open or missing) and reduces the
auto-restart time from 200 ms to approximately 6 clock cycles
(90
ms),
whilst keeping the disable period of 2.5 seconds. This
effectively reduces the auto-restart duty cycle to less than 0.01%.
Over-Temperature Protection
The thermal shutdown circuitry senses the die temperature. The
threshold is set at 142 °C typical with a 60 °C hysteresis. When
the die temperature rises above this threshold (142 °C) the
power MOSFET is disabled and remains disabled until the die
temperature falls by 60 °C, at which point the MOSFET is
re-enabled.
Current Limit
The current limit circuit senses the current in the power
MOSFET. When this current exceeds the internal threshold
(I
LIMIT
), the power MOSFET is turned off for the remainder of that
cycle. The leading edge blanking circuit inhibits the current limit
comparator for a short time (t
LEB
) after the power MOSFET is
turned on. This leading edge blanking time has been set so that
current spikes caused by capacitance and rectifier reverse
recovery time will not cause premature termination of the
MOSFET conduction.
6.0 V Regulator
The 6 V regulator charges the bypass capacitor connected to the
BYPASS pin to 6 V by drawing a current from the voltage on the
DRAIN, whenever the MOSFET is off. The BYPASS pin is the
internal supply voltage node. When the MOSFET is on, the
device runs off of the energy stored in the bypass capacitor.
Extremely low power consumption of the internal circuitry allows
the LinkSwitch-CV to operate continuously from the current
drawn from the DRAIN pin. A bypass capacitor value of 1
mF
is
sufficient for both high frequency decoupling and energy storage.
3
www.powerint.com
Rev. F 03/14
LNK623-626
Applications Example
L1
3.5 × 7.6 mm
Ferrite Bead
1
R1
5.1 kΩ
1/8 W
VR1
1N5272B
T1
EEL19
6
D8
UF4003
C9
47
µF
25 V
D7 SB540
R8
24 kΩ
1/8 W
12 V, 0.1 A
D1
FR106
D2
FR106
C3
820 pF
1 kV
3
7
L3
10
µH
C10
470
µF
10 V
R9
39 kΩ
1/8 W
5 V, 1.7 A
R7
510
Ω
1/8 W
RTN
11
8,9,10
R10
47
Ω
C13
270 pF
C8
1000
µF
10 V
C11
47
µF
50 V
L
85 - 265
VAC
N
F1
3.15 A
C1
22
µF
400 V
RT1
10
Ω
RV1
275 V
C2
22
µF
400 V
R2
390
Ω
D5
1N4007
12
5
D9
UF4003
D6
1N4148
-22 V, 15 mA
4
2
D3
1N4007
D4
1N4007
D
LinkSwitch-CV
U1
LNK626PG
FB
BP
R3
6.34 kΩ
1%
S
R4
6.2 kΩ
C4
1
µF
50 V
L2
680 uH
R5
47 kΩ
1/8 W
R6
4.02 kΩ
C5
1%
680 pF
50 V
C6
10
µF
50 V
PI-5205-102208
Figure 4.
7 W (10 W peak) Multiple Output Flyback Converter for DVD Applications with Primary Sensed Feedback.
Circuit Description
This circuit is configured as a three output, primary-side
regulated flyback power supply utilizing the LNK626PG. It can
deliver 7 W continuously and 10 W peak (thermally limited) from
an universal input voltage range (85 – 265 VAC). Efficiency is
>67% at 115 VAC/230 VAC and no-load input power is
<140 mW at 230 VAC.
Input Filter
AC input power is rectified by diodes D1 through D4. The
rectified DC is filtered by the bulk storage capacitors C1 and
C2. Inductor L1, L2, C1 and C2 form a pi (π) filter, which
attenuates conducted differential-mode EMI noise. This
configuration along with Power Integrations transformer
E-shield
™
technology allow this design to meet EMI standard
EN55022 class B with good margin without requiring a
Y capacitor. Fuse F1 provides protection against catastrophic
failure. Negative temperature coefficient thermistor RT1 limits
the inrush current when AC is first applied to below the
maximum rating of diodes D1 through D4. Metal oxide varistor
RV1 clamps the AC input during differential line transients,
protecting the input components and maintaining the peak
drain voltage of U1 below its 700 V BV
DSS
rating. For differential
surge levels at or below 2 kV this component may be omitted.
LNK626 Primary
The LNK626PG device (U1) incorporates the power switching
device, oscillator, CV control engine, startup, and protection
functions. The integrated 700 V MOSFET provides a large drain
voltage margin in universal input AC applications, increasing
reliability and also reducing the output diode voltage stress by
allowing a greater transformer turns ratio. The device can be
completely self-powered from the BYPASS pin and decoupling
capacitor C4. In this design a bias circuit (D6, C6 and R4) was
added to reduce no load input power below 140 mW.
The rectified and filtered input voltage is applied to one side of
the primary winding of T1. The other side of the transformer’s
primary winding is driven by the integrated MOSFET in U1. The
leakage inductance drain voltage spike is limited by the clamp
circuit D5, R1, R2, C3 and VR1. The Zener bleed clamp
arrangement was selected for lowest no-load input power but in
applications where higher no-load input power is acceptable
VR1 may be omitted and the value of R1 increased to form a
standard RCD clamp.
Output Rectification
The secondaries of the transformer are rectified by D7, D8 and
D9. A Schottky barrier type was used for the main 5 V output
for higher efficiency. The +12 V and -22 V outputs use an
ultrafast rectifier diode. The main output is post filtered by L3
and C10 to remove switching frequency ripple. Resistors R7,
R8 and R9 provide a preload to maintain the output voltages
within their respective limits when unloaded. To reduce high
frequency ringing and associated radiated EMI an RC snubber
formed by R10 and C13 was added across D7.
4
Rev. F 03/14
www.powerint.com
LNK623-626
Output Regulation
The LNK626 regulates the output using ON/OFF control, enabling
or disabling switching cycles based on the sampled voltage on
the FEEDBACK pin. The output voltage is sensed using a
primary referenced winding on transformer T1 eliminating the
need for an optocoupler and a secondary sense circuit. The
resistor divider formed by R3 and R6 feeds the winding voltage
into U1. Standard 1% resistor values were used to center the
nominal output voltages. Resistor R5 and C5 reduce pulse
grouping by creating an offset voltage that is proportional to the
number of consecutive enabled switching cycles.
voltages together with analog signals makes it especially
important to follow good PCB design practice to ensure stable
and trouble free operation of the power supply.
When designing a board for the LinkSwitch-CV based power
supply, it is important to follow the following guidelines:
Single Point Grounding
Use a single point (Kelvin) connection at the negative terminal of
the input filter capacitor for the LinkSwitch-CV SOURCE pin and
bias winding return. This improves surge capabilities by
returning surge currents from the bias winding directly to the
input filter capacitor.
Bypass Capacitor
The BYPASS pin capacitor should be located as close as
possible to the SOURCE and BYPASS pins.
Feedback Resistors
Place the feedback resistors directly at the FEEDBACK pin of
the LinkSwitch-CV device. This minimizes noise coupling.
Thermal Considerations
The copper area connected to the SOURCE pins provide the
LinkSwitch-CV heat sink. A rule of thumb estimate is that the
LinkSwitch-CV will dissipate 10% of the output power. Provide
enough copper area to keep the SOURCE pin temperature
below 110° C to provide margin for part to part R
DS(ON)
variation.
Secondary Loop Area
To minimize leakage inductance and EMI, the area of the loop
connecting the secondary winding, the output diode and the
output filter capacitor should be minimized. In addition,
sufficient copper area should be provided at the anode and
cathode terminal of the diode for heat sinking. A larger area is
preferred at the quiet cathode terminal. A large anode area can
increase high frequency radiated EMI.
Electrostatic Discharge Spark Gap
In chargers and adapters ESD discharges may be applied to
the output of the supply. In these applications the addition of a
spark gap is recommended. A trace is placed along the isolation
barrier to form one electrode of a spark gap. The other electrode,
on the secondary side, is formed by the output return node.
The arrangement directs ESD energy from the secondary to the
primary side AC input. A 10 mil gap is placed near the AC
input. The gap decouples any noise picked up on the spark
gap trace to the AC input. The trace from the AC input to the
spark gap electrode should be spaced away from other traces
to prevent unwanted arcing occurring and possible circuit damage.
Key Application Considerations
Output Power Table
The data sheet maximum output power table (Table 1)
represents the maximum practical continuous output power
level that can be obtained in a Flyback converter under the
following assumed conditions:
1. The minimum DC input voltage is 100 V or higher at 90 VAC
input. The value of the input capacitance should be large
enough to meet these criteria for AC input designs.
2. Secondary output of 5 V with a Schottky rectifier diode.
3. Assumed efficiency of 80%.
4. Continuous conduction mode operation (K
P
= 0.4).
5. Reflected Output Voltage (V
OR
) of 110 V.
6. The part is board mounted with SOURCE pins soldered to a
sufficient area of copper to keep the SOURCE pin tempera-
ture at or below 110 °C for P package and 100 °C for D
packaged devices.
7. Ambient temperature of 50 °C for open frame designs and
an internal enclosure temperature of 60 °C for adapter
designs.
Note: Higher output power are achievable if the efficiency is
higher than 80%, typically for high output voltage designs.
BYPASS Pin Capacitor
A 1
mF
BYPASS pin capacitor (C4) is recommended. The
capacitor voltage rating should be equal to or greater than
6.8 V. The capacitor’s dielectric material is not important.
The capacitor must be physically located close to the
LinkSwitch-CV BYPASS pin.
Circuit board layout
LinkSwitch-CV is a highly integrated power supply solution that
integrates on a single die, both the controller and the high-
voltage MOSFET. The presence of high switching currents and
5
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Rev. F 03/14
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