LNK603-606/613-616
LinkSwitch-II
Family
Energy-Efficient, Accurate CV/CC Switcher
for Adapters and Chargers
Product Highlights
Dramatically Simplifies CV/CC Converters
•
Eliminates optocoupler and all secondary CV/CC control circuitry
•
Eliminates all control loop compensation circuitry
Advanced Performance Features
•
•
•
•
•
Compensates for transformer inductance tolerances
Compensates for input line voltage variations
Compensates for cable voltage drop (LNK61X series)
Compensates for external component temperature variations
Very tight IC parameter tolerances using proprietary trimming
technology
•
Frequency jittering greatly reduces EMI filter cost
•
Even tighter output tolerances achievable with external resistor
selection/trimming
•
Programmable switching frequency up to 85 kHz to reduce trans-
former size
Wide Range
High-Voltage
DC Input
LinkSwitch-II
D
FB
BP/M
S
PI-4960-012315
(a) Typical Application Schematic
V
O
±5%
Advanced Protection/Safety Features
•
Auto-restart protection reduces power delivered by >95% for output
short-circuit and control loop faults (open and shorted components)
•
Hysteretic thermal shutdown – automatic recovery reduces power
supply returns from the field
•
Meets high-voltage creepage requirements between DRAIN and all
other pins both on the PCB and at the package
±10%
EcoSmart
™
– Energy Efficient
PI-4906-012315
•
Easily meets all global energy efficiency regulations
•
No-load consumption below 30 mW at 230 VAC with optional
(b) Output Characteristic
Figure 1.
I
O
external bias winding
•
ON/OFF control provides constant efficiency down to very light loads
– ideal for CEC and ENERGY STAR 2.0 regulations
•
No current sense resistors – maximizes efficiency
Typical Application/Performance – Not a Simplified Circuit (a) and
Output Characteristic Envelope (b). (see Application Section for
more information).
Green Package
Applications
Output Power Table
Product
3
LNK603/613PG/DG
LNK604/614PG/DG
LNK605/615PG/DG
LNK606/616PG/GG/DG
85-265 VAC
Adapter
1
2.5 W
3.5 W
4.5 W
5.5 W
Open Frame
2
3.3 W
4.1 W
5.1 W
6.1 W
•
Halogen free and RoHS compliant package
•
Chargers for cell/cordless phones, PDAs, MP3/portable audio
devices, adapters, LED drivers, etc.
Description
The LinkSwitch™-II dramatically simplifies low power CV/CC
charger
designs by eliminating an optocoupler and secondary control circuitry.
The device introduces a revolutionary control technique to provide very
tight output voltage and current regulation, compensating for transformer
and internal parameter tolerances along with input voltage variations.
The device incorporates a 700 V power MOSFET, a novel ON/OFF control
state machine, a high-voltage switched current source for self biasing,
frequency jittering, cycle-by-cycle current limit and hysteretic thermal
shutdown circuitry onto a monolithic IC.
Table 1. Output Power Table.
Notes:
1. Minimum continuous power in a typical non-ventilated enclosed adapter
measured at +50 °C ambient, device, T
J
<100 °C.
2. Maximum practical continuous power in an open frame design with adequate
heat sinking, measured at 50 °C ambient (see Key Applications Consider-
ations section for more information).
3. Packages: P: DIP-8C, G: SMD-8C, D: SO-8C.
DIP-8C (P Package)
Figure 2.
www.power.com
SMD-8C (G Package)
SO-8C (D Package).
Package Options.
August 2016
This Product is Covered by Patents and/or Pending Patent Applications.
LNK603-606/613-616
BYPASS
(BP/M)
FB
OUT
6V
5V
REGULATOR
6V
+
+
DRAIN
(D)
FEEDBACK
(FB)
V
TH
-
D
Q
STATE
MACHINE
I
LIM
Reset
V
ILIMIT
Drive
-
t
SAMPLE-OUT
CABLE DROP
COMPENSATION
6.5 V
INDUCTANCE
CORRECTION
V
ILIMIT
DC
MAX
FAULT
Auto-Restart
Open-Loop
THERMAL
SHUTDOWN
t
SAMPLE-OUT
t
SAMPLE-INPUT
OSCILLATOR
+
FB
t
SAMPLE-INPUT
DC
MAX
SAMPLE
DELAY
SOURCE
(S)
CONSTANT
CURRENT
I
LIM
SOURCE
(S)
V
ILIMIT
LEADING
EDGE
BLANKING
-
Current Limit
Comparator
PI-4908-012915
Figure 3.
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/MULTI-FUNCTIONAL PROGRAMMABLE (BP/M) Pin:
P Package (DIP-8C)
G Package (SMD-8C)
FB
BP/M
1
2
8
7
6
D
4
5
S
S
S
S
D Package (SO-8C)
1
2
8
7
6
D
4
5
This pin has multiple functions:
1.
It is the connection point for an external bypass capacitor for the
internally generated 6 V supply.
2.
It is a mode selection for the cable drop compensation for
LNK61X series.
FB
BP/M
S
S
S
S
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 both the output voltage in CV mode and output
current in CC mode based on the flyback voltage of the bias winding.
The internal inductance correction circuit uses the forward voltage on
the bias winding to sense the bulk capacitor voltage.
SOURCE (S) Pin:
This pin is internally connected to the output MOSFET source for
high-voltage power and control circuit common returns.
PI-3491-020615
Figure 4.
Pin Configuration.
2
Rev. J 08/16
www.power.com
LNK603-606/613-616
LinkSwitch-II Functional Description
The LinkSwitch-II 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. In addition, the switching frequency is modulated
to regulate the output current to provide a constant current
characteristic. The LinkSwitch-II controller consists of an oscillator,
feedback (sense and logic) circuit, 6 V regulator, over-temperature
protection, frequency jittering, current limit circuit, leading-edge
blanking, inductance correction circuitry, frequency control for
constant current regulation and ON/OFF state machine for CV control.
Inductance Correction Circuitry
If the primary magnetizing inductance is either too high or low the
converter will automatically compensate for this by adjusting the
oscillator frequency. Since this controller is designed to operate in
discontinuous-conduction mode the output power is directly
proportional to the set primary inductance and its tolerance can be
completely compensated with adjustments to the switching
frequency.
Constant Current (CC) Operation
As the output voltage and therefore the flyback voltage across the
bias winding increases, the FEEDBACK pin voltage increases. The
switching frequency is adjusted as the FEEDBACK pin voltage
increases to provide a constant output current regulation. The
constant current circuit and the inductance correction circuit are
designed to operate concurrently in the CC region.
Constant Voltage (CV) Operation
As the FEEDBACK pin approaches V
FBth
from the constant current
regulation mode, the power supply transitions into CV operation.
The switching frequency at this point is at its maximum value,
corresponding to the peak power point of the CC/CV characteristic.
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.
Output Cable Compensation
This compensation provides a constant output voltage at the end of
the cable over the entire load range in CV mode. As the converter
load increases from no-load to the peak power point (transition point
between CV and CC) the voltage drop introduced across the output
cable is compensated by increasing the FEEDBACK pin reference
voltage. The controller determines the output load and therefore the
correct degree of compensation based on the output of the state
machine. Cable drop compensation for a 24 AWG (0.3
W)
cable is
selected with C
BP
= 1
mF
and for a 26 AWG (0.49
W)
cable with
C
PB
= 10
mF.
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-II enters into an appropriate protection
mode as described below.
In the event the FEEDBACK pin voltage during the flyback period falls
below 0.7 V before the FEEDBACK pin sampling delay (~2.5
ms)
for a
duration in excess of ~450 ms (auto-restart on-time (t
AR-ON
) the
converter enters into auto-restart, wherein the power MOSFET is
disabled for 2 seconds (~18% 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
450 ms to approximately 6 clock cycles (90
ms),
whilst keeping the
disable period of 2 seconds.
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. The LinkSwitch-II
also contains a “di/dt” correction feature to minimize CC variation across
the input line range.
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-II to
operate continuously from the current drawn from the DRAIN pin.
A bypass capacitor value of either 1
mF
or 10
mF
is sufficient for both
high frequency decoupling and energy storage.
3
www.power.com
Rev. J 08/16
LNK603-606/613-616
Applications Example
C6
R7
1 nF
100 V 200
Ω
L1
1.5 mH
R2
470 kΩ
C3
820 pF
1 kV
5
T1
EE16
10
5 V, 555 mA
D7
SS14
C7
680
µF
10 V
D1
1N4007
RF1
8.2
Ω
2W
D2
1N4007
3
8
1
R8
200
Ω
DC
Output
R3
300
Ω
D5
1N4007
2
VR1
2MM5230B-7
4.7 V
AC
Input
C1
4.7
µF
400 V
C2
4.7
µF
400 V
4
NC
D3
1N4007
D4
1N4007
LinkSwitch-II
U1
LNK613DG
D
D6
LL4148
FB
BP
R5
13 kΩ
1%
S
C4
1
µF
25 V
R4
6.2 kΩ C5
10
µF
16 V
R6
8.87 kΩ
1%
PI-5111-012315
Figure 5.
Energy Efficient USB Charger Power Supply (74% Average Efficiency, <30 mW No-load Input Power).
Circuit Description
This circuit shown in Figure 5 is configured as a primary-side
regulated flyback power supply utilizing the LNK613DG. With an
average efficiency of 74% and <30 mW no-load input power this
design easily exceeds the most stringent current energy efficiency
requirements.
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,
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, even with the output connected to safety earth ground.
Fusible resistor RF1 provides protection against catastrophic failure.
This should be suitably rated (typically a wire wound type) to
withstand the instantaneous dissipation while the input capacitors
charge when first connected to the AC line.
LNK 613 Primary
The LNK613DG device (U1) incorporates the power switching device,
oscillator, CC/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 is completely self-powered from
the BYPASS pin and decoupling capacitor C4. For the LNK61X
devices, the bypass capacitor value also selects the amount of output
cable voltage drop compensation. A 1
mF
value selects the standard
compensation. A 10
mF
value selects the enhanced compensation.
Table 2 shows the amount of compensation for each device and
bypass capacitor value. The LNK60x devices do not provide cable
drop compensation.
The optional bias supply formed by D6 and C5 provides the operating
current for U1 via resistor R4. This reduces the no-load consumption
from ~200 mW to <30 mW and also increases light load efficiency.
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 an RCD-R clamp
consisting of D5, R2, R3, and C3.
Output Rectification
The secondary of the transformer is rectified by D7, a 1 A, 40 V
Schottky barrier type for higher efficiency, and filtered by C7. If
lower efficiency is acceptable then this can be replaced with a
1 A PN junction diode for lower cost. In this application C7 was sized
to meet the required output voltage ripple specification without
requiring a post LC filter. To meet battery self discharge requirement
the pre-load resistor has been replaced with a series resistor and
Zener network (R8 and VR1). However in designs where this is not a
requirement a standard 1 kW resistor can be used.
Output Regulation
The LNK613 regulates the output using ON/OFF control in the
constant voltage (CV) regulation region of the output character-istic and
frequency control for constant current (CC) regulation. The feedback
resistors (R5 and R6) were selected using standard 1% resistor
values to center both the nominal output voltage and constant
current regulation thresholds.
4
Rev. J 08/16
www.power.com
LNK603-606/613-616
Key Application Considerations
Output Power Table
The data sheet maximum output power table (Table 1) repre-sents
the maximum practical continuous output power level that can be
obtained under the following assumed conditions:
LinkSwitch-II Output Cable Voltage Drop
Compensation
Device
LNK613
LNK614
LNK615
LNK616
Table 2.
BYPASS Pin
Capacitor Value
1
mF
10
mF
1
mF
10
mF
1
mF
10
mF
1
mF
10
mF
Output Voltage
Change Factor
1.035
1.055
1.045
1.065
1.050
1.070
1.060
1.090
1.
The minimum DC input voltage is 90 V or higher at 85 VAC input.
2.
3.
4.
5.
6.
The value of the input capacitance should be large enough to
meet these criteria for AC input designs.
Secondary output of 5 V with a Schottky rectifier diode.
Assumed efficiency of 70%.
Discontinuous mode operation (K
P
>1.3).
The part is board mounted with SOURCE pins soldered to a
sufficient area of copper to keep the SOURCE pin temperature at
or below 90 °C.
Ambient temperature of 50 °C for open frame designs and an
internal enclosure temperature of 60 °C for adapter designs.
Cable Compensation Change Factor vs. Device and BYPASS Pin
Capacitor Value.
Note: Higher output power are achievable if an output CC tolerance
>±10% is acceptable, allowing the device to be operated at a higher
SOURCE pin temperature.
of the power supply. See Figure 6 for a recommended circuit board
layout for LinkSwitch-II.
When designing a printed circuit board for the LinkSwitch-II 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-II 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-II device. This minimizes noise coupling.
Thermal Considerations
The copper area connected to the SOURCE pins provides the
LinkSwitch-II heat sink. A good estimate is that the LinkSwitch-II will
dissipate 10% of the output power. Provide enough copper area to
keep the SOURCE pin temperature below 90 °C. Higher temperatures
are allowable only if an output current (CC) tolerance above ±10% is
acceptable. In this case a maximum SOURCE pin temperature below
110 °C is recommended 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
An trace is placed along the isolation barrier to form one electrode of
a spark gap. The other electrode on the secondary is formed by the
output return node. The spark gap directs ESD energy from the
secondary back 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.
Drain Clamp Optimization
LinkSwitch-II senses the feedback winding on the primary side to
regulate the output. The voltage that appears on the feed-back
Output Tolerance
LinkSwitch-II provides an overall output tolerance (including line,
component variation and temperature) of ±5% for the output voltage
in CV operation and ±10% for the output current during CC operation
over a junction temperature range of 0 °C to 100 °C for the P/G
package. For the D package (SO8) additional CC variance may occur
due to stress caused by the manufacturing flow (i.e. solder-wave
immersion or IR reflow). A sample power supply build is
recommended to verify production tolerances for each design.
BYPASS Pin Capacitor Selection
For LinkSwitch-II 60x Family of Devices (without output
cable voltage drop compensation)
A 1
mF
BYPASS pin capacitor is recommended. The capacitor voltage
rating should be greater than 7 V. The capacitor’s dielectric material
is not important but tolerance of capacitor should be ≤ ±50%. The
capacitor must be physically located close to the LinkSwitch-II
BYPASS pin.
For LinkSwitch-II 61x Family of Devices (with output cable
voltage drop compensation)
The amount of output cable compensation can be selected with the
value of the BYPASS pin capacitor. A value of 1
mF
selects the
standard cable compensation. A 10
mF
capacitor selects the enhanced
cable compensation. Table 2 shows the amount of compensation for
each LinkSwitch-II device and capacitor value. The capacitor can be
either ceramic or electrolytic but tolerance and temperature variation
should be ≤ ±50%.
The output voltage that is entered into PIXls design spreadsheet is
the voltage at the end of the output cable when the power supply is
delivering maximum power. The output voltage at the terminals of
the supply is the value measured at the end of the cable multiplied by
the output voltage change factor.
LinkSwitch-II Layout Considerations
Circuit Board Layout
LinkSwitch-II 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 voltages
together with analog signals makes it especially important to follow
good PCB design practice to ensure stable and trouble free operation
5
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Rev. J 08/16
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